Study of the Photoproduction of 8Li with the Reaction9Be(γ,p)8Li

Mémoire

Nikita Bernier

Maîtrise en PhysiqueMaître ès sciences (M.Sc.)

Québec, Canada

© Nikita Bernier, 2013

Résumé

Le laboratoire TRIUMF se spécialise dans la production de faisceaux d’ions rares radioactifs qui

sont fondamentaux en physique nucléaire et de la matière condensée, entre autres. TRIUMF

construit présentement un accélérateur linéaire d’électrons supraconducteur de 50 MeV, 10 mA

dans le cadre du projet ARIEL. Les électrons accélérés seront utilisés pour produire des fais-

ceaux radioactifs par photo-désintégration. Le faisceau d’électrons est « converti » en photons

par le rayonnement de freinage des électrons lorsqu’ils traversent un matériau de Z élevé placé

directement devant la cible de production. La cible utilisée initialement sera du 9Be afin de pro-

duire du 8Li. Le 9Be est intégré dans un composé de BeO fabriqué à TRIUMF et conçu d’après

les spécifications de l’IPN Orsay où les tests préliminaires prendront place pendant la construc-

tion d’ARIEL. La puissance déposée dans la cible et la production d’isotopes rares sont calculées

avec le code de simulations Monte Carlo FLUKA.

iii

Abstract

The TRIUMF laboratory in Vancouver B.C. is a world leader in the production of rare radioactive

ion beams. Such beams are fundamental in research for nuclear physics, nuclear astrophysics

and solid state science among others. TRIUMF is constructing a 50 MeV, 10 mA superconducting

electron linac as part of its ARIEL project. The accelerated electrons will be used to produce RIB

through photodisintegration. The electron beam is “converted” into photons by braking radiation of

the electrons passing through a high Z material placed immediately before the production target.

The initial target to be employed is 9Be, used to produce a 8Li beam. The 9Be is imbedded in

a BeO compound manufactured at TRIUMF and designed following specifications of IPN Orsay

where the preliminary tests will be conducted while ARIEL is being constructed. Both the power

deposition and rare isotope production rates were calculated using the Monte Carlo simulation

package FLUKA.

v

Table of Contents

Résumé iii

Abstract v

Table of Contents vii

List of Tables ix

List of Figures xi

List of Acronyms and Abbreviations xv

Acknowledgements xix

Introduction 11.1 Research Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 TRIUMF Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 ARIEL Facility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Review of Literature 52.1 Photoproduction of Radioactive Ions . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2 Target Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

FLUKA Simulations 153.1 FLUKA and FLAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.2 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Target Material 394.1 Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.2 Pressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Preliminary Tests 575.1 Results from 2010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Conclusion 59

vii

A FLUKA Input File 61

B Isotope Production Rates 71

References 79

viii

List of Tables

3.1 Summary of ALTO target assembly measurements as modelled in FLUKA . . . . . . . 193.2 CPU time used for different runs in FLUKA . . . . . . . . . . . . . . . . . . . . . . . . 244.1 Characteristics of the BeO disks punched from the first cast recipe . . . . . . . . . . . 414.2 Characteristics of the BeO pellets batch #1 (pressed from 30% w/w PVB and BeO

powder washed with acetone) before and after sintering . . . . . . . . . . . . . . . . . 444.3 Characteristics of the BeO pellets batch #2 (pressed from 30% w/w PVB and BeO

powder washed with acetone on a greased Teflon sheet) before and after sintering . . 474.4 Energy-dispersive X-ray spectroscopy (EDX) on BeO pellets batch #2 pressed from

30% w/w PVB and BeO powder washed with acetone on a greased Teflon sheet [Per-formed at the UBC X-ray Crystallography facility] . . . . . . . . . . . . . . . . . . . . . 50

ix

List of Figures

1.1 Beam lines and experimental facilities at TRIUMF, including ARIEL. [Drawing by TRIUMF]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 (a) Gamma-quanta spectrum produced by electrons with various energies (left-handscale) and Experimental points for the 238U photofission cross section (right-handscale), and (b) Fission yield per electron for 238U as a function of the electron energy. [2] 7

2.2 Transmitted intensity as a function of the distance x travelled in a material for alphas,electrons and gammas. [3] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 Setup representation and diagram of the (a) d(e,p)e’n and (b) d(γ,p)n reactions in thelaboratory frame showing various kinematical quantities associated with each particle[5]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.4 Cross section for the reaction 9Be(γ, p)8Li as a function of the incident photon energyby (a) [6] and by (b) [7]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.5 (a) Percent theoretical density of BeO after two hours at temperature in vacuum, and(b) Percent theoretical density of BeO after two hours at temperature in various dryatmospheres. [11] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.6 (a) Rate of sintering of BeO in hydrogen, and (b) Grain size vs. sintering time for BeO.[12] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.7 The grain growth of UOX berrylium oxide in vaccum. [9] . . . . . . . . . . . . . . . . . 143.1 FLUKA input file viewed with the FLAIR interface. . . . . . . . . . . . . . . . . . . . . 163.2 Components of ALTO target assembly. [Drawings by CERN and IPN Orsay] . . . . . . 183.3 Modelling of the BeO target geometry in FLUKA according to ALTO specifications. . . 193.4 Modelling of the target oven left endcap and Ta converter with different thicknesses in

FLUKA according to ALTO specifications. . . . . . . . . . . . . . . . . . . . . . . . . . 193.5 Implementation of importance biasing in FLUKA by increasing the importance of the

different target regions along the target length z by a factor of 2. . . . . . . . . . . . . 233.6 8Li production rate as a function of the converter thickness with a 50 MeV electron

beam at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3. . . . . . . . . 253.7 8Li production rate as a function of the electron beam energy at an intensity I = 10 µA

for BeO pellets of different densities with a 0.8X0 converter (with and without biasing). . 263.8 8Li production rate per pellet with electron beams of different energies at an intensity

I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter. . . . . . . . 263.9 Beam particle fluence on the XZ plane in [beam particle/cm2/s] with electron beams

of different energies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3

with a 0.8X0 converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293.10 Beam particle fluence as a function of the penetration length z in [beam particle/cm2/s]

with electron beams of different energies at an intensity I = 10 µA for BeO pellets ofdensity ρ = 3.01 g/cm3 with a 0.8X0 converter. . . . . . . . . . . . . . . . . . . . . . . 30

xi

3.11 Electron fluence on the XZ plane in [electron/cm2/s] with electron beams of differentenergies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a0.8X0 converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.12 Electron fluence as a function of the penetration length z in [electron/cm2/s] with elec-tron beams of different energies at an intensity I = 10 µA for BeO pellets of densityρ = 3.01 g/cm3 with a 0.8X0 converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.13 Photon fluence on the XZ plane in [photon/cm2/s] with electron beams of differentenergies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a0.8X0 converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.14 Photon fluence as a function of the penetration length z in [photon/cm2/s] with elec-tron beams of different energies at an intensity I = 10 µA for BeO pellets of densityρ = 3.01 g/cm3 with a 0.8X0 converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.15 Deposited power per pellet with electron beams of different energies at an intensityI = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter. . . . . . . . 35

3.16 Deposited power per region as a function of the electron beam energy at an intensityI = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter. . . . . . . . 35

3.17 Deposited power on the XZ plane in [W/cm3] with electron beams of different ener-gies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0

converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.18 Deposited power as a function of the penetration length z in [W/cm3] with electron

beams of different energies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3

with a 0.8X0 converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.1 BeO casts which were (a) uncovered and (b) covered during the drying process. . . . 404.2 (a) 14-mm diameter press die and (b) 1-ton manual press used to make BeO pellets. . 424.3 Chemical reactions showing as colour variations during the sintering in furnace of

Al2O3 pellets pressed from 30% w/w PVB and Al2O3 powder washed with acetone. . . 444.4 Sintering of BeO pellets batch #1 pressed from 30% w/w PVB and BeO powder wa-

shed with acetone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.5 SEM pictures on BeO pellets batch #1 pressed from 30% w/w PVB and BeO powder

washed with acetone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464.6 Reaction between the Ta target boat and the target material during the sintering of

BeO pellets batch #2 (pressed from 30% w/w PVB and BeO powder washed withacetone on a greased Teflon sheet). . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.7 EPICS screen captures of a reaction between the Ta target boat and the target ma-terial during the sintering of BeO pellets batch #2 (pressed from 30% w/w PVB andBeO powder washed with acetone on a greased Teflon sheet), with vacuum pressurein red, current in brown (left-hand scale) and voltage in green). . . . . . . . . . . . . . 49

4.8 SEM pictures on sintered BeO pellets batch #2 pressed from 30% w/w PVB and BeOpowder washed with acetone on a greased Teflon sheet. . . . . . . . . . . . . . . . . 50

4.9 Powder diffraction analysis on BeO pellets batch #2 pressed from 30% w/w PVB andBeO powder washed with acetone on a greased Teflon sheet. [Performed at the UBCX-ray Crystallography facility] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

4.10 Power failure during the sintering of BeO pellets batch #3 pressed from 30% w/w PVB,mineral oil and BeO powder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

4.11 Reaction between the Ta target boat and the target material during the sintering ofBeO pellets batch #4 pressed from 30% w/w PVB, mineral oil and BeO powder. . . . . 53

4.12 Sintering of BeO pellets batch #5 pressed from 30% w/w PVB, mineral oil and BeOpowder. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

xii

5.1 8Li production rates [y-axis in pps] as a function of the electron beam energy [x-axisin MeV] obtained at ALTO Orsay at an intensity I = 10 µA in December 2010 with aprevious BeO target and a 250 micron thick Ta converter. [22] . . . . . . . . . . . . . 58

xiii

List of Acronyms and Abbreviations

�TRIUMF : TRI-University Meson Facility,

Canada’s national laboratory

for particle and nuclear physics,

located in Vancouver, BC.�ISAC : Isotope Separator and ACcelerator,

installation dedicated to the on-line

production of rare isotopes.�ARIEL : Advanced Rare IsotopE Laboratory,

it is an installation that is

designed to produce radio nuclide

from electron and proton beams.�RIB : Radioactive Ion Beam.�IPN : Institut de Physique Nucléaire,

located at Orsay, France.�ALTO : Accélérateur Linéaire et Tandem

d’Orsay.�LINAC : LINear ACcelerator.�FLUKA : FLUktuierende KAskade (fluctuating cascade),

Fully integrated Monte Carlo simulation

package for the interaction and transport

of particles and nuclei in matter, covering

an extended range of applications, including

proton and electron accelerator shielding and

target design.�FLAIR : FLuka Advance InteRace,

All-in-one user friendly graphical interface.�ISOL : Isotope Seperation On Line.

xv

For my love,Madame Lapine.

xvii

Acknowledgements

Mes remerciements à

Pierre Bricault, pour son ouverture et ses précieuses explications.

René Roy, pour sa direction conviviale et ses compétents conseils.

Anne Trudel, pour sa grande expérience et son irremplaçable savoir.

Aurelia Laxdal, pour son aide, son support et son amitié dans toutes les facettes du projet.

Ma famille, pour s’être séparée de moi pour que je puisse accomplir ces recherches.

Acknowledgements to

Peter C. Bender, for his great patience and support with programming and computer mat-

ters.

John Wong, for patiently teaching chemistry and the administrative functioning of TRIUMF

to a physicist.

Rick Maharaj, for understanding John’s crazy ideas and making them reality, enabling us to

always go forward.

Evidently, the support of

xix

Introduction

1.1 Research Project

There are two main methods to produce intense radioactive ion beams : isotopic separation on-

line and the in-flight fragmentation. In the Isotope Separation On-Line (ISOL) method, light ions

impinge onto a thick target and produce a large variety of radioactive species. Producing beams

in this manner produces what is colloquially known as a “cocktail”, where not only the nuclei of

interest are produced but also many others from the different possible outcomes of the beam and

primary target combination. These cocktails are then sent through mass separators, where the

isotope of interest can be finely selected. Once an ion beam is produced, it is mass analyzed and

either sent directly to an experimental station or reaccelerated, depending on the type of expe-

riment to be carried out. Experiments with radioactive ion beams cover a wide range of fields from

nuclear astrophysics, to material science and a broad range of topics in each field. Radioactive

ion beams have been proven essential to these fields and in turn, much of the work happening at

laboratories like TRIUMF, Canada’s national laboratory for particle and nuclear physics, revolves

around them.

TRIUMF is currently upgrading its radioactive beam capabilities by constructing a superconduc-

ting linear accelerator capable of delivering a 10 mA electron beam at 50 MeV as part of its future

Advanced Rare IsotopE Laboratory (ARIEL) project. The ARIEL project is in the first phase, which

began in the fall of 2011. This phase includes the construction of both the superconducting linear

electron accelerator and the construction of the primary target hall. The second phase, starting

mid-2014, will see the installation of the primary target station for the production of the first radio-

active isotopes while the electron intensity and energy will be limited to 4 mA and 25 MeV.

This is enough energy to start a program producing 8Li, and possibly 6He, for material science

using a beryllium oxide (BeO) target. This target was chosen because of the short-lived nuclei

produced, which in turn allows last minute adjustments to be made with minimum concerns for

safety, considering that the funding for the hot cells and the shielding in ARIEL has not been recei-

ved. Since the ARIEL electron linac is not readily available, the preliminary tests were conducted

1

at ALTO accelerator in Orsay where they have a 10 µA, 50 MeV electron linac equipped with an

ISOL system.

Even during the first phase of ARIEL, the electron beam will have too much power to be applied

directly to the target. That is, 100 kW with 4 mA at 25 MeV. Applying such beam would simply

cause the target to melt, which does not bode well for the production of radioactive beams. Howe-

ver, by placing a high Z material such as Ta or W directly in front of the production target, called a

converter, the electrons effectively generate photons over a continuous energy spectrum from 0

to the maximal energy available. Presently the converter is planned to be composed of a Ta disc

cooled with de-ionized water.

The primary concern of this thesis is the characterization of the photoproduction of 8Li through

the reaction 9Be(γ,p)8Li along with the design of the target assembly needed to carry out the

reaction.

The objectives of this thesis are to cover :

� the modeling of the photodisintegration of 9Be using FLUKA simulations,

� the manufacturing of the BeO target needed to produce radioactive beams of 8Li, and

� the preparation for conducting tests with the constructed target at ALTO linear electron

accelerator at IPN Orsay.

The 8Li beam, which is in large demand in both condensed matter and material science, is produ-

ced through the photodisintegration of 9Be discussed in more detail below. Many of the produced8Li nuclei are stopped within the bulk of the target material. Thus, the target material operates at

high temperature to ease the diffusion process of the 8Li in the grain and speed up the effusion

process once the atoms have reached the surface of the grain. The neutral atoms then randomly

move until they reach the transfer tube and finally the ion source. In the following section, a back-

ground of RIB production, photodisintegration reactions, and also the ceramic processing are

discussed in the light of available literature.

To prepare for the future ARIEL experiment, Monte Carlo simulations have been performed using

FLUKA [13] to help model the target behaviour interacting with the beam. The FLUKA framework

represents a great advantage in providing all the necessary physical processes and constants in

a very reliable manner without having to start from scratch. These simulations allow us to study

the production rates as a function of the beam energy. From that, the optimum thickness and

composition of the target with different incident electron energies are computed. Also of interest

is the power deposition in the target. The third section of this thesis covers the initialization of the

simulations done using FLUKA and a summary of their results.

