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Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science and Technology, Sichuan University, China Research Coordination Meeting, IAEA, Vienna, 4-6 Mar ch 2009
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Page 1: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

Electron-impact inner shell ionization cross section measurements for heavy element

impurities in fusion reactors

Jingjun Zhu

Institute of Nuclear Science and Technology,Sichuan University, China

Research Coordination Meeting, IAEA, Vienna, 4-6 March 2009

Page 2: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

Contents

  1. Introduction

  2. Our experimental method

  3. Experiment results

  4. Summary

Page 3: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

main experimental methods :

• to measure the characteristic x-rays • to measure the Auger electrons targets : self-supporting thin targets ( △ E/E~0.01 )

Experimental sketch :

1 Introduction

Page 4: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

d

ratiointensity ray - xK toK,/ electronsincident ofNumber ,

electrons of angleIncident , target of thicknessmesDensity ti,

weighttomicconstant/A Avogadro,/ ray -X ofnumber Counting ,

angle solid timesEfficiency, section cross ionization shell-K ,

1cos4

IIN

d

ANEN

EQ

I

I

dNN

AENEQ

e

Ax

k

keA

xk

Si(Li) detector

X-ray

e

Thin target

Page 5: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

Problems of the self-supporting thin targets:

1) preparing the self-supporting thin targets, is the main difficulty:

20 keV electrons d= Fe: 300Å Cu: 276Å Mo: 270Å W: 179Å Pb: 166Å 30 keV electrons d= Fe: 602Å Cu: 553Å Mo: 537Å W: 351Å Pb: 330Å

2) not easy to making use of it

Page 6: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

2. Our experimental method

Application of vacuum coating technique to prepare thi

n

target on thick film. Advantage: easy to prepare the

targets.

Detecting the characteristic x-rays by a Si(Li) detector.

However, ionization contribution in thin target by

electrons reflected from the substrate must be corrected.

Page 7: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

d

Si (Li) detector

Thin target

Thick substrate

Experimental sketch :

Page 8: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

),,0(),0(

surface substrateat

energy on fluence aldifferenti theis ),,0(

and substrates from

electrons reflected of spectrumenergy theis ),0( :Definition

)(),0(cos1cos4

4

EdE

E

E

EdEQEI

I

dNN

AENEQ

refref

ref

ref

E

E

krefkeA

xk

k

Bipartition model

Page 9: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

a. Calculation of electron reflection energy spectrum : —Bipartition model

Electron reflection energy spectra calculated by the bipartition model for 20 keV electrons from Mylar ( solid line ) and Al ( dashed line ) su

bstrates. The incident angle is 45 degrees.

Page 10: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

b. Correction for multiple scattering

• by Monte Carlo method

d’/d: ratios of electron mean track length to straight target thickness

Page 11: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

c. Thickness measurements of thin targets

• By Rutherford Backscattering Spectrometry ( RBS) ( The accuracy can be about 5% )

Page 12: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

RBS experimental spectrum of thin Ti target on thick Al substrate and the simulation curve using GISA3.3 code. The 2 MeV 4He+ ions were impacted vertically on the target. The backscattered particles were detected at a scattering angle of 1500 by a Si surface-barrier detector.

RBS example:

Al

Page 13: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

d. Efficiency calibration of Si(Li) detector:

the shape of the efficiency calibration curve was determined from the ratio of experimental and theoretical thick carbon target (PENELOPE code) bremsstrahlung spectra produced by incident electrons. the absolute value for the efficiency calibration was obtained from the use of 241

Am radioactive standard source.

Page 14: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

Experimental set-up for RBS

Page 15: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

Experimental set-up for ionization cross-sections

Page 16: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

3.Experiment results

3.1 Thin target method

By using the method for thin targets on a thick substrate, we have measured the electron-impact inner-shell ionization cross sections near the threshold energies for the following elements and shells:

S-K, Cl-K, Ca-K, Zn-K,

W-L,L, Bi-L,L, Ba-L and Gd-L.

Page 17: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of K-shell ionization cross sections by electron impact for S element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger.

S-K

Page 18: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of K-shell ionization cross sections by electron impact for Cl element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger.

Cl-K

0 5 10 15 20 25 30 35

0.0

1.0x10-21

2.0x10-21

3.0x10-21

4.0x10-21

5.0x10-21

Cl K shell This work PWBA-Ex-C Luo and Joy Casnati Hombourger

Cro

ss s

ectio

n (c

m2 )

E(keV)

Page 19: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of K-shell ionization cross sections by electron impact for Ca element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger. The experimental data of Shevelko and co-workers for Ca element are also plotted for comparison.

Ca-K

Page 20: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of K-shell ionization cross sections by electron impact for Zn element are compared with the results from the PWBA-C-Ex theory and the Luo and Joy’s theory as well as the results from the empirical formulae of Casnati and co-workers and of Hombourger and of Gryzinski. The experimental data of Tang and co-workers for Zn element are also plotted for comparison.

Zn-K

Page 21: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of Lα, Lβ x-ray production cross sections by electron impact for W element are compared with the PWBA-C-Ex theory and the experimental data of Campos et al.

W-Lα,Lβ

Page 22: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of Lα, Lβ x-ray production cross sections by electron impact for Bi element are compared with the PWBA-C-Ex theory.

Bi-Lα,Lβ

Page 23: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of Lα x-ray production cross sections by electron impact for Ba element are compared with the PWBA-C-Ex theory.

Ba-Lα

Page 24: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The present experimental data of Lα x-ray production cross sections by electron impact for Gd element are compared with the PWBA-C-Ex theory.

Gd-Lα

Page 25: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

3.2 Thick target method

By using the thick-target method, we measured the K-shell ionization cross sections near the threshold energies for Ni and Si element.

( Physical Review A 77, 2008, 042702 )

Page 26: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The measured K-shell ionization cross sections for Si element by the thick-target method. The predictions of DWBA and PWBA-C-Ex theories and the values of Casnati empirical formula [18] are also shown for comparison.

Si-K

Page 27: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

The K-shell ionization cross sections for Ni element determined by the Tikhonov regularization method (circles, in red) and the classical molecular dynamics (CMD) method (triangles, in blue) for the real experimental data. The experimental data of Llovet et al (squares, in black) and the predictions of DWBA (dashed line) and PWBA-C-Ex (solid line) theories are also shown for comparison.

Ni-K

Page 28: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

3.3 Effect of surface roughnessStudied using Monte Carlo simulations.

The effect of surface roughness increases as the roughness increases.

The surface roughness of the target should be limited to less than 100 nm if the experimental error originated from the surface roughness would be kept less than 2%.

( NIM B 266(23), 2008, 5037-5040 )

Page 29: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

4. Summary:

By using the method for thin targets on a thick substrate, we have measured the electron-impact inner-shell ionization cross sections near the threshold energies for the following elements and shells: S-K, Cl-K, Ca-K, Zn-K, W-L,L, Bi-L,L, Ba-L and Gd-L.

By using the thick-target method, we measured the K-shell ionization cross sections near the threshold energies for Ni and Si element.

The effect of surface roughness increases as the roughness increases and the surface roughness of the target should be limited to less than 100 nm if the experimental error originated from the surface roughness would be kept less than 2%.

Page 30: Electron-impact inner shell ionization cross section measurements for heavy element impurities in fusion reactors Jingjun Zhu Institute of Nuclear Science.

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