Finally in preparation for the electron beams at ARIEL, the BeO target is planned to undergo a

test run at Institut de Physique Nucléaire in Orsay, France. Unlike the beams that will be available

at the future ARIEL facility, the electron beams presently available at ALTO-IPN Orsay have a

maximum power of 500 W with 10 µA at 50 MeV. With this beam power an electron-to-photon

2

converter is not needed. The BeO production target to be used in this test has been manufactured

at TRIUMF as part of the work of this thesis, and designed from specifications to be used at ALTO-

IPN Orsay. Different ceramic techniques, such as casting and dry pressing, are used to produce

the high quality target. The fourth section of this thesis gives the steps and procedures for making

the target material while the fifth section presents the results of the previous tests at IPN Orsay.

1.2 TRIUMF Laboratory

TRIUMF is Canada’s national laboratory for particle and nuclear physics, located in Vancouver,

BC. The core of TRIUMF is its 500 MeV cyclotron, which accelerates H− ions up to 75% of the

speed of light. By placing a graphite foil in the path of the H− beam inside the cyclotron, the two

electrons are stipped away leaving an H+ nucleus, or simply a proton. Having an opposite charge

than the H−, the proton beam hence produced is ejected out of the cyclotron into the extraction

beam line which transports the proton beams to different experimental stations where scientists

study a broad range of fields such as material science, medical physics, isotope production and

many more.

As seen on Figure 1.1, one of those proton beams goes into the ISAC-I facility, which stands

for Isotope Separator and Accelerator, constructed in 1998. This installation is dedicated to the

on-line production, separation and acceleration of rare isotopes (ISOL). The proton beam coming

from the cyclotron hits one of two target stations, hence producing ions but also neutrons, gamma

rays, and other particles. The production targets are made of material such as nickel oxide (NiO),

silicon carbide (SiC), uranium carbide (UCx) and many others. Of course, only one target can be

used at a time since there is only one proton beam and therefore only one radioactive ion beam

(RIB) can be produced at a time.

From the products of the reaction, we extract ions with an ion source and then separate out the

isotope of interest using a mass separator. The produced RIB can then be directly delivered to

an experimental station in ISAC-I such as 8π and TITAN which use low energy beams. Beams

produced in ISAC-I can also be accelerated using a Radio Frequency Quadrupole (RFQ) and a

Drift Tube Linac (DTL) to be used with experiments like DRAGON and TUDA. Finally, some of

these beams can also be accelerated up to 12% of the speed of light using a 40 MV supercon-

ducting linear accelerator in ISAC-II experimental hall (built in 2003), which hosts experiments

HERACLES, TIGRESS, IRIS and soon, EMMA.

1.3 ARIEL Facility

TRIUMF began the construction of a new facility called the Advanced Rare IsotopE Laboratory

(ARIEL) in the fall of 2011. This new installation will house two additional target stations, one used

with an incident electron beam and one with an incident proton beam, effectively tripling TRIUMF’s

3

production of simultaneous radioactive beams. The electron beam includes the addition of a new

electron linear accelerator capable of accelerating the electrons up to 50 MeV with an intensity

of 10 mA. Further, as part of the ARIEL project, a fourth proton beam will be extracted from the

main cyclotron with intensity up to 200 µA as shown on Figure 1.1.

Unlike the target/ion source assembly in use with the current ISAC facility, the target/ion source

at ARIEL must incorporate an electron-photon converter to better dissipate the power from the

electron beam. Indeed, the high intensity of its electron beam requires the use of a converter and

an absorber, to prevent the electrons from reaching the target material in order to decrease the

density of power deposited in it by the electrons.

A goal of ARIEL is, among others, to have a second driver to be able to deliver more than one

RIB at a time. However during the first three years of ARIEL (starting in mid-2014), the shiel-

ding around the two target stations will be minimal and the remote handling of highly radioactive

targets, such as uranium targets, will not be possible. Therefore, we will be focusing on the pro-

duction of rare isotopes which have short half-lives, such as those produced with a BeO target :8Li and 6He.

Figure 1.1 – Beam lines and experimental facilities at TRIUMF, including ARIEL. [Drawing byTRIUMF]

4

Review of Literature

2.1 Photoproduction of Radioactive Ions

Photofission is an alternative production method for RIB production, as opposed to direct ion

reaction, that has been proposed by W.T. Diamond (Chalk River) in 1999 [1]. The idea was then

demonstrated by Y.T. Oganessian in 2002 using a uranium target [2]. There are very few facilities

currently using electron beams for the production of radionuclides, ALTO at IPN Orsay and Flerov

Institute in Dubna being the only ones. These systems use electron beams having intensity in the

order of 10 to 50 µA at 50 and 25 MeV, respectively. The ARIEL project aims to increase the inten-

sity of the electron beam up to 4 mA during phase II and 10 mA in its final phase. Reaching these

high intensities leads to high power densities in the targets. Therefore the challenge for ARIEL

converter-target assembly is finding a solution to remove the heat deposited in the assembly, or

this will limit the maximum current that can be used and hence the yields of ion beams that can

be produced.

Electrons can be aimed directly on the production target where they will produce braking radiation

(photons), scattered electrons, neutrons, and fission products. However, electrons reaching the

target with an energy below 6 MeV, which represents over one half of the beam particles, will

only heat the target without producing any nuclear reactions. Since the reactions of interest are

produced mainly by the radiation rather than the direct electron beam, it is more effective to stop

the electrons in a separate material and produce a continuous gamma spectrum. These photons

are then transmitted into the isotope production target where they will induce photonuclear reac-

tions [1]. The use of a converter such as tantalum becomes necessary when the incident beam

power exceeds 1 kW as the target cannot survive a continuous bombardment directly with such

energetic electrons.

a. Photon Production

By passing through matter, electrons interact through the Coulomb interaction and radiate energy.

Such radiation is called braking radiation (or bremsstrahlung in German). The total energy loss

can be divided into two components, one due to the Coulomb scattering and one due to the bra-

king radiation. Nevertheless, the radiative energy loss dominates the stopping power for electrons

5

and positrons at high energy and in heavy materials [3]. This can be expressed as :

(dEdx

)radiat ion

=EρX0, (2.1)

where X0 is the radiation length and ρ the density of the material.

From the previous equation, it is possible to calculate the average energy loss of an electron with

initial energy E0 after travelling a distance x in a material :

Eavg = E0e−ρxX0 . (2.2)

From this, it is clear that X0 is the thickness of the material over which the average energy is

reduced by a factor e. It is called the radiation length and is given by the approximate formula :

X0 '716.4 A

Z(Z + 1)ln(287/√

Z)g/cm3 ∝ 1

Z2 , (2.3)

where Z and A are the atomic number and mass of the material [4]. Thus the number of gammas

is proportional to :

Nγ ∝Z2

X0. (2.4)

The energy distribution of the photons generated for different electron energy is continuous and

depends strongly on the electron energy Ee as seen on the left-hand scale of Figure 2.1a. The

most energetic photons have Eγ ∼ Ee .

As the photons travel through matter, they get attenuated. The attenuation of the photons is

described by :

dII

= −µ · dx ∝ Z2, (2.5)

where

I = −I0e−µx (2.6)

and where µ = τ +σ +κ cm−1 is the total probability per unit length for the absorption of a photon,

referred to as the total linear attenuation coefficient [3].

Figure 2.2 illustrates the fractional loss of intensity for alphas, electrons, and photons. Comparing

directly the electrons to the photons, one can see that the electron intensity decreases drastically

6

(a) (b)

Figure 2.1 – (a) Gamma-quanta spectrum produced by electrons with various energies (left-handscale) and Experimental points for the 238U photofission cross section (right-hand scale), and (b)Fission yield per electron for 238U as a function of the electron energy. [2]

Figure 2.2 – Transmitted intensity as a function of the distance x travelled in a material for alphas,electrons and gammas. [3]

approaching the nominal electron range (denoted Re) due to electrons scattered out of the beam,

while the photon intensity decreases exponentially with no sudden decrease before the nominal

range. This shows that photons not only have a deeper penetrating depth, but also have a much

higher intensity at depths well within the material.

Considering our BeO target with a converter, the electrons are converted to gammas via

7

(a)

(b)

Figure 2.3 – Setup representation and diagram of the (a) d(e,p)e’n and (b) d(γ,p)n reactions in thelaboratory frame showing various kinematical quantities associated with each particle [5].

bremsstrahlung radiation which will then allow for the photodisintegration reaction of the beryl-

lium nuclei 9Be(γ,p)8Li to take place. Without the converter, direct bombardment still enables

production of 8Li through electrodisintegration reaction : 9Be(e,p)8Li. Both cases are illustrated in

Figure 2.3. The electromagnetic interaction is carried out by the bremsstrahlung photons and by

virtual photons as well through Coulomb interaction. Thus, cascades of electron-positron pairs,

bremsstrahlung and secondary electrons are produced along the path of the incident electron as

well as photonuclear reactions [1].

b. Photonuclear Production Rate

Photodisintegration is the physical process by which a high-energy photon is absorbed by a nu-

cleus and causes the nucleus to enter an excited state, which immediately decays by emitting a

subatomic particle, such as a proton, neutron, or alpha particle. In the present case, a 9Be nucleus

emits a proton upon absorbing a photon of sufficient energy and becomes 8Li. For heavier nucleus

such as uranium, the main channels are the production of neutron by (γ,xn) where x =1, 2, 3...

and photon-induced fission, the nuclear reaction that involves the splitting of the uranium nucleus

into two fragments after the absorption of a high energy photon.

The probability of photofission, known as the photofission cross section, is determined by the

region of giant dipole resonance (GDR) [2]. This region is associated with a strong resonance

due to a dipole vibration of the nucleus. When the energy of the projectile (i.e. the electron) is

very near the vibration energy of the nucleus, the probability that the nucleus absorbs the energy

rises. As a result, it is more probable that the projectile will react with the nucleus and the cross

8

(a) (b)

Figure 2.4 – Cross section for the reaction 9Be(γ, p)8Li as a function of the incident photon energyby (a) [6] and by (b) [7].

section rises sharply. 9Be is too light to have a region of giant resonance but we still observe

the augmentation in the cross section. Theoretical calculations to determine cross sections have

large uncertainties and therefore they are typically determined experimentally. An example of

an observed cross section for the reaction 9Be(γ,p)8Li of 1.8 mb at 22 MeV is shown in Figure

2.4a. Figure 2.4b shows an evaluated cross section of 0.65 mb at 22 MeV, which means that

the experimentally measured parameter was combined with the predictions of nuclear model

calculations. The best configuration for producing the highest yield cannot be obtained from the

cross section only, and so detailed Monte Carlo calculations are needed in order to get the highest

production yield possible.

Then the production rate in the BeO target is obtained by combining the electron-photon conver-

sion yield and the photodesintegration cross section. This task is accomplished by integrating

the cross section over the photon energy from the threshold energy for the particular reaction

up to the full electron energy [1]. As discussed previously, the number of gammas produced in

the region of GDR depends strongly on the energy of the electrons Ee . Thus one can obtain the

dependence of the cross section σ(Ee) and estimate the disintegration, or fission, probability as a

function of Ee . Fission yield increases with Ee until it reaches a saturation point which shows as

a plateau as seen on Figure 2.1b. For uranium, Ee increases up to 30 MeV and then reaches a

plateau around 50 MeV. ARIEL will use a 50 MeV electron beam, allowing for the saturation point

for the fission rate to be achieved.

Finally the observed yield of radioactive ions is given by :

9

Y = σI0Nε1ε2ε3, (2.7)

where σ is the energy-dependent cross section for the specific reaction, I0 is the primary beam

intensity and N is the target thickness (in nuclei/cm²). The product of these first three terms gives

us the maximum possible yield for a given primary beam and target. The three ε factors are

efficiencies related to inevitable losses as follows [8] :

� ε1 is the efficiency of product diffusion to the target surface,

� ε2 is the release and transfer to the ion source, and

� ε3 is the ionization efficiency of the ion source.

The last factor is relevant to the development of the ion source, which is not covered by this thesis.

Therefore the next section will cover the influence of the target material on the yield.

2.2 Target Material

a. Product Release

One of the most important parameters of the system is the release yield of the ions produced

from the target material. The separation of the ions from the bulk target material is achieved by

heating a material with a low vapour pressure to a sufficiently high temperature so that the more

volatile nuclei of interest, which are stopped in the target, are released by diffusion and desorption

processes. As a result, the strongly bound sites in the solid targets may cause large losses for

the release of this particular specie [8].

This release yield, and consequently the RIB production rate, is very much influenced by the

target microstructure. That is, its density and purity. The density is usually stated as the thickness

of the target in g/cm² and the purity, in percentage. For an optimal performance the highest density

along with highest purity is desired in order to increase the number of nuclear reactions. However,

the difficulty in releasing the ions from the target material increases as the density of the target

increases.

The porosity and the grain size of the material are two important factors that determine the optimal

density of a target. On one hand the material needs to be porous enough to favour diffusion of light

isotopes. On the other hand large closed porosities will trap the atoms and have them condense

there rather than in the ion source. Additionally the temperature inside large pores is cooler than

in the bulk of the material and this further favours the condensation of atoms in the target. In

order to stimulate diffusion of light isotopes and condensation in the ion source itself, we need

the temperature gradient to be as small as possible throughout the target. In addition, high power

density also tends to locally overheat the target material and to dissociate chemical compounds

which may give rise to an unwanted gas load of the ion source [8].

10

Overall, the target material needs to be developed and manufactured so it can operate at the high

temperatures required to release the ions from the target material in a timely fashion, while having

a sufficient porosity to permit the fission fragments to migrate to the surface of a thick target [1].

b. Ceramic Processing

Control of grain size as well as density is known to be important for the stability of the irradiated

material. For this reason, a good understanding of the mechanisms responsible for sintering and

grain growth is desirable [9]. Both of these factors are determined by the treatment of the actual

powder and the sintering process (rate and temperature).

Tape casting is the traditional method used at TRIUMF for target manufacturing starting with a

powder. This process first involves a high speed treatment of the powder in a ball mill which

will blend and grind down the grain size of the powder. This is a crucial parameter for the final

porosity of the sintered material so when it is fired, it will easily sinter and become a single large

solid body [10]. Then a solvent and a dispersant are added. The former mainly enables to make

a fluid system that can be easily shaped and to dissolve the other additives, whereas the latter

breaks down the lumps and clusters of the powder. Further milling is necessary for the dispersant

to accomplish this dispersion (or the deagglomeration) process.

A plasticizer, a binder and a surfactant are the last additives before casting. Plasticizer is used to

give a plastic flow to the slip to insure that the dried cast is not too brittle. The binder is the very

important chemical that holds all the powder particles together. This is why the deagglomeration

of the powder is important, to allow the binder to get in between the molecules. The dispersion

determines how much the binder will stick to itself or to the powder molecules. This dispersion

being qualitative, is a trial and error process to find the sequence of manipulations which gives

satisfactory results. Finally, the surfactant gets rid of all the air bubbles created by the milling

process in order to have a more homogeneous solution with no air trapped in the slip.

The slip gets poured on a non sticky surface and solidification happens through evaporation of

the solvent and water contained in the additives. The dried cast is called a green body. For tape

casting, there is no compaction involved, the only force present being the internal tension from

the binder [10]. The next step is the firing which enables the burnout of the organic additives and

the sintering, which will be discussed in the next section.

Dry pressing is another method that can be used to form pellets, or compacts. Just as tape

casting, the powder undergoes a high speed treatment along with a dry binder to decrease the

mesh size of the power and improve its homogeneity. Then the mixture is pressed, with or without

a lubricant, using a steel die. The compressive force is applied with the press and the plastic flow

of the binder enables solidification [10]. This pressure breaks down the binder molecular chains

once again so that they can better surround the powder molecules.

11

c. Sintering

The first step of the sintering process is the degassing, where the burnout of the binder and the

organic molecules is enabled by firing the green body. As the additives and the trapped gases

are removed, a certain shrinkage occurs. This is also called densification and leads to the actual

sintering where the grains melt into each other. It happens at higher temperature and hopefully

results in a rugged ceramic pellet.

Density, porosity and texture of the final pellets are determined by the sintering temperature,

the sintering time (or rate) and the sintering environment. First, the temperature at which the

sintering takes place has a direct influence on the sintering rate. This phenomenon is observed

on Figure 2.5a. As the sintering temperature gets higher, the sintering rate increases and the final

relative density is higher. Moreover, a plateau is seen above which the sintering rate stabilizes.

This indicates that the theoretical density of BeO cannot be obtained by an increase of firing

temperature alone.

The sintering environment has been found to affect the densification process. For example, the

presence of water vapour in the sintering atmosphere retards the densification of BeO compacts

as discussed by E. A. Aitken [11] and seen in Figure 2.5b. This highlights the importance of

degassing before the sintering can take place, or the presence of volatile molecules trapped in the

pores may stop shrinkage and grain growth. Hence the final density could be less than expected.

Figure 2.6a highlights the relation between the density and the sintering rate. The final density

increases with the sintering time until it reaches a plateau similar to the one seen for the tempe-

rature. Furthermore, the grain size is directly affected by the sintering time as it can be seen on

Figure 2.6b. For sintering times shorter than 5 hours, the grain growth curve is directly propor-

tional to the time. But firing for a longer time results in more moderate increase in both density

and grain growth [12]. This suggests that the secondary grain growth has a great influence on

the densification rate, that is the rate at which porosity decreases. Figure 2.7 exhibits the same

relation between grain growth to sintering time, but also to temperature. From those results, one

sees that density and grain growth should be optimized in terms of sintering temperature and

time. By measuring the density and the average grain size using a scanning electron microscope

(SEM), we can achieve an optimal target material processing.

The sintering behaviour of green bodies is complex and varies widely. When performing a high

temperature vacuum treatment, the atmosphere and heating parameters must be carefully monitored.

Specifically, the power applied to the sintering container determines the temperature and indicates

a lot about what is happening inside the chamber. For example, a rise in resistance indicates that

a reaction is happening. That is, the pellets are reacting with the sintering container. Because of

this, control of the furnace characteristics is crucial.

12

(a) (b)

Figure 2.5 – (a) Percent theoretical density of BeO after two hours at temperature in vacuum, and(b) Percent theoretical density of BeO after two hours at temperature in various dry atmospheres.[11]

(a) (b)

Figure 2.6 – (a) Rate of sintering of BeO in hydrogen, and (b) Grain size vs. sintering time for BeO.[12]

13

Figure 2.7 – The grain growth of UOX berrylium oxide in vaccum. [9]

14

FLUKA Simulations

3.1 FLUKA and FLAIR

FLUKA is a fully integrated Monte Carlo simulation package for the interaction and transport

of particles and nuclei in matter, covering an extended range of applications : from proton and

electron accelerator shielding to target design, calorimetry, activation, dosimetry, detector design,

accelerator driven systems, cosmic rays, neutrino physics, radiotherapy, etc., FLUKA can simu-

late with high accuracy the interaction and propagation in matter of about 60 different particles,

including photons and electrons from 1 keV to thousands of TeV, neutrinos, muons of any energy,

hadrons of energies up to 20 TeV and all the corresponding antiparticles, neutrons down to ther-

mal energies and heavy ions [13].

The process of a particle moving through and interacting with a medium is governed by the laws

of probability. Because every step of a particle through a medium can be directly related to a

probability of interacting with that medium, a random walk or Monte Carlo technique lends itself

naturally to perform these simulations. A Monte Carlo simulation consists in following each par-

ticle on its path through matter, from its birth to its disappearance (by absorption or escape). At

each interaction of the particle with matter, the occurrence and the outcome are decided by a

random selection from the appropriate probability distribution functions of the different allowed

interactions. These distributions, also known as cross sections, are defined as the interaction pro-

babilities per unit distance. The accuracy and reliability of a Monte Carlo simulation depend on the

models or quality of data from which the probability distribution functions are derived. Statistical

accuracy of results depends on the number of “histories", and the statistical convergence can be

accelerated by “biasing" techniques [17].

A FLUKA simulation is controlled through a list of command lines called cards, a throw back to the

actual punch cards used in the early days of computing. The user determines which parameters to

include in the simulation by choosing which cards, from hundreds of available options, are given

to FLUKA during initialization. Each card is composed of 8 parameters called WHATs. Those

cards are read by FLUKA as lines of specific numbers which can always be seen using FLAIR, a

graphical user interface (GUI) for FLUKA. An example of a FLAIR window is shown in Figure 3.1.

FLAIR, the FLUKA Advance Interface, is an all-in-one user friendly graphical user interface to

15

Figure 3.1 – FLUKA input file viewed with the FLAIR interface.

facilitate the editing of FLUKA input files, execution of the code and visualization of the output

files. The philosophy behind the interface is to work on an intermediate level, not so high that

the inner functionality of FLUKA are hidden from the user, and not too low that the user is in

constant need of the FLUKA manual to verify the options for each card [13]. FLAIR provides mini-

dialogues for each card, allowing for easy and nearly error free editing. FLAIR also allows for

multiple setups/runs to be performed with only a single input file using preprocessor definitions.

Important features of FLAIR are shown Figure 3.1 such as the interactive geometry editor and

debugger, the manual, the database and the different plots of the results. For convenience, the

input cards are arranged by different categories. Compiling of the FLUKA executable, running and

monitoring can all also be controlled within the FLAIR interface.

3.2 Implementation

The great advantage of using the FLUKA code is that within its framework, FLUKA contains all

the necessary physical processes needed to perform a reliable simulation, and no code from

the user is required. FLUKA can also track the radiation produced during a simulation making it

very useful to estimate the shielding needed by an experimental area to be safe. With FLUKA,

the radionuclide production rate is relatively easy to be extracted based on the characteristics of

16

electron beam energy, beam size, thickness and type of the converter.

Previous work has checked the validity of the FLUKA code using another simulation code, GEANT4

[15]. Unlike FLUKA where the physics processes are all included, the GEANT4 code necessitates

the writing of a subroutine describing all the physical processes involved during the interaction.

In addition, GEANT4 does not automatically determine the production rate of specific isotopes di-

rectly and therefore, an integral between the resonance cross section and the number of photons

produced by bremsstrahlung must be performed to determine the number of induced fission. The

agreement between the two codes was quite good and provided the confidence needed to use

FLUKA for further simulations.

FLUKA has proven itself as the most appropriate code to simulate precisely the reactions oc-

curring within the target. The photon and the electron transport, which will be very important in

ARIEL, are provided directly by FLUKA. In addition, FLUKA takes into account the cross section

variation with respect to the electron energy and the continuous loss of electron energy. Because

of this, the bremsstrahlung radiation used in ARIEL to convert electrons into photons will be well

simulated.

The objectives of simulating with FLUKA are :

� to study the impact of the converter on the production rates,

• optimum thickness,

• thickness of the material to stop the electrons after passing through the converter,

� to optimize the geometry of the target, and

� to determine the power dissipated in the target.

First, the best geometry of the converter/target combination was determined for the size of the

electron beam. In other words, the thickness of the tantalum converter was optimized to get the

highest 8Li production rate for a 50 MeV electron beam. This converter thickness was used to

study the 8Li production rate for beams of different energies between 20 and 50 MeV. This two-

step optimization provided the optimal power density in the converter and in the target and will

prove to be extremely useful for extrapolations to ARIEL’s operating power of 100 kW.

The following covers in great details the creation of the input file for the FLUKA simulation. The

intent is to be a step by step guide and a collection of tips useful to the FLUKA beginner to

intermediate user needing to deal with an electron beam for the first time. This is the kind of help

I wished I would have had while I was starting with FLUKA. What I did not find out on my own

came from the FLUKA manual [13]. The complete FLUKA input file can be found in Appendix A.

17

a. Geometry Setup

The different parts of the target assembly that is used with ATLO are shown in Figures 3.2, 3.3

and 3.4, and the measurements are summarised in Table 3.1. They highlight how these parts

are modelled in FLUKA. Different thicknesses of the tantalum converter are used to optimize the

target assembly, as shown in Figure 3.4b. Using preprocessor cards #define, #if and #endif, a

single input file was created containing the four different converter thicknesses. The thickness of

the converter was expressed in factors of the radiation length of tantalum, X0 = 0.409 cm.

The target geometry shown in Figures 3.3 and 3.4 was made only from infinite cylinders and

infinite planes, referred to as bodies. Only infinite bodies are used due to problems created from

overlapping non-infinite geometries during run time. These bodies were joined into zones and

regions with Boolean expressions. It is important to avoid using parentheses as they also can

create run time errors. Since the material (with ASSIGNMA) and biasing (with BIASING) are

assigned by regions, four extra XYP planes were needed to cut the target in five sections as

shown in Figure 3.5.

(a) ALTO tantalum target oven and converter (b) ALTO Right and left tantalum legs

(c) ALTO graphite target container

Figure 3.2 – Components of ALTO target assembly. [Drawings by CERN and IPN Orsay]

18

Table 3.1 – Summary of ALTO target assembly measurements as modelled in FLUKA

Component Radius [cm] Thickness [cm] Length [cm] Tolerance [mm]

Ta target oven 1.05 0.05 20.2 ISO 2768-mKTa converter 1.05 - Varies ISO 2768-mK

Graphite container 0.95 0.20 19.4 ±0.2Graphite endcaps 1.5 and 1.9 - 0.5 +0.1, 0 and 0, -0.2BeO target pellets 0.7 - 0.55 -

(a) XY plane (b) XZ plane

Figure 3.3 – Modelling of the BeO target geometry in FLUKA according to ALTO specifications.

(a) XY Plane (b) XZ Plane

Figure 3.4 – Modelling of the target oven left endcap and Ta converter with different thicknessesin FLUKA according to ALTO specifications.

19

The LOW-MAT card is needed for the graphite material in order to set the correspondence bet-

ween the material and the low-energy neutron cross sections library. This library is activated

through the PRECISIOn defaults (or the LOW-NEUT card).

b. Other Cards

Defaults :

The DEFAULTS card is required when the primary beam is e-/e+ or photons. By setting it to PRE-

CISIOn, the defaults used enable precision simulations. This includes detailed transport of elec-

trons, positrons and photons with fully analogue absorption for low-energy neutrons and heavy

fragment transport. Some default thresholds are overwritten by EMFCUT and EMF-BIAS as des-

cribed further.

The primary beam parameters used are listed below :

Average beam kinetic energy E : 20, 30, 40, 50 MeV electron beam

Momentum spread type ∆p : Flat

Momentum spread ∆p : 0.01 GeV/c

∆p/p = 0.20

Divergence type ∆φ : Flat

Divergence ∆φ : 0.01 mrad

Beam shape in X axis : Annular

Maximum radius of annular beam spot : 0.5 cm.

Different BEAM cards are necessary to define the four different energies. As for the converter

thickness, the energy of the beam was also selected through the preprocessor cards #define, #if

and #endif. It is important that the beam does not start directly at a boundary. For example, the

beam should start before the target and not on the target.

Physics Cards :

Photonuclear interactions are activated at all energies and in all materials (@LastMat) through

the card PHOTONUC, which enables hadron photoproduction. This card is used along with LAM-

BIAS to artificially increase the probability of gamma interactions in order to enable more efficient

simulations. The strength of electromagnetic interactions at short distances is smaller than nu-

clear interactions by a factor 1/137 [16]. By setting the hadronic interaction length for nuclear

inelastic interactions of primary photons to 1/50 (reducing the factor by 50) in all materials, it

increases the probability of interaction by a factor 50.

Two more PHYSICS cards are needed as well for activation studies. The COALESCEnce card

governs the emission of fast complex particles and EVAPORATion card dictates the physics of

20

heavy fragment evaporation/fragmentation. These last cards are expensive in CPU time but es-

sential in order to achieve realistic and accurate results for residual nuclei production.

Transport :

EMFCUT cards are used to set production and transport thresholds. Setting the thresholds in

terms of kinetic energy helps to avoid any mistakes. For example, threshold values would be

meaningless if set to energies lower than the rest mass. The default value (1 MeV) applies in

all materials where the threshold is not specifically set. However, it is recommended not to rely

on the default value and to uniquely set a proper value for each material instead. Obviously,

setting thresholds to lower numbers increases the processing time as more interactions have to

be considered. With Type=PROD-CUT, production thresholds are set to 50 keV for e-/e+ and to

10 keV for photons in all materials.

If Type is left blank, EMFCUT will set the transport thresholds. The energy threshold for e-/e+ is

applied individually since the particles are generated in other processes than pair production. For

e-/e+ and photons, it is recommended to have the transport thresholds equal to the production

thresholds. This sets the transport thresholds to 50 keV for e-/e+ and 10 keV for photons in all

regions. WHAT(3) is set to 0 because it is preferable to activate the leading particle biasing (LPB)

through EMF-BIAS, as discussed later.

Activation Cards :

Decay of produced radioactive nuclides is requested with the card RADDECAY. The irradiation

profile is defined with IRRPROFI. Here, the target is irradiated for 10 days with an intensity of

10 µA [6.24146 x 1013 electron/s]. With DCYTIMES, the cooling time after which we wish to score

a particular quantity is set. By setting a negative cooling time, quantities are scored while the

irradiation is still ongoing.

Scoring with USRBIN Cards :

� Particle Fluence [particle/cm²/s]

Scoring the beam particle fluence with BEAMPART allows one to visually verify that the beam is

actually hitting the target where it should. This type of card is used to score the fluence of electrons

(all or beam particle only) and photons. To convert units of particle/cm²/primary to particle/cm²/s,

we use :

21

PF/cm2/s = I · PFFLUKA

= 10 µA · PF/cm2/pr imary

=10× 10−6 C/s

1.602× 10−19 C/pr imary· PF/cm2/pr imary

= 6.242× 1013 pr imary/s · PFFLUKA

(3.1)

� Deposited Power [W/cm³]

DCYSCORE associates a cooling time, defined with DCYTIMES, to the different scoring detec-

tors, while AUXSCORE associates a dose conversion coefficient. These cards can be set to

score the energy deposition after 10 days of irradiation and no cooling time. To convert units of

GeV/cm³/primary to GeV/cm³/s, we use :

DPW/cm3 = I · EDFLUKA

= 10 µA · EDGeV

cm3 · pr imary

=10× 10−6 C/s

1.602× 10−19 C/pr imary· 1.602× 10−19 J/eV · ED

GeVcm3 · pr imary

= 104 W · pr imary/eV · EDFLUKA

(3.2)

Scoring with SCORE card :

SCORE reports the energy deposited (total or electromagnetic only) in GeV/cm³/primary by region

in a table which is found under “Events by region” in the output file. Since FLUKA does not

compute volume, it sets the volume to 1 cm³ and gives the deposited energy in GeV/primary.

Scoring Residual Nuclei :

The total production rates of the different isotopes are obtained by a single RESNUCLEi card

applied to all regions. The production rate can also be calculated per region. The rates are given

in nuclei/primary. The activity of the residual nuclei after some cooling time is obtained by a

RESNUCLEi card associated with a DCYSCORE card and is given in Bq/cm³. By setting the

volume to 1 cm³, the activity is simply given in Bq. To convert units of nuclei/primary to particle/s,

we use the normalization factor :

22

Rpps = I · RFLUKA

= 10 µA · R nucleipr imary

=10× 10−6 C/s

1.602× 10−19 C/pr imary· R nuclei

pr imary

= 6.242× 1013 pr imary/s · RFLUKA

(3.3)

c. Biasing

The EMF-BIAS card sets e-/e+ and photon special biasing parameters. Here, leading particle

biasing (LPBEMF) is activated for all regions, all energies and all physical effects, that is, brem-

sstrahlung, pair production, positron annihilation at rest, Compton scattering, Bhabha and Moller

scattering, photoelectric effect and positron annihilation in flight. WHAT(1) is set to 1022 and sums

up all the physical effects for which the leading particle biasing is activated while WHAT(2) and

WHAT(3) are left blank. Biasing is turned on and off through preprocessor cards #define, #if and

#endif.

The importance biasing by region is considered the “safest” biasing technique as it is the simplest

and easiest to use. It biases the multiplicity of secondary particles as a particle crosses a region

boundary. Figure 3.5 shows the different regions assigned. With the BIASING cards, the impor-

Figure 3.5 – Implementation of importance biasing in FLUKA by increasing the importance of thedifferent target regions along the target length z by a factor of 2.

23

tance of regions is increased by a factor of 2 through the target sections. By doing this, when

a particle goes to a region of higher importance, it undergoes surface splitting : the particle is

replaced by 2 similar particles and their statistical weight is divided by 2. When a particle goes to

a region of lower importance, it undergoes a Russian roulette process where its multiplicity might

be decreased as its statistical weight is doubled.

3.3 Results

The Run page in FLAIR allows overriding of the number of primaries set by the START card and

of the random number seed set by the RANDOMIZ card. This is also where the different prepro-

cessor selections are activated, such as the energy of the beam, the thickness of the converter

and the biasing.

Each simulation, or run, is composed of 10 cycles. For each cycle, 10,000,000 primary histories,

or number of events, are simulated for a total of 100× 106 primary electrons. A different random

number seed is selected for each run.

After a run, it is always important to look at the output file of the run to check for any error

and the CPU time used. Table 3.2 summarizes the CPU time used for different runs with and

without biasing. One can see that a considerable amount of computing time can be saved by

using biasing. However, it is important to verify that the biasing parameters used do not affect the

physics results obtained while the computing time is decreased. Again from Table 3.2, one can

see that more CPU time is needed to simulate primary particles as the energy is increased. This

increase in computation time is explained by the fact that more energetic particles undergo more

Table 3.2 – CPU time used for different runs in FLUKA

20MeV 30MeV 40MeV 50MeVNo With No With No With No With

biasing biasing biasing biasing biasing biasing biasing biasingTotal CPU time

used to follow allprimary particles

(CPU hours)

4.3 4.4 17.7 6.1 20.2 7.7 22.8 9.1

Average CPU timeused to follow aprimary particle

(CPU secs)

1.6× 10−3 1.6× 10−3 6.4× 10−3 2.2× 10−3 7.3× 10−3 2.8× 10−3 8.2× 10−3 3.3× 10−3

Maxium CPU timeused to follow aprimary particle

(CPU secs)

1.4× 10−1 1.6× 10−1 5.6× 10−2 1.6× 10−1 2.8× 10−2 2.1× 10−1 5.7× 10−2 1.7× 10−1

24

reactions requiring more calculations to be performed.

a. 8Li Production Rates

The data presented in Figure 3.6 was simulated using a 50 MeV beam on different converter thick-

nesses. Using these results, a 0.8X0 = 0.328 cm thick converter was determined best suited and

was used for the following simulations. It is important to note that electronuclear reactions are un-

derestimated in FLUKA. This could cause the production rates using thin converters to be higher

than calculated, considering that the electrons may reach the BeO pellets, which can produce 8Li

themselves through electrodesintegration of the Be. The contribution from electrodesintegration

cannot be estimated accurately until this issue gets implemented in FLUKA.

Simulated production rates of 8Li ions for different beam energies are presented here in Figure 3.7.

At 50 MeV, 8.24× 10−6 ions per primary electron are produced, which yields 5.14 x 108 pps at an

intensity of 10 µA. Moreover, one can see that the results with biasing are in good agreement with

the results obtained without biasing. This agreement indicates that the chosen biasing applied to

the simulation does not significantly affect the results obtained. By using biasing, the simulations

converge to the same value as the unbiased simulation and run considerably faster.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

Converter Thickness [*X0 cm]

3.5x108

4.0x108

4.5x108

5.0x108

5.5x108

6.0x108

8L

i P

rod

uc

tio

n R

ate

[p

ps

]

R2 = 0.877

Figure 3.6 – 8Li production rate as a function of the converter thickness with a 50 MeV electronbeam at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3.

25

10 20 30 40 50 60Beam Energy [MeV]

1×107

1×108

1×109

8L

i P

rod

uc

tio

n R

ate

[p

ps

]

3.01 g/cm3, No Biaising

3.01 g/cm3, With Biaising

1.90 g/cm3, With Biaising

Figure 3.7 – 8Li production rate as a function of the electron beam energy at an intensity I = 10 µAfor BeO pellets of different densities with a 0.8X0 converter (with and without biasing).

0 10 20 30

Pellet Number #

1x104

1x105

1x106

1x107

1x108

8L

i P

rod

uc

tio

n R

ate

[p

ps

]

20 MeV

30 MeV

40 MeV

50 MeV

Figure 3.8 – 8Li production rate per pellet with electron beams of different energies at an intensityI = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

26

The first two curves of Figure 3.7 were obtained by simulating pellets having the theoretical den-

sity of BeO, ρ = 3.01 g/cm3. A second simulation was run with BeO pellets of density ρ = 1.90 g/cm3,

which was the density of the first sintered pellets as discussed in Section 4.2. These results show

a decrease in the 8Li production rates by almost a factor of two. This difference is significant, but

not tragic since a less dense material will have a better release of the atoms than the denser

material. Since the density of the final pellets has not been determined yet, the results presented

here were obtained for a density of ρ = 3.01 g/cm3.

Figure 3.8 shows the 8Li production rate per pellet for different beam energies, all at an intensity

of 10 µA. The pellets simulated are 5.5 mm thick, for a total length of 18.7 cm. When adding

the production of each pellet, we get a total 8Li production rate of 5.054 × 108 pps for a incident

50 MeV electron beam, which is in good agreement with the 5.1370 × 108 pps seen in Figure 3.7.

The values differ by only 2% while the maximum error of the individual values is 3%. For a 20 MeV

electron beam, the total 8Li production rate obtained is 8.5763 × 106 pps, which differs from the

8.7661 × 106 pps value of Figure 3.7 by 2%. This difference is still under the average error of

12% for the individual values, with the maximum error being 18%. Here again the error at 20 MeV

is much more significant than at 50 MeV.

These results enable the optimal length, or the total number of pellets used, of the target to be

determined. If there is a region of the target volume which is very cold, the atoms would stick

there. That is, if the length z of the target is too long, the temperature at the end of the target will

be much cooler than at the beginning causing atoms to condense in the cold part of the target.

In order to favour the condensation of ions in the ion source rather than in the target itself, we

need the temperature gradient to be as small as possible throughout the target. To achieve this, a

study of the power deposited in the target as a function of z, the penetration length, needs to be

performed before determining the number of pellets.

The complete list of isotope production rates during the simulations can be found in Appendix B.

Also calculated is the residual activation five days after end of beam delivery.

b. Electron Intensity

Figures 3.9 and 3.10 show the fluence, or track length density, of the primary electrons. By com-

paring the maximum penetration depth of the beam electrons with and without biasing, one sees

that the values are very similar except for the tail where the statistics are not as good because

of the small number of simulated electrons reaching that thickness. Therefore this means that

the biasing does not affect the simulations results obtained for the penetration of the electrons

in the target. For a 50 MeV electron beam, we can safely assume that all primary electrons will

be stopped before reaching 10 cm in BeO. Figure 3.10 shows the loss in intensity of the beam

throughout the target and reminds one of Figure 2.2 which showed the transmitted intensity of

electrons decreases rapidly as a function the distance travelled.

27

Figures 3.11 and 3.12 show the fluence of all electrons, including the primary electrons. The

former gives a visual idea of the electrons distribution which is created by cascades of electron-

positron pairs, whereas the latter shows the exponential decay of the distribution. Also on these

figures, a second peak of electrons is observed right after z = 20 cm, where the tantalum endcap

releases more electrons. Finally, it can be noticed that the distribution increases with the beam

energy as one would expect.

c. Photon Attenuation

The fluence of the photons is presented in Figures 3.13 and 3.14. For a 50 MeV electron beam,

photon fluence is still of the order of 1012 at the very end of the target. This number explains the

photoproduction rates of 8Li seen in Figure 3.8 in the last pellets. Again, one can notice that the

distribution increases with the beam energy and that is much faster than the electron distribution

seen in Figure 3.11. In addition, Figure 3.13 clearly shows that the photons are produced within a

cone of large opening. Orsay target oven was not optimized for the production of photons. When

designing the target station for ARIEL, it will be possible of enlarging the radius of the target so

more photons get to react with it.

d. Deposited Power

Figure 3.15 shows that the energy deposited in the target increases rapidly with the energy of

the primary beam, as it is expected. The gradient between the first and the last pellets of the

target, however, is bigger by two orders of magnitude. This translates to an important temperature

gradient that favours the condensation of atoms at the end of the target. In such a situation, it may

be advantageous to use a shorter target. In that case, Figure 3.8 would indicate the total amount

of 8Li produced as a function of the number of pellets constituting the target.

Figure 3.16 shows the deposited power in the Ta converter, the BeO target (containing 34 pellets)

and the total volume as a function of the beam energy. Note that the values labelled as total

volume were integrated over the whole volume. The maximum incident power available at ALTO

IPN Orsay is 500 W with 10 µA at 50 MeV which corresponds to the value found for the total

volume at 50 MeV. From this figure, one can also notice that the deposited power in the converter

is relatively independent of the incident beam energy, near 103.93 W. With the beam power of

ARIEL during phase II, 41.16 kW are expected to be deposited in the Ta converter. Finally, if there

was no cooling system for the converter with a 500 kW electron beam, the power deposited would

be 103.93 kW.

For a more general picture, Figure 3.17 and 3.18 are presented here. The figures show the density

of deposited power in the target by all particles. First, it should be noted that the power density

results with and without biasing are in very good agreement. Again, the temperature gradient

between the beginning and the end of the target, all regions together, is bigger than an order of

magnitude, which does not represent an optimal situation.

28

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

(a) 20 MeV, No biasing

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

(b) 20 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

(c) 30 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

(d) 40 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

(e) 50 MeV

Figure 3.9 – Beam particle fluence on the XZ plane in [beam particle/cm2/s] with electron beamsof different energies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a0.8X0 converter.

29

1000

10000

100000

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[be

am

pa

rtic

le/c

m2/s

]

Z [cm]

(a) 20 MeV, No biasing

10000

100000

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[beam

part

icle

/cm

2/s

]

Z [cm]

(b) 20 MeV

1000

10000

100000

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[beam

part

icle

/cm

2/s

]

Z [cm]

(c) 30 MeV

1000

10000

100000

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[beam

part

icle

/cm

2/s

]

Z [cm]

(d) 40 MeV

10000

100000

1e+06

1e+07

1e+08

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[beam

part

icle

/cm

2/s

]

Z [cm]

(e) 50 MeV

Figure 3.10 – Beam particle fluence as a function of the penetration length z in [beamparticle/cm2/s] with electron beams of different energies at an intensity I = 10 µA for BeO pel-lets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

30

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

1e+14

(a) 20 MeV, No biasing

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

1e+14

(b) 20 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

1e+14

(c) 30 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

1e+14

(d) 40 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

1e+14

(e) 50 MeV

Figure 3.11 – Electron fluence on the XZ plane in [electron/cm2/s] with electron beams of differentenergies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

31

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[ele

ctr

on

/cm

2/s

]

Z [cm]

(a) 20 MeV, No biasing

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[ele

ctr

on/c

m2/s

]

Z [cm]

(b) 20 MeV

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[ele

ctr

on/c

m2/s

]

Z [cm]

(c) 30 MeV

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[ele

ctr

on/c

m2/s

]

Z [cm]

(d) 40 MeV

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[ele

ctr

on/c

m2/s

]

Z [cm]

(e) 50 MeV

Figure 3.12 – Electron fluence as a function of the penetration length z in [electron/cm2/s]with electron beams of different energies at an intensity I = 10 µA for BeO pellets of densityρ = 3.01 g/cm3 with a 0.8X0 converter.

32

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+11

1e+12

1e+13

1e+14

(a) 20 MeV, No biasing

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+11

1e+12

1e+13

1e+14

(b) 20 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+11

1e+12

1e+13

1e+14

(c) 30 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+11

1e+12

1e+13

1e+14

(d) 40 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+11

1e+12

1e+13

1e+14

(e) 50 MeV

Figure 3.13 – Photon fluence on the XZ plane in [photon/cm2/s] with electron beams of differentenergies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

33

1e+11

1e+12

1e+13

1e+14

-5 0 5 10 15 20 25

[ph

oto

n/c

m2/s

]

Z [cm]

(a) 20 MeV, No biasing

1e+11

1e+12

1e+13

1e+14

-5 0 5 10 15 20 25

[photo

n/c

m2/s

]

Z [cm]

(b) 20 MeV

1e+11

1e+12

1e+13

1e+14

-5 0 5 10 15 20 25

[photo

n/c

m2/s

]

Z [cm]

(c) 30 MeV

1e+11

1e+12

1e+13

1e+14

-5 0 5 10 15 20 25

[photo

n/c

m2/s

]

Z [cm]

(d) 40 MeV

1e+11

1e+12

1e+13

1e+14

-5 0 5 10 15 20 25

[photo

n/c

m2/s

]

Z [cm]

(e) 50 MeV

Figure 3.14 – Photon fluence as a function of the penetration length z in [photon/cm2/s] with elec-tron beams of different energies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3

with a 0.8X0 converter.

34

0 5 10 15 20 25 30 35

Pellet Number #

0.01

0.1

1

10

100

De

po

sit

ed

Po

we

r [W

]

20 MeV

30 MeV

40 MeV

50 MeV

Figure 3.15 – Deposited power per pellet with electron beams of different energies at an intensityI = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

20 30 40 50Beam Energy [MeV]

0

100

200

300

400

500

600

De

po

sit

ed

Po

we

r [W

]

Ta convertorBeO target

Total volume

Figure 3.16 – Deposited power per region as a function of the electron beam energy at an intensityI = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

35

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

(a) 20 MeV, No biasing

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

(b) 20 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

(c) 30 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

(d) 40 MeV

-5 0 5 10 15 20 25

Z [cm]

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X [

cm

]

1e+09

1e+10

1e+11

1e+12

1e+13

(e) 50 MeV

Figure 3.17 – Deposited power on the XZ plane in [W/cm3] with electron beams of different ener-gies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

36

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[W/c

m3]

Z [cm]

(a) 20 MeV, No biasing

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[W/c

m3]

Z [cm]

(b) 20 MeV

1e+09

1e+10

1e+11

1e+12

1e+13

-5 0 5 10 15 20 25

[W/c

m3]

Z [cm]

(c) 30 MeV

1e+10

1e+11

1e+12

1e+13

1e+14

-5 0 5 10 15 20 25

[W/c

m3]

Z [cm]

(d) 40 MeV

1e+10

1e+11

1e+12

1e+13

1e+14

-5 0 5 10 15 20 25

[W/c

m3]

Z [cm]

(e) 50 MeV

Figure 3.18 – Deposited power as a function of the penetration length z in [W/cm3] with electronbeams of different energies at an intensity I = 10 µA for BeO pellets of density ρ = 3.01 g/cm3

with a 0.8X0 converter.37

3.4 Conclusions

FLUKA simulations enabled us to study the photodisintegration of 9Be in great detail. First, an

optimal thickness for the converter was determined by comparing the impact on the produc-

tion rates for different sizes. Through this method, the converter optimal thickness was set to

0.8X0 = 0.328 cm. From simulations, the production rate obtained for 8Li shows that it would be

possible to have yields going up to 5.05× 108 pps (before diffusion of the ions) with an electron

beam of I = 10 µA at Ee = 50 MeV. From extrapolation of the present results, 8Li production

intensity would increase up to 4.38× 109 pps using the ARIEL electron beam at Ee = 25 MeV

and I = 4 mA (Phase III). A further increase of the beam power to Ee = 50 MeV, I = 10 mA would

enable to increase the 8Li production by a factor 100, to 5.05× 1011 pps.

Next, the length of the BeO target was optimized for 8Li ion production taking into account the

geometry of the target oven at Orsay. Considering the 8Li production rate per pellet and the power

dissipated as a function of the penetration depth into the target, it was presented that it could be

beneficial for ion production to use a half-length target (17 pellets) due to condensation caused

by steep temperature gradients within the target. With a reduction of the length, the effect of the

temperature gradient would be much less important and the 8Li yield would be reduced by only

11%, to 4.52× 108 pps. That is at one condition, that we can extract the power deposited into

the converter and the target material efficiently. This deposited power in the Ta converter could

reach 103.93 W with the beam power of Orsay. Without a cooling system, the power deposited

during the 100 kW phase of ARIEL would be of the order of 41.16 kW, and of 103.93 kW during

the 500 kW phase.

While running such simulations, biasing techniques are important in order to improve statistics

and computing time. On the other hand, the biasing applied must be fine tuned so that the results

are still reliable within these better statistics. By comparing the results with and without biasing at

20 MeV, where the statistics are the fewest, it was shown that the results were sufficiently similar.

This assures that biasing could be used in all other energy ranges as the % error between biased

and unbiased results would only decrease as the beam energy was increased.

38

Target Material

The production target is manufactured in house at TRIUMF, designed to fit the tantalum target

oven and graphite container that are used at Orsay. The target, composed of beryllium oxide

(BeO), consists of pellets that are 2 to 6 mm thick with a diameter of approximately 14 mm.

The pellets fabrication steps are as follows :

� a binder is mixed with the BeO powder,

� the BeO powder is reduced to fine granules using a ball mill apparatus,

� the mixture is compressed into pellets using a press, and

� the pellets are brought to 1600°C to remove the polymers used in the binder.

A casting procedure also has been developed and it is discussed in section 4.2.

An important goal in the target development is the reduction of outgassing from the target material

on-line. Therefore, the degassing rate of the target pellets as a function of current (temperature)

must be monitored closely. Additionally, sufficient strength of the pellets after the degassing phase

must be insured to survive not only their use on-line, but also the physical shipment process from

Vancouver, Canada to Orsay, France.

During the production, some pellets are examined using an electron microscope to determine the

size of the granules. Such examination of the sintered pellets allows an optimal treatment of the

powder to be found in order to optimize the grain size that makes the diffusion and effusion of the

ions produced faster. The goal of the optimization is to reach an average size of 5 to 10 microns.

Finally, upon exiting the evaporator after the sintering step, the pellets are observed to undergo

reduction in size compared to their original size after compacting. Adjustments of the initial di-

mensions of the pellets are necessary to make certain the final dimensions of the sintered pellets

fit the graphite target container of Orsay.

39

4.1 Casting

Beginning with the most promising recipe from the work accomplished in 2009 [19], an aqueous

solution on lubricated Teflon baking ware was made :

20 g BeO powder (American Beryllia Inc. 99.5% BeO)

20 ml (100%) deionised (D.I.) H2O as solvent

0.8 g (4%) Ammonium citrate as dispersant

Milled at 120 RPM for 3 minutes, with 8 ZrO2 balls in 250 ml ZrO2 jar

Add 20 ml (total 200%) D.I. H2O

Milled at 120 RPM for 3 minutes

Milled at 60 RPM overnight (∼18 hours)

2 g (10%) PEG 400 as plasticizer

2 g (10%) Glycerol as plasticizer

8.65 g (43%) 10% Polyvinyl alcohol (PVA) solution as binder

2 ml Butanol as surfactant

1.5 ml Methanol as surfactant

Pre-mixed solution in a beaker

Milled at 60 RPM for ∼3 hours

Cast on greased, with PAM Butter Flavor, Teflon baking ware.

Here, the cooking spray flavour is specified since the different flavours are composed of different

ingredients. As this procedure was still at a research and development phase, the goal of using

PAM was simply to find an easy way to make the cast not stick. After drying, the cast was heavily

cracked though it was not stuck to the baking ware. A second cast was made on non-greased

baking ware which was covered with paper towels. This allowed the cast to dry more slowly which

prevented significant cracking. These casts are shown on Figure 4.1. The dried cast showed few

cracks and also was not stuck to the baking ware. Neither casts cracked more when punched.

(a) (b)

Figure 4.1 – BeO casts which were (a) uncovered and (b) covered during the drying process.

40

Table 4.1 – Characteristics of the BeO disks punched from the first cast recipe

SampleMass (g)± 0.0001

Thickness (mm)± 0.001

Density (g/cm3)

1 0.1145 0.610 1.161 ± 0.0042 0.1243 0.635 1.210 ± 0.0043 0.115 0.620 1.147 ± 0.0044 0.0855 0.455 1.162 ± 0.0055 0.1066 0.575 1.146 ± 0.0046 0.0898 0.408 1.361 ± 0.0067 0.1023 0.566 1.118 ± 0.0048 0.1085 0.580 1.157 ± 0.0049 0.1091 0.575 1.173 ± 0.00410 0.1199 0.631 1.175 ± 0.00411 0.0781 0.378 1.278 ± 0.006

Average 0.1049 ± 0.0147 0.548 ± 0.091 1.182 ± 0.071

The measurements done on the second set of casts, punched from non-cracked areas with a 14

mm puncher, are listed in Table 4.1.

The next try included a high speed treatment of the BeO powder as well :

10 g BeO powder

40 ml (400%) D.I. H2O as solvent

Milled at 400 RPM for 26 minutes (2 min/rep, 3 min pulsing),

with 8 ZrO2 balls in 250 ml ZrO2 jar

0.4 g (4%) Ammonium citrate as dispersant

Milled at 60 RPM overnight

1 g (10%) PEG 400 as plasticizer

1 g (10%) Glycerol as plasticizer

8.65 g (43%) 5% PVA solution as binder

2 ml Butanol as surfactant

1.5 ml Methanol as surfactant

Pre-mixed solution in a beaker

Milled at 60 RPM for 3 hours

Cast on greased, with PAM Butter Flavor, Teflon baking sheet, covered with metal plate.

The dried cast looked smooth, however it was stuck to the plate. This seemed to be due to the

solvent being too diluted. The cracks, which appeared during drying, suggest that the dispersant

was insufficient [10]. In other words, the ammonium citrate was not strong enough to overcome the

hydrogen bonds of the water. One could suggest using a non-aqueous solvent, such as acetone

or trichloroethylene, but the production and cleaning become much more unkempt.

41

Instead of going down the non-aqueous route, an aqueous solution with a stronger dispersant

agent, albumin from egg whites, was used :

10 g from the previous dried cast

12 ml 10% Ammonium Hydroxide (NH4OH)

5 ml Albumin from egg white as dispersant

2 ml Butanol as surfactant

1.5 ml Methanol as surfactant

Milled at 60 RPM for 3 hours, with 8 ZrO2 balls in 250 ml ZrO2 jar

Cast on greased, with PAM Butter Flavor, large loaf pan.

No cracks were observed on the dried cast, yet the cast was difficult to remove from the pan. With

these results in hand, this recipe appears to be on the right track and would have been studied in

more details if an even more promising track had not been introduced : dry pressing.

4.2 Pressing

A 14-mm diameter press die composed of four parts was machined from aluminum and brass by

the mechanical technician and is shown in Figure 4.2. The manual press used, also shown in Fi-

gure 4.2, has a maximum capacity of 1 ton. Given the powder spreading hazard of the procedure,

the first pressing tests were done with silicon carbide (SiC) and aluminum oxide (Al2O3) to limit

the hazard of exposure to the toxicity of BeO powder.

The first pellets were made of SiC and Polyvinyl butyral (PVB). After compressing, the powder

held together nicely. When heated in the furnace under air atmosphere, the SiC/PVB pellets

(a) (b)

Figure 4.2 – (a) 14-mm diameter press die and (b) 1-ton manual press used to make BeO pellets.

42

stayed together, although fell apart when extracted using forceps.

Next, an Al2O3 powder was pressed. Nevertheless, it was still difficult to find the right binder to

use in combination with the right concentration necessary to hold the pellet together. It was found

that 10% weight/weight PVB was not enough, neither was 20%. Finally a 30% PVB in Al2O3

powder was found sufficient for the pellet pressing tests. After sintering at 400°C in the furnace,

the pellets were holding together though still very brittle. The poor structure of the samples was

suspected to be caused by the direct heating at high temperature. Specifically, all the organic

substances evaporate during heating. If the temperature change is too sudden, all molecules

needed for binding escape the pellet, leaving nothing to hold the structure together. A slower

heating process was applied with the next samples and found to improve the situation. Then the

following recipe was tested :

5.19 g Al2O3 powder

1.64 g ( 30%) PVB

5 ml Acetone

Mixed in mortar until it turns to tiny couscous-like grains/powder

Pressed ∼1 g mixed powder in die.

The samples were heated in a tantalum boat at 200◦C for 1.5 hour. The pellets colour changed

from white to dark yellow, and later to an orange shade shown in Figure 4.3. Following this recipe,

the samples could be handled without causing them to break. The heating process went on at

300◦C for 45 minutes. All samples progressed through the reaction by turning black. The same

pellets were heated at 400◦C for 25 minutes with no visible change observed. Heating was conti-

nued for 15 minutes at 500◦C. The pellets ultimately turned white again around 480◦C, still the

samples appeared quite fragile. These different colour stages which occurred during heating are

indications of chemical reactions happening as the organic additives are burned out.

The same procedure was followed with BeO powder, 30% PVB along with excess acetone as a

solvent. The mixture was milled and ground in a mortar until the acetone evaporated and larger

grains were left. One gram of mixture was put in the die and pressed for about 15 seconds.

The pellet characteristics are listed in Table 4.2. The average diameter before sintering was

14.35 ± 0.034 mm. One can see that the thickness and mass measurements are vastly more

regular than achieved using the punched casts (Table 4.1).

Sintering took place within an evaporator under vacuum which allows progressive heating and

cooling. As shown in Figure 4.4a, the pellets were loaded on a tantalum target boat, which itself

was wrapped with a layer of 50 µm thick Ta foil. The foil acted as a heat shield, reflecting the shine

of the heated boat increasing the temperature inside the boat. After sintering at up to 1000°C, the

four BeO pellets shrunk and were quite robust. The sintered pellets are shown here in Figures

4.4b. They could be manipulated with tweezers or by hands without breaking. Further tests of

their robustness were performed by dropping them from a few centimetres, and they also passed

43

(a) Green pellets before sintering (b) Pellets after heating at 200◦C for 1.5 hour

(c) Pellets after heating at 300◦C for 45 additional minutes (d) Pellets after heating at 400◦C for 25 additional minutes and500◦C for 15 additional minutes

Figure 4.3 – Chemical reactions showing as colour variations during the sintering in furnace ofAl2O3 pellets pressed from 30% w/w PVB and Al2O3 powder washed with acetone.

Table 4.2 – Characteristics of the BeO pellets batch #1 (pressed from 30% w/w PVB and BeOpowder washed with acetone) before and after sintering

Before sintering After sintering

SampleMass (g)± 0.0001

Thickness(mm)± 0.001

Density(g/cm3)± 0.001

Mass (g)± 0.0001

Thickness(mm)± 0.001

Diameter(mm)± 0.001

Density(g/cm3)

1 0.9628 4.943 1.204 0.7118 3.688 11.231 1.948 ± 0.0032 0.9685 4.930 1.215 0.7196 3.822 11.241 1.897 ± 0.0023 0.9607 4.758 1.248 0.7037 3.810 11.188 1.879 ± 0.0024 0.9872 4.979 1.226 0.7077 3.803 11.269 1.866 ± 0.002

Avg. 0.9698 4.903 1.223 0.7107 3.781 11.232 1.897±0.0121 ± 0.099 ± 0.019 ± 0.0068 ± 0.054 ± 0.034 ± 0.036

Average gain-0.2591

(-26.72%)-1.122

(-22.88%)-3.118

(-21.73%)0.6740

(+55.10%)

44

(a) Four green BeO pellets in Ta boat in the evaporator

(b) Sintered BeO pellets (c) EPICS Archive screen capture, with vacuum pressure in red (left-handscale), current in green (right-hand scale) and voltage in blue

Figure 4.4 – Sintering of BeO pellets batch #1 pressed from 30% w/w PVB and BeO powderwashed with acetone.

by not breaking. During the sintering process, one of the pellets rolled to the extremity of the target

boat tube and still had black traces from incomplete sintering on one side. It is interesting to note

that 27% of the mass was lost during sintering while we added 30% w/w of PVB. Therefore, most

of the PVB was burnt out. Finally, the average density after sintering was 1.897 ± 0.036 g/cm3.

When compared to the density of BeO, 3.01 g/cm3 [18], the pellets have 63% of the density of

BeO.

The parameters recorded during the sintering process were plotted and presented here in Figure 4.4c.

The red curve in the figure is the vacuum pressure (with scale on the left) while the green curve is

the current (with scale on the right) and the blue curve is the voltage (scale not shown). The power

supply was used in current limiting mode which allowed the heating temperature to be controlled

through the current applied to the target boat. Even though there were no thermocouples avai-

lable at the time to measure the temperature of the boat directly, the temperatures were measured

with an analogue pyrometer through three holes previously punched in the Ta wrapping foil. One

can see from the EPICS screen capture that the vacuum pressure raises with the current until it

reaches the preset maximum value at which time the current is ramped down until the vacuum

comes back into the predetermined range. The auto-ramping settings were : 1 A/min, up to 500 A,

between 5.00× 10−5 and 6.00× 10−5 Torr. The oscillations observed in the vacuum are due to

45

(a) Green (200 microns, x200) (b) Sintered top surface (50 microns, x800)

Figure 4.5 – SEM pictures on BeO pellets batch #1 pressed from 30% w/w PVB and BeO powderwashed with acetone.

organic additives burning out, or outgassing, during the process. When the organics are done

outgassing, the current and voltage are free to increase at a faster rate without a significant effect

on the chamber pressure. Collectively, this is the so-called sintering process.

Figure 4.5 was taken with a scanning electron microscope (SEM). The SEM pictures of the first

BeO pellets show that the pellets were not fully sintered. One can see that there are still large

chunks of material, large grains and large pores. A more homogeneous surface, with many smal-

ler pores, is preferred in order to facilitate the release of produced atoms. Thus while a high

density in beryllium allows for a good production rate, a good release rate can be achieved by

also having a high porosity. If the porosity is not sufficient, atoms will still be produced though

unable to leave the target. Further, on the scan, white particles are observed which are unders-

tood to be contaminants. Analysis with energy-dispersive X-ray spectroscopy (EDX) and powder

diffraction were performed as well on the next set of pellets and are discussed later.

In an effort to replace the milling by hand with the mortar, the next mixture of BeO powder and

30% PVB washed with excess acetone was left to dry on a Teflon sheet. Unfortunately this dried

mixture stuck to the baking sheet. The procedure was repeated on a Teflon sheet greased with

butter flavored PAM cooking spray. When the acetone evaporated, the mixture cracked into flakes.

The flakes were then placed in a 250 ml ZrO2 jar with 8 ZrO2 balls and milled at 400 RPM for

26 minutes (2 min/rep, 3 min pulsing). This process resulted in a very fine grey powder having

a wet sand texture. Two pellets were pressed from that grey powder. A third pellet was pressed

from BeO powder and 30% PVB not washed with acetone. The first powder, used for Samples

#1 and #2, was much denser than the second powder used for Sample #3. All samples showed

a large amount of residue from oxidation of the die. Table 4.3 lists the measurements from pellets

in batch #2. The average mass measurements listed do not include the third sample.

46

Table 4.3 – Characteristics of the BeO pellets batch #2 (pressed from 30% w/w PVB and BeOpowder washed with acetone on a greased Teflon sheet) before and after sintering

Before sintering After sintering

SampleMass (g)± 0.0001

Thickness(mm)± 0.001

Density(g/cm3)± 0.001

Mass (g)± 0.0001

Thickness(mm)± 0.001

Density(g/cm3)

1 1.9713 9.06 1.345 0.6254 - -2 1.9900 9.11 1.351 0.9229 5.81 1.03

3 (no acetone) 1.9916 13.54 0.909 1.1073 8.89 0.81Average 1.9843 ± 0.0142 - - 0.8852 ± 0.2625 - -

Average gain-1.2065

(-60.91%)- -

(a) BeO samples #1, #2 and #3 after sintering

(b) Hole in Ta target boat after reacting with the BeO samples (c) Damaged Ta target boat in the evaporator after sintering

Figure 4.6 – Reaction between the Ta target boat and the target material during the sintering ofBeO pellets batch #2 (pressed from 30% w/w PVB and BeO powder washed with acetone on agreased Teflon sheet).

47

After sintering, the three BeO pellets again had shrunk and felt rugged. The first sample destroyed

the Ta target boat, had greater shrinking and white and black marks as seen on Figure 4.6. It is

suspected that the cooking spray (mostly made of canola oil) is responsible for the boat damage

along with an unstable vacuum observed during the sintering process. Sample #2 was holding

well and kept the grey colour of the powder used. Sample #3, which was not washed with acetone,

showed some cracks. As shown in Figure 4.6c, the Ta foil also reacted causing residues to deposit

on the copper heat shield.

These samples were sintered in the evaporator while being ramped up at 1 A/min, to a maximum

current of 750 A. The maximum voltage during sintering was limited to 14 V, with a vacuum

between 5.00× 10−5 and 6.00× 10−5 Torr. During this process, the pressure did drop as low as

10−6 Torr and was not stable. The fluctuation in the vacuum is suggesting that some reaction was

ongoing and most likely causing vacuum excursion. As seen in Figure 4.7, the current read back

was not constant, with the voltage read back increasing faster than the current. From Ohm’s law

(V = R I), this is a sign of an increasing resistance which means that the boat is reacting with

the pellets or an outgassing substance. Cooling down proceeded at 2 A/min.

The SEM pictures of the BeO pellets from Sample #2 are shown in Figure 4.8. Again, because

the grains are not fully fused together, the sample is observed to have not been fully sintered.

Nevertheless, the pores and the grain size are smaller and show a more homogeneous distribu-

tion. These pictures show very interesting results which should provide a good environment to

stimulate ion release. As with the last SEM pictures, the white spots are contaminants. Though

it should be noted that the contaminants are less abundant on the inside of the pellet than on its

surface or side. Again, this suggests that the oxidation from the die is significant.

Table 4.4 shows the results of the energy-dispersive X-ray spectroscopy (EDX). These results are

qualitative and do not show the concentration of beryllium. The observed zirconium (Zr) came

from the ZrO2 balls and jar while observed silicon (Si) and carbon (C) most probably came from

cross contamination while working with SiC in the same fume hood used to prepare the BeO

samples. Though some carbon must also have come from the press die and the tantalum, which

came from the target boat and heat shield.

Finally, an X-ray powder diffraction analysis was performed as well on several samples. The re-

sults, shown in Figure 4.9, confirmed that BeO is the main component without showing any si-

gnificant contaminant. The red peaks in Figure 4.9 are the unique chemical fingerprint of BeO

and correspond perfectly to the peaks observed in black, from the samples. One can see that the

background of the histogram is much smoother in the sintered sample than in the powder treated

at high speed, since other molecules were burnt out.

In an effort to spare further damage to more thousand-dollar tantalum boats, the next batch of

BeO + 30% PVB powder was washed with excess acetone and left to dry on a non-greased

baking sheet. The dried cast stuck on the sheet was lifted off using more acetone. The resulting

48

(a) Vacuum excursions at 700 A

(b) Vacuum excursions at 750 A

Figure 4.7 – EPICS screen captures of a reaction between the Ta target boat and the targetmaterial during the sintering of BeO pellets batch #2 (pressed from 30% w/w PVB and BeOpowder washed with acetone on a greased Teflon sheet), with vacuum pressure in red, current inbrown (left-hand scale) and voltage in green).

49

(a) Top surface (200 microns, x200) (b) Inside (200 microns, x200)

(c) Side (200 microns, x200) (d) Side (50 microns, x800)

Figure 4.8 – SEM pictures on sintered BeO pellets batch #2 pressed from 30% w/w PVB and BeOpowder washed with acetone on a greased Teflon sheet.

Table 4.4 – Energy-dispersive X-ray spectroscopy (EDX) on BeO pellets batch #2 pressed from30% w/w PVB and BeO powder washed with acetone on a greased Teflon sheet [Performed atthe UBC X-ray Crystallography facility]

Element Concentration 2 SigmaC 2.77 at% 0.472 at%N 7.38 at% 1.934 at%O 87.59 at% 1.195 at%Si 0.07 at% 0.152 at%Zr 1.15 at% 0.037 at%Ta 1.05 at% 0.072 at%

flakes were treated at 400 RPM for 26 minutes (3 minutes pausing). After treatment, the very fine

dry white powder was pressed as before. The samples left residue and felt like chalk. The sides

50

(a) Treated powder (400 RPM)

(b) Sintered pellet

Figure 4.9 – Powder diffraction analysis on BeO pellets batch #2 pressed from 30% w/w PVBand BeO powder washed with acetone on a greased Teflon sheet. [Performed at the UBC X-rayCrystallography facility]

51

of the sample were easily chipped. The sample was obviously missing something that was in the

previous recipe using non-stick cooking spray. Instead of trying another PAM flavour for which the

recipe is unknown, the next procedure involved mineral oil :

10 g BeO + 30% PVB powder

High speed treatment at 400 RPM for 26 minutes (2 min/rep, 3 min pulsing),

with 8 ZrO2 balls in 250 ml ZrO2 jar

10% Mineral oil

Milled at 400 RPM for 10 minutes (2 min/rep, 3 min pulsing)

Pressed ∼1.3 g mixed powder in die.

Much like the previous recipe, the powder had a nice wet sand texture, as desired. The pel-

lets were loaded on a target boat previously coated and sintered with tantalum carbide (TaC),

wrapped with a Ta foil which was again 50 µm thick. The chamber was pumped down, but sinte-

ring was postponed due to ventilation issues. The sintering process was started 48 days later at

1 A/min, up to 750 A, with the maximum voltage limited to 15 V and a vacuum of 3.00× 10−5 to

4.00× 10−5 Torr. Three days later, a power failure caused the target heater (TGHT) power supply

to trip off, as seen in Figure 4.10. The TGHT was reset and stayed at 600 A for about 12 hours

before a water leak was discovered from the evaporator chiller. At 600 A, the target boat tempe-

rature was measured to be 1400◦ C (with the pyrometer) while the Ta heat shield was at 1050◦

C. The target was cooled down for about 20 minutes and the evaporator chamber was vented.

(a) EPICS Archive screen capture, with vacuum pressure in green (right-hand scale) andcurrent in red (left-hand scale)

(b) Cracked BeO pellets

Figure 4.10 – Power failure during the sintering of BeO pellets batch #3 pressed from 30% w/wPVB, mineral oil and BeO powder.

52

The six pellets were cracked and had a greyish colour. The cracking was probably caused by

the instant cooling and reheating when the system tripped. The light grey colour and white spots

suggest that the sintering process was not completed and so the shrinkage cannot accurately be

determined. Therefore a new batch of BeO pellets has to be prepared and sintered in order to

determine the dimensions of the final die.

Further attempts were also carried out to try and finally determine the amount of shrinkage of the

pellets during sintering process. However, during the sintering of batch #4, the Ta boat reacted

violently with the BeO pellets as shown in Figure 4.11. A Ta foil coated and sintered with TaC was

placed along the inside of the target boat which was already weakened due to previous sintering

procedures. The EPICS archive shows how the resistance increased until the boat broke and

the current could no longer flow. An attempt was made to raise the current again but failed. The

chamber was left to cool and then vented. The resulting pellets were burnt and unusable.

(a) Broken Ta target boat wrapped with a Ta foil afterit reacted with the BeO pellets during the sinteringprocess

(b) Burnt pellets which reacted with the Ta targetboat during the sintering process

(c) EPICS Archive screen capture, with vacuum pressure in pink, current in red (left-hand scale)and voltage in green (right-hand scale)

Figure 4.11 – Reaction between the Ta target boat and the target material during the sintering ofBeO pellets batch #4 pressed from 30% w/w PVB, mineral oil and BeO powder.

53

Finally a preliminary test was conducted using a rhenium (Re) foil underlayer (50 µm thick) to try to

prevent the reaction between beryllium and the tantalum boat, instead of the TaC coated tantalum

foil. This underlayer is shown here in Figure 4.12. Another layer of Ta foil was still used as the

heat shield wrapped around the entire boat. The rhenium was suggested by a senior chemist at

TRIUMF who remembered using tungsten to protect from calcium [20]. With rhenium being right

next to tungsten in the periodic table, and calcium sharing the same group with beryllium, the

suggestion sounded promising. The boat survived the sintering process and further tests should

study this avenue of approach.

(a) Alkaline earth metals and 6th period(www.elementsdatabase.com)

(b) Rhenium underlayer on Ta boat with three green BeO pel-lets

Figure 4.12 – Sintering of BeO pellets batch #5 pressed from 30% w/w PVB, mineral oil and BeOpowder.

54

4.3 Conclusions

The BeO target is sintered at TRIUMF in order to reduce the outgassing of the target material

during on-line isotope production at Orsay ALTO. The pressing technique with 30% w/w PVB

and 10% w/w mineral oil results in a much smoother sintering process as there are not as many

organic additives as seen with the casting technique.

This recipe results in very rugged pellets after degassing and sintering. By protecting the boat

with a rhenium foil, we could reach even higher sintering temperatures, increasing the fusion of

the grains for a more robust structure.

The final density and the shrinkage of the pellets caused by the sintering process still needs to

be determined more accurately. Unfortunately, work required to fix the ventilation issues in the

laboratory, which delayed the sintering of the BeO pellets batch #3, prevents the current work

from accomplishing this task. Adjustments to the pressing die shall be made so that the final

dimensions of the sintered pellets fit the graphite target container of Orsay, which has an inside

diameter of 14 mm.

Future laboratory tests could take advantage of the newly acquired chemistry instruments. In-

deed, a residual gas analyser (RGA) could provide valuable information about the outgassing

products, while thermocouples (Type C) would enable close monitoring of the temperature rather

than relying on the current applied and pyrometer measurements.

55

Preliminary Tests

The next step, once the pellet fabrication is completed, is to evaluate the proposed concept on-line

and to study the release rate of radioactive atoms from the BeO target using the linear electron

accelerator at IPN Orsay, ALTO. We want to extract the production rate of 8Li and its average

release rate. For the first test, there will be a converter placed directly in front of the BeO target

similar to the ARIEL 100 kW phase.

An initial test performed at Orsay in December 2010 has demonstrated the production of 8Li

using a BeO target. Along with the results from this first test, the new Monte Carlo simulations

performed using FLUKA enable us to obtain better estimates of the energy deposition in the target

and the production rate of rare isotopes. Furthermore, the improved target material reduces the

outgassing considerably.

Testing of the BeO target will allow us to determine the extraction efficiency of the radioactive

atoms produced in the interactions. In the case of 8Li, we know the ionization efficiency of the Li

using a hot surface ion source. Once production yields are established, we can compare them

with the ones estimated by FLUKA to extract the overall release efficiency from the BeO target.

In addition, we can pulse the ATLO electron beam to study the release speed of 8Li. We will use a

technique similar to the studies that were conducted with rubidium and cesium at Orsay Tandem

[21]. In this experiment, the Orsay Tandem team used a pulsed beam on a uranium target to

generate Rb and Cs isotopes. The Rb and Cs were ionized by surface ionization source, which

is nearly 100% effective for this type of elements. The intensity of the isotope 91Rb was recorded

versus time. Using the method of least squares, we can make an adjustment of the signal and

extract the rate of production and the release time of this isotope from the target.

57

5.1 Results from 2010

Figure 5.1 shows the 8Li production rates obtained with a 10 µA electron beam in December

2010. This initial test was conducted with no absorber before the target material and with high

outgassing of the target material. Considering an intensity of 10 µA, we get a production rate of

9.61× 10−9 ion/e- at 50 MeV. Comparing with Figure 3.6, where we obtained 6.37× 10−6 ion/e-

at the same energy with a 250 microns thick converter and a BeO density of 3.01 g/cm3, we find

that the release efficiency of the target was 0.15%. These values are similar to release rates

generally obtained. The loss in production is attributed to the diffusion and effusion of the atoms

through the target, and the ionization and transport of the ions.

Figure 5.1 – 8Li production rates [y-axis in pps] as a function of the electron beam energy [x-axisin MeV] obtained at ALTO Orsay at an intensity I = 10 µA in December 2010 with a previous BeOtarget and a 250 micron thick Ta converter. [22]

58

Conclusion

The commissioning of ARIEL consists in the study of photodisintegration of a BeO target with an

electron beam. This mechanism will be used to produce its first radioactive beams through the

reaction 9Be(γ,p)8Li.

The modelling of this reaction, by means of Monte-Carlo simulations, can help determine pre-

cisely which parameters should be optimized in the chemistry laboratory and in the machine

shop in order to reach optimal RIB production. Some results obtained with FLUKA, presented

within this thesis, showed that using a tantalum converter with an optimum thickness of 0.328 cm,

5.05× 108 pps of 8Li can be produced with an electron beam of Ee = 50 MeV and I = 10 µA. It

was demonstrated that using a half-length target, the 8Li yield would suffer a reduction of only

11% (i.e. to 4.52 x 108 pps). This would represent a 8Li production intensity of 109 pps using an

ARIEL electron beam of Ee = 25 MeV at I = 4 mA (Phase III). Furthermore, it was shown that 8Li

RIB production could be increased by two orders of magnitude by increasing the incident beam

power to 500 kW (i.e. Ee = 50 MeV at I = 10 mA).

The manufacturing of the BeO target for the production of 8Li is a challenging procedure. The

reduction of the target material outgassing on-line and the strength of the sintered pellet are just

a few of the difficulties one needs to overcome to produce a high quality target. Both issues

were shown here to be resolved using a pressing technique of BeO powder with 30% w/w PVB

and 10% w/w mineral oil. This method results in a smoother sintering process which yields very

rugged pellets with homogenous porosity. By protecting the sintering boat with a rhenium foil,

even higher sintering temperatures can be reached, which consequently increases the fusion of

the grains for a more robust structure. The shrinkage of the pellets still needs to be determined

more accurately and the pressing die adjustments need to be made accordingly. This is an issue

that must not only be addressed for the pellets that would be used for the Orsay target container

but also with the new target design for ARIEL.

Finally the evaluation of the constructed target on-line at ALTO Orsay provides means to bench-

mark previous simulations. From the first casting recipe, a 8Li yield of 5.98× 105 pps was measu-

red from a 50 MeV, 10 µA electron beam in December 2010. The release efficiency of the target

was then of 0.12%. By using an optimized converter with the newly developed and optimized tar-

get, the beam production would certainly be increased while the outgassing of the target material

59

would most definitely be greatly decreased.

The next step is to design the target/ion source assembly with a tantalum converter for the third

phase of the ARIEL project, taking into account the results of the tests performed at Orsay. This

target assembly would also be implemented with the uranium carbide (UCx) targets. For this

100 kW phase of ARIEL, the overall thermal conductivity of the target is increased by manufac-

turing composite target materials such as BeO/Nb and UCx/graphite. This procedure was deve-

loped at ISAC and has proven to be successful when incident beam powers in the order of 12.5

kW are applied. With this process, it would be very informative to compare the release efficiency

of rare isotopes from the composite target to the pure oxide ones. One last future objective is

the design of the target/ion source with a molten lead converter, which is currently planned to be

implemented for ARIEL during the 500 kW phase.

60

Appendix A

FLUKA Input File

TITLE

BeO target

* Set the defaults for precision simulations

DEFAULTS PRECISIO

*

* - - - - PRIMARY - - - -

*

* Beam definition

* If 20 MeV is set, then the 20 MeV e- beam is used.

#define 20MeV

#define 30MeV

#define 40MeV

#define 50MeV

#if 20MeV

* Define the beam characteristics :

* 20 MeV e- beam (10 mA).

BEAM -0.02 0.01 0.01 0.5 -1.0ELECTRON

#elif 30MeV

BEAM -0.03 0.01 0.01 0.5 -1.0ELECTRON

#elif 40MeV

BEAM -0.04 0.01 0.01 0.5 -1.0ELECTRON

#elif 50MeV

BEAM -0.05 0.01 0.01 0.5 -1.0ELECTRON

#endif

* Define the beam position :

* Start the beam at (0, 0, -0.5), in direction of +z axis.

BEAMPOS 0.0 0.0 -0.5 0.0 0.0

*

* - - - - GEOMETRY - - - -

*

GEOBEGIN COMBNAME

61

0 0 BeO target

* Black body

SPH blkbody 0.0 0.0 0.0 500.0

* Void sphere

SPH void 0.0 0.0 0.0 100.0

* Target oven

ZCC OVENout 0.0 0.0 1.05

ZCC OVENin 0.0 0.0 1.00

* container

ZCC INCYLout 0.0 0.0 0.95

ZCC INCYLin 0.0 0.0 0.75

* Target

ZCC TARGET 0.0 0.0 0.7

* Encaps

ZCC ENCAPS 0.0 0.0 1.15

* Start target

XYP targstar 0.0

* End target

XYP targend 20.2

* Right over endcap

XYP overrig 20.1

* Right endcap

XYP encaprig 20.5

* Left graphite endcap

XYP grendle1 0.3

XYP grendle2 0.5

* Right graphite endcap

XYP grendri1 19.5

XYP grendri2 19.7

XYP grendri3 20.0

* Individual BeO pellets, average thickness = 0.55 cm

XYP pellet1 1.05

XYP pellet2 1.60

XYP pellet3 2.15

XYP pellet4 2.70

XYP pellet5 3.25

XYP pellet6 3.80

* [ Region biasing plane 1 ]

XYP pellet7 4.35

XYP pellet8 4.90

XYP pellet9 5.45

XYP pellet10 6.00

XYP pellet11 6.55

XYP pellet12 7.10

62

XYP pellet13 7.65

* [ Region biasing plane 2 ]

XYP pellet14 8.20

XYP pellet15 8.75

XYP pellet16 9.30

XYP pellet17 9.85

XYP pellet18 10.40

XYP pellet19 10.95

XYP pellet20 11.50

* [ Region biasing plane 3 ]

XYP pellet21 12.05

XYP pellet22 12.60

XYP pellet23 13.15

XYP pellet24 13.70

XYP pellet25 14.25

XYP pellet26 14.80

XYP pellet27 15.35

* [ Region biasing plane 4 ]

XYP pellet28 15.90

XYP pellet29 16.45

XYP pellet30 17.00

XYP pellet31 17.55

XYP pellet32 18.10

XYP pellet33 18.65

XYP pellet34 19.20

* Left and Right Support Legs

XYP legz1 -0.3

* [ Left over endcap ]

XYP overlef 0.1

XZP legy1 -1.15

XZP legy2 1.15

YZP legx1 7.0

YZP legx2 -1.2

#define Conv1.2X

#define Conv1.1X

#define Conv1.0X

#define Conv0.9X

#define Conv0.8X

#define Conv0.7X

#define Conv0.6X

#define Conv0.5X

#define Conv0.4X

#define Conv0.3X

#define Conv0.2X

63

#define NoConv

#if Conv0.8X

* CONVERTER thickness = 0.8*X0 = 0.328 cm

XYP encaplef -0.328

#elif Conv1.1X

* CONVERTER thickness = 1.1*X0 = 0.451 cm

XYP encaplef -0.451

#elif Conv1.0X

* CONVERTER thickness = 1.0*X0 = 0.410 cm

XYP encaplef -0.410

#elif Conv0.9X

* CONVERTER thickness = 0.9*X0 = 0.396 cm

XYP encaplef -0.396

#elif Conv1.2X

* CONVERTER thickness = 1.2*X0 = 0.492 cm

XYP encaplef -0.492

#elif Conv0.7X

* CONVERTER thickness = 0.7*X0 = 0.287 cm

XYP encaplef -0.287

#elif Conv0.6X

* CONVERTER thickness = 0.6*X0 = 0.246 cm

XYP encaplef -0.246

#elif Conv0.5X

* CONVERTER thickness = 0.5*X0 = 0.205 cm

XYP encaplef -0.205

#elif Conv0.4X

* CONVERTER thickness = 0.4*X0 = 0.164 cm

XYP encaplef -0.164

#elif Conv0.3X

* CONVERTER thickness = 0.3*X0 = 0.123 cm

XYP encaplef -0.123

#elif Conv0.2X

* CONVERTER thickness = 0.2*X0 = 0.123 cm

XYP encaplef -0.082

#elif NoConv

* No CONVERTER, Foil thickness = 250 microns = 0.25 mm

XYP encaplef -0.025

#endif

END

#define Conv1.2X

#define Conv1.1X

#define Conv1.0X

#define Conv0.9X

#define Conv0.8X

64

#define Conv0.7X

#define Conv0.6X

#define Conv0.5X

#define Conv0.4X

#define Conv0.3X

#define Conv0.2X

#define NoConv

* Black hole

BLKBODY 5 +blkbody -void

* Void around

VOID 5 +void -OVENout -overlef +overrig | +void -encaprig

| +void -OVENout +legz1 | +void +OVENout +encaplef

| +void -legx1 | +void +legx2

|+void +legy1 | +void -legy2

* Void inside

VOIDin 5 +void +OVENin -INCYLout -targstar +targend

| +void +INCYLin -TARGET -grendle2 +grendri1

| +void +TARGET -pellet34 +grendri1 | +void +INCYLout -grendri3

+targend

* Left end cap + Leg

ENDCAPL 5 +ENCAPS -OVENout -legz1 +overlef

| +void -ENCAPS +legx1 -legx2 +legy2 -legy1 -legz1 +overlef

* Converter

CONVERTE 5 +OVENout -encaplef +targstar

* Right end cap + Leg

ENDCAPR 5 +ENCAPS +encaprig -targend | +ENCAPS -OVENout -overrig +targend

| +void -ENCAPS +legx1 -legx2 +legy2 -legy1 -overrig +encaprig

* Target oven

OUTCYL1 5 +OVENout -OVENin -targstar +pellet7

OUTCYL2 5 +OVENout -OVENin -pellet7 +pellet14

OUTCYL3 5 +OVENout -OVENin -pellet14 +pellet21

OUTCYL4 5 +OVENout -OVENin -pellet21+pellet28

OUTCYL5 5 +OVENout -OVENin -pellet28 +targend

* Container Endap Left

CENDCAPL 5 +INCYLout -targstar +grendle1 | +INCYLin -grendle1 +grendle2

* Container Endap Right

CENDCAPR 5 +INCYLin -grendri1 +grendri2 | +INCYLout -grendri2 +grendri3

* Container

INCYL1 5 +INCYLout -INCYLin -grendle1 +pellet7

INCYL2 5 +INCYLout -INCYLin -pellet7 +pellet14

INCYL3 5 +INCYLout -INCYLin -pellet14 +pellet21

INCYL4 5 +INCYLout -INCYLin -pellet21 +pellet28

INCYL5 5 +INCYLout -INCYLin -pellet28 +grendri2

* Target = Individual Pellets

65

PELLET1 5 +TARGET -grendle2 +pellet1

PELLET2 5 +TARGET -pellet1 +pellet2

PELLET3 5 +TARGET -pellet2 +pellet3

PELLET4 5 +TARGET -pellet3 +pellet4

PELLET5 5 +TARGET -pellet4 +pellet5

PELLET6 5 +TARGET -pellet5 +pellet6

PELLET7 5 +TARGET -pellet6 +pellet7

PELLET8 5 +TARGET -pellet7 +pellet8

PELLET9 5 +TARGET -pellet8 +pellet9

PELLET10 5 +TARGET -pellet9 +pellet10

PELLET11 5 +TARGET -pellet10 +pellet11

PELLET12 5 +TARGET -pellet11 +pellet12

PELLET13 5 +TARGET -pellet12 +pellet13

PELLET14 5 +TARGET -pellet13 +pellet14

PELLET15 5 +TARGET -pellet14 +pellet15

PELLET16 5 +TARGET -pellet15 +pellet16

PELLET17 5 +TARGET -pellet16 +pellet17

PELLET18 5 +TARGET -pellet17+pellet18

PELLET19 5 +TARGET -pellet18 +pellet19

PELLET20 5 +TARGET -pellet19 +pellet20

PELLET21 5 +TARGET -pellet20 +pellet21

PELLET22 5 +TARGET -pellet21 +pellet22

PELLET23 5 +TARGET -pellet22 +pellet23

PELLET24 5 +TARGET -pellet23 +pellet24

PELLET25 5 +TARGET -pellet24 +pellet25

PELLET26 5 +TARGET -pellet25 +pellet26

PELLET27 5 +TARGET -pellet26 +pellet27

PELLET28 5 +TARGET -pellet27 +pellet28

PELLET29 5 +TARGET -pellet28 +pellet29

PELLET30 5 +TARGET -pellet29 +pellet30

PELLET31 5 +TARGET -pellet30 +pellet31

PELLET32 5 +TARGET -pellet31 +pellet32

PELLET33 5 +TARGET -pellet32 +pellet33

PELLET34 5 +TARGET -pellet33 +pellet34

END

GEOEND

*

* - - - - MEDIA - - - -

*

* Beryllium oxide BeO

*

MATERIAL 3.01 BEO

COMPOUND 1.0 BERYLLIU 1.0 OXYGEN BEO

* Graphite

66

MATERIAL 6. 12.011 2.26 Graphite

LOW-MAT Graphite 6. -3. 296. CARBON

* Material assignments to regions

ASSIGNMA BLCKHOLE BLKBODY

ASSIGNMA VACUUM VOID VOIDin

ASSIGNMA TANTALUM ENDCAPL OUTCYL5

ASSIGNMA Graphite CENDCAPL INCYL5

ASSIGNMA BEO PELLET1 PELLET34

*

* - - - - PHYSICS - - - -

*

* Activates gamma interactions with nuclei

PHOTONUC 1. VACUUM @LASTMAT

PHYSICS 1. COALESCE

PHYSICS 3. EVAPORAT

*

* - - - - TRANSPORT - - - -

*

LOW-NEUT 260. 42. 0.02

* Set production threshold for e+, e- to 50 keV and photon to 10 keV in all

materials.

EMFCUT -5E-05 0.00001 VACUUM @LASTMAT PROD-CUT

* Set transport threshold for e+, e- to 50 keV and photon to 10 keV in all regions.

EMFCUT -5E-05 0.00001 VOID @LASTREG

* Activates single scattering.

MULSOPT 0.0 1. 1. GLOBAL

* Activation

RADDECAY 1. 1. 3.0 1000010

* Definition of irradiation profile : 10 days 10 microA = 6.24146E13 part/s

!@what.1=10*day

IRRPROFI 864000.0 6.2415E13

* Definition of decay times : -5 days 0.0 5 days 10 days 20 days 1 month

!@what.1=-5*day

!@what.3=5*day

!@what.4=10*day

!@what.5=20*day

!@what.6=1*month

DCYTIMES -432000.0 0.0 432000.0 864000.0 1728000.0 2629800.0

#define Flag_BIAS

#if Flag_BIAS

*

* - - - - BIASING - - - -

*

* Bias the decay length of unstable particles.

67

LAM-BIAS 0.02 PHOTON

* Leading particle biasing.

EMF-BIAS 1022. VOID @LASTREG LPBEMF

* Increasing region importances through target by factors of two.

* Importance 2 : 2 regions + 7 pellets + 2 endcaps + 1 converter

BIASING 0.0 1.0 2.0 ENDCAPL CONVERTE

BIASING 0.0 1.0 2.0 CENDCAPL

BIASING 0.0 1.0 2.0 OUTCYL1

BIASING 0.0 1.0 2.0 INCYL1

BIASING 0.0 1.0 2.0 PELLET1 PELLET7

* Importance 4 : 2 regions + 7 pellets

BIASING 0.0 1.0 4.0 OUTCYL2

BIASING 0.0 1.0 4.0 INCYL2

BIASING 0.0 1.0 4.0 PELLET8 PELLET14

* Importance 8 : 2 regions + 7 pellets

BIASING 0.0 1.0 8.0 OUTCYL3

BIASING 0.0 1.0 8.0 INCYL3

BIASING 0.0 1.0 8.0 PELLET15 PELLET21

* Importance 16 : 2 regions + 7 pelletsl

BIASING 0.0 1.0 16.0 OUTCYL4

BIASING 0.0 1.0 16.0 INCYL4

BIASING 0.0 1.0 16.0 PELLET22 PELLET28

* Importance 32 : 2 regions + 6 pellets + 2 endcaps

BIASING 0.0 1.0 32.0 OUTCYL5

BIASING 0.0 1.0 32.0 INCYL5

BIASING 0.0 1.0 32.0 PELLET29 PELLET34

BIASING 0.0 1.0 32.0 ENDCAPR

BIASING 0.0 1.0 32.0 CENDCAPR

#endif

*

* - - - - SCORING - - - -

*

* Beam particule fluence

USRBIN 10. BEAMPART -51. 2.0 2.0 22.0BeamPart

USRBIN -2.0 -2.0 -2.0 80. 80.0 240. &

* Electron fluence

USRBIN 10. ELECTRON -52. 2.0 2.0 22.0EleFlu1

USRBIN -2.0 -2.0 -2.0 80. 80.0 240. &

* Photon fluence

USRBIN 10. PHOTON -54. 2.0 2.0 22.0PhotFlu1

USRBIN -2.0 -2.0 -2.0 80. 80.0 240. &

* Cooling time for all detectors

DCYSCORE 2. EnDepAll USRBIN

* Energy deposition from All Particles

68

USRBIN 10. ENERGY -56. 2.0 2.0 22.0EnDepAll

USRBIN -2.0 -2.0 -2.0 80. 80.0 240. &

SCORE ENERGY

#define Flag_SCOR

#if Flag_SCOR

* Production rate per pellet in nuclei/primary

RESNUCLE 3. -62. 3. PELLET1 1.Resnuc1

RESNUCLE 3. -62. 3. PELLET2 1.Resnuc2

RESNUCLE 3. -62. 3. PELLET3 1.Resnuc3

RESNUCLE 3. -62. 3. PELLET4 1.Resnuc4

RESNUCLE 3. -62. 3. PELLET5 1.Resnuc5

RESNUCLE 3. -62. 3. PELLET6 1.Resnuc6

RESNUCLE 3. -62. 3. PELLET7 1.Resnuc7

RESNUCLE 3. -62. 3. PELLET8 1.Resnuc8

RESNUCLE 3. -62. 3. PELLET9 1.Resnuc9

RESNUCLE 3. -62. 3. PELLET10 1.Resnuc10

RESNUCLE 3. -62. 3. PELLET11 1.Resnuc11

RESNUCLE 3. -62. 3. PELLET12 1.Resnuc12

RESNUCLE 3. -62. 3. PELLET13 1.Resnuc13

RESNUCLE 3. -62. 3. PELLET14 1.Resnuc14

RESNUCLE 3. -62. 3. PELLET15 1.Resnuc15

RESNUCLE 3. -62. 3. PELLET16 1.Resnuc16

RESNUCLE 3. -62. 3. PELLET17 1.Resnuc17

RESNUCLE 3. -62. 3. PELLET18 1.Resnuc18

RESNUCLE 3. -62. 3. PELLET19 1.Resnuc19

RESNUCLE 3. -62. 3. PELLET20 1.Resnuc20

RESNUCLE 3. -62. 3. PELLET21 1.Resnuc21

RESNUCLE 3. -62. 3. PELLET22 1.Resnuc22

RESNUCLE 3. -62. 3. PELLET23 1.Resnuc23

RESNUCLE 3. -62. 3. PELLET24 1.Resnuc24

RESNUCLE 3. -62. 3. PELLET25 1.Resnuc25

RESNUCLE 3. -62. 3. PELLET26 1.Resnuc26

RESNUCLE 3. -62. 3. PELLET27 1.Resnuc27

RESNUCLE 3. -62. 3. PELLET28 1.Resnuc28

RESNUCLE 3. -62. 3. PELLET29 1.Resnuc29

RESNUCLE 3. -62. 3. PELLET30 1.Resnuc30

RESNUCLE 3. -62. 3. PELLET31 1.Resnuc31

RESNUCLE 3. -62. 3. PELLET32 1.Resnuc32

RESNUCLE 3. -62. 3. PELLET33 1.Resnuc33

RESNUCLE 3. -62. 3. PELLET34 1.Resnuc34

#endif

* Total production rate in nuclei/primary

RESNUCLE 3. -63. @ALLREGS 1.0ResNuc_0

* Residual nuclei after 5 days of cooling

69

DCYSCORE 3. ResNuc_5 RESNUCLE

RESNUCLE 3. -64. @ALLREGS 1.0ResNuc_5

* Set the random number seed

RANDOMIZ 1.

* Set the number of primary histories to be simulated in the run

START 50000.

STOP

STOP

70

Appendix B

Isotope Production Rates

71

Table B.1 – Production rates of different isotopes during 10 days of irradiation in [nuclei/primary] as a function of the beam energy for BeO

pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

A Z Isotope20 MeV - % err

No biasing20 MeV - % err 30 MeV - % err 40 MeV - % err 50 MeV - % err

182 73 Ta 1.33E-06 0.41 1.34E-06 0.36 2.86E-06 0.2108 3.79E-06 0.29 4.50E-06 0.23

181 72 Hf 6.23E-11 89.85 6.63E-05 0.13 3.21E-10 38.52 1.36E-09 23.16 4.04E-09 15.13

181 73 Ta 6.64E-05 0.14 1.02E-07 2.66 1.32E-04 0.1067 1.75E-04 0.09 2.09E-04 0.06

181 74 W 1.12E-11 99.00 1.63E-10 73.51

180 72 Hf 9.89E-08 2.82 3.40E-04 0.04 5.67E-07 1.137 1.03E-06 0.81 1.40E-06 1.05

180 73 Ta 3.40E-04 0.06 4.73E-10 18.33 6.24E-04 2.70E-002 8.05E-04 0.06 9.58E-04 0.05

180 74 W 2.84E-10 38.98 2.11E-09 24.20 2.69E-09 22.48

179 71 Lu 4.85E-10 54.37

179 72 Hf 4.99E-10 19.80 1.46E-04 0.12 6.39E-08 1.975 3.01E-07 2.03 5.65E-07 0.68

179 73 Ta 1.46E-04 0.10 2.05E-08 5.31 4.95E-04 8.65E-002 7.20E-04 0.08 8.94E-04 0.07

179 74 W 6.85E-12 99 3.44E-12 99.00 4.54E-10 21.13

178 71 Lu 2.54E-11 99 7.57E-11 61.61 2.44E-10 50.36

178 72 Hf 2.72E-09 14.43 9.01E-08 2.12 3.34E-07 0.84

178 73 Ta 2.14E-08 4.49 1.34E-09 28.24 5.73E-06 0.2028 2.01E-05 0.22 3.03E-05 0.21

178 74 W 2.04E-10 58.55

177 71 Lu 1.04E-09 19.91 2.58E-10 46.02 4.24E-09 10.95 3.37E-09 21.11 6.28E-09 9.63

177 72 Hf 3.29E-09 10.92 8.11E-08 1.52

177 73 Ta 7.05E-08 4.179 5.29E-06 0.37 1.79E-05 0.37

176 71 Lu 5.12E-10 21.03 6.05E-10 36.72 5.06E-09 13.76 1.14E-08 6.42 1.55E-08 6.61

176 72 Hf 1.97E-10 42.33 2.35E-08 5.19

Continued on next page

72

Table B.1 – continued from previous page

A Z Isotope20 MeV - % err

No biasing20 MeV - % err 30 MeV - % err 40 MeV - % err 50 MeV - % err

176 73 Ta 2.76E-08 8.17 2.03E-06 0.44

175 70 Yb 6.91E-12 99.00 2.03E-11 68.99

175 71 Lu 2.45E-09 22.15 2.40E-08 6.73 4.77E-08 4.93

175 72 Hf 6.77E-10 36.82

175 73 Ta 3.47E-08 5.14

174 70 Yb 1.12E-10 99.00

174 71 Lu 1.72E-09 20.93 1.49E-08 3.37

174 72 Hf 5.43E-11 99.00

173 70 Yb 2.81E-11 99.00

173 71 Lu 1.00E-10 99.00 4.77E-09 14.58

20 10 Ne 1.06E-09 29.30 1.87E-11 99.00 1.10E-08 7.245 2.68E-08 6.54 4.07E-08 5.06

19 9 F 4.13E-10 63.71 4.16E-10 46.84

18 8 O 8.15E-10 58.22 7.54E-10 56.18 3.00E-10 40.93

18 9 F 8.58E-11 76.45 3.51E-10 54.13

17 7 N 4.41E-10 36.38 2.53E-10 58.66 5.59E-09 13.62 1.50E-08 11.21 2.65E-08 4.58

17 8 O 1.24E-07 3.35 1.21E-07 4.17 2.88E-07 2.903 4.61E-07 2.01 6.39E-07 3.12

16 6 C 2.69E-10 39.73

16 7 N 1.87E-09 8.61 1.61E-09 12.95 3.14E-08 2.85 1.12E-07 1.60 2.12E-07 1.33

16 8 O 1.20E-07 4.06 1.23E-07 2.76 8.20E-07 0.9189 2.19E-06 0.55 3.89E-06 0.55

15 6 C 1.38E-11 99 2.50E-10 54.44 5.72E-10 35.40

15 7 N 3.04E-06 0.51 3.08E-06 0.58 5.51E-05 0.1799 1.29E-04 0.13 1.97E-04 0.07

15 8 O 9.28E-07 1.43 9.31E-07 0.90 2.06E-05 0.2569 4.89E-05 0.21 7.53E-05 0.29

14 6 C 4.37E-08 3.34 4.67E-08 2.80 1.76E-06 0.836 5.94E-06 0.56 1.03E-05 0.59

Continued on next page

73

Table B.1 – continued from previous page

A Z Isotope20 MeV - % err

No biasing20 MeV - % err 30 MeV - % err 40 MeV - % err 50 MeV - % err

14 7 N 1.15E-07 2.40 1.10E-07 2.51 8.50E-06 0.384 3.23E-05 0.19 5.86E-05 0.16

14 8 O 1.04E-09 22.57 3.90E-08 6.02 1.23E-07 1.46

13 5 B 5.51E-10 30.52 2.54E-09 14.32

13 6 C 9.91E-08 1.64 9.85E-08 1.11 1.54E-06 0.6909 8.48E-06 0.33 1.82E-05 0.27

13 7 N 9.38E-11 76.19 1.90E-10 86.02 1.99E-07 1.6 9.54E-07 0.88 1.81E-06 0.89

12 5 B 1.45E-09 28.23 1.32E-09 30.01 3.13E-08 8.633 8.54E-08 4.52 1.48E-07 2.72

12 6 C 1.58E-05 0.33 1.58E-05 0.31 7.87E-05 0.1486 1.56E-04 0.06 2.31E-04 0.08

12 7 N 1.63E-10 67.39

11 4 Be 1.28E-11 99.00

11 5 B 7.80E-07 0.68 7.98E-07 0.77 2.28E-05 0.2656 6.49E-05 0.10 1.05E-04 0.16

11 6 C 3.59E-07 1.62 3.48E-07 0.98 1.21E-05 0.2278 3.71E-05 0.14 6.24E-05 0.19

10 4 Be 2.19E-09 11.54 1.89E-09 8.15 8.96E-09 8.166 7.75E-08 2.97 3.33E-07 1.84

10 5 B 1.03E-06 0.8487 8.00E-06 0.41 1.84E-05 0.16

10 6 C 1.30E-11 99 5.37E-09 9.41 5.93E-08 5.27

9 3 Li 7.72E-10 23.66 5.36E-09 12.55 1.10E-08 7.27

9 4 Be 8.88E-08 4.89 9.14E-08 4.19 4.73E-07 1.661 2.09E-06 0.61 4.72E-06 0.52

8 3 Li 1.37E-07 2.91 1.37E-07 2.95 1.89E-06 0.3315 4.90E-06 0.46 8.11E-06 0.52

8 5 B 4.35E-10 27.34

7 3 Li 5.38E-07 1.14 5.51E-07 1.33 1.12E-05 0.296 3.87E-05 0.09 7.25E-05 0.20

7 4 Be 2.68E-08 4.68 2.78E-08 5.29 2.38E-06 0.4174 1.20E-05 0.11 2.53E-05 0.20

6 2 He 2.37E-07 0.92 2.32E-07 0.95 1.00E-06 0.7794 2.40E-06 0.58 4.21E-06 0.36

6 3 Li 1.47E-07 1.82 1.47E-07 3.14 2.65E-06 0.3395 1.30E-05 0.24 3.26E-05 0.20

4 2 He 2.18E-04 0.15 2.17E-04 0.17 9.56E-04 0.1199 1.95E-03 0.05 2.93E-03 0.05

Continued on next page

74

Table B.1 – continued from previous page

A Z Isotope20 MeV - % err

No biasing20 MeV - % err 30 MeV - % err 40 MeV - % err 50 MeV - % err

3 1 H 2.44E-07 1.35 2.40E-07 1.89 8.41E-06 0.2849 3.50E-05 0.12 7.32E-05 0.10

3 2 He 3.50E-09 16.66 3.17E-09 17.20 2.28E-06 0.7302 1.49E-05 0.22 3.44E-05 0.17

2 1 H 6.14E-07 1.20 6.17E-07 0.96 1.77E-05 0.2342 7.17E-05 0.09 1.51E-04 0.08

1 1 H 4.29E-06 0.57 4.36E-06 0.41 9.41E-05 0.1493 2.65E-04 0.06 4.54E-04 0.08

75

Table B.2 – Production rates of different isotopes after 10 days of irradiation and 5 days of cooling in [Bq] as a function of the beam energy for

BeO pellets of density ρ = 3.01 g/cm3 with a 0.8X0 converter.

A Z Isotope20 MeV - % err

No biasing20 MeV - % err 30 MeV - % err 40 MeV - % err 50 MeV - % err

182 73 Ta 1.42E+10 0.41 1.43E+10 0.36 3.05E+10 0.21 4.05E+10 0.29 4.80E+10 0.23

181 72 Hf 5.40E+05 89.85 2.78E+06 38.52 1.18E+07 23.16 3.50E+07 15.13

181 74 W 3.77E+04 99.00 5.48E+05 73.51

180 73 Ta 7.86E+08 0.06 7.86E+08 0.04 1.44E+09 0.03 1.86E+09 0.06 2.21E+09 0.05

179 71 Lu 4.08E-01 54.37

179 73 Ta 9.54E+10 0.10 9.57E+10 0.12 3.24E+11 0.09 4.72E+11 0.08 5.86E+11 0.07

178 73 Ta 2.98E+06 58.55

178 74 W 2.98E+06 58.55

177 71 Lu 2.54E+07 19.91 3.26E+07 28.24 1.03E+08 10.95 8.20E+07 21.11 1.53E+08 9.63

177 73 Ta 9.58E+08 4.18 7.19E+10 0.37 2.43E+11 0.37

176 71 Lu 1.60E-05 21.03 8.10E-06 46.02 1.59E-04 13.76 3.57E-04 6.42 4.87E-04 6.61

176 73 Ta 5.91E+04 8.17 4.34E+06 0.44

175 70 Yb 1.53E+05 99.00 4.47E+05 68.99

175 72 Hf 1.99E+08 5.30

175 73 Ta 7.85E+05 5.14

174 71 Lu 6.41E+05 20.93 5.57E+06 3.37

173 71 Lu 8.56E+04 99.00 4.07E+06 14.58

18 9 F 9.63E-14 76.45 3.94E-13 54.13

14 6 C 9.03E+03 3.34 9.66E+03 2.80 3.64E+05 0.84 1.23E+06 0.56 2.13E+06 0.59

10 4 Be 1.72E+00 11.54 1.48E+00 8.15 7.04E+00 8.17 6.08E+01 2.97 2.61E+02 1.84

Continued on next page

76

Table B.2 – continued from previous page

A Z Isotope20 MeV - % err

No biasing20 MeV - % err 30 MeV - % err 40 MeV - % err 50 MeV - % err

7 4 Be 1.91E+08 4.68 1.98E+08 5.29 1.70E+10 0.42 8.54E+10 0.11 1.80E+11 0.20

3 1 H 2.34E+07 1.35 2.30E+07 1.89 8.07E+08 0.28 3.36E+09 0.12 7.02E+09 0.10

77

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