Download - Radioactive Ion Beam (RIB) Production at ISOLDE by the Laser Ion Source and Trap (LIST) Sven Richter for the LIST-, RILIS- and ISOLDE IS456 Collaborations.

Radioactive Ion Beam (RIB) Production at ISOLDEby the Laser Ion Source and Trap (LIST)

Sven Richter for the LIST-, RILIS- and ISOLDE IS456 Collaborations

222nd of February 2013 | LA³NET Laser Based Particle Sources 2013 | Sven Richter | [email protected]

Content

− Upgrade of the ISOLDE RILIS towardsfull suppression of isobaric contaminations

− Standard operation of the ISOLDE RILIS− Principle of the Laser Ion Source and Trap

− LIST offline & LIST online run 2011− LIST online run 2012

• Motivation:

• Experimental Setup:

• Results:

• Summary


Motivation: Reduction of Isobaric Contamination

Protons1,4 GeV

NuclearReactionTarget

Hot cavity atomizer Laser beamsMass-marker

Extraction

• Nickel-78 ion beam: Example of isobaric contamination

• Cross-section production of different isotopes in a UCx target with 1.4 GeV protons


Scheme of RILIS at ISOLDE

Slide: D. Fink

Panoramic view of the RILIS laser setup:

Very efficient and element selective ionization!

Element unique RILIS schemes Principle of RILIS

E0

E1

E2

Rydbergstate

AIS

IP

Atom

Ion

RILI

S la

sers


Dual RILIS Laser Setup

RILIS Dye Laser System GPS/HRS

Target & Ion Source

RILIS Ti:Sa Laser System

pA – meter

Faraday cup…

SHG/THG/FHG

l – meter

Ti:Sa 2

l – meterDye 2 SHG

Narrowband Dye

THGDye 1

Ti:Sa 1

Ti:Sa 3

Nd:YAG

Nd:YAG

10 kHz Master clock

Delay generator

LabVIEW based DAQSlide: S. Rothe


Ion Source & Beam Purity

• Nonselective surface inonization in hot cavity

• Strong interference in experiments by isobaric contamination

Surface Ionization


Ion Source & Beam Purity

• Increase of ionization efficiency for the element of interest

• Better selectivity but no suppression of isobaric contaminants

RILIS


• Suppression of surface ions by electrostatic repeller• High selective laser ionization inside the LIST• Ion guide towards extraction by transverse rf-trapping field

Ion Source & Beam PurityLaser Ion Source & Trap

Na23

Mg24

Al27Mg25 Mg26

ion

curr

ent [

A]

mass [u]


Principle of using the LIST at ISOLDE

Slide: D. Fink

RILIS cabin High voltage cage

Target areaISOLDE hall

Nd:YAG Dye 1

1. 285 nm (UV)

3. 532 nm

SHG

60 keV

2. 552 nm

Repeller voltage

Rf-generator

+

++

Detectors: tape station, Faraday cup, MCP, WINDMILL

Separator magnet

Remote control

GPS

+

+

20m

Glass fiber

Dye 2

Mg RILIS setup


LIST run in 2011: results

• First on-line test of the LIST in May 2011Physics case: Mg

• Realistic on-line conditions over 48 hours

• Suppression limited by backgroundof Faraday cup

• No significant changes of LIST performance during online run

50LIST

RILIS

IC

IC6001

LIST

RILIS

IC

IC

-200 -100 0 100 2001E-12

1E-11

1E-10

39K before p 39K after p

Ion

Curre

nt (A

)Repeller Voltage (V)

Effective suppression of surface ions but with lower laser ionization efficiency.


LIST run in 2012: overview

RILIS schemes for Po

UCx target

Annular Si Si216Pobeam

C-foils20 mg/cm2

α detector (Windmill, Leuven)

Goals of 2nd LIST online run:

• First real online application of LIST at ISOLDE

• Provide highly purified beams of Mg and Po

• Proof of principle with strongly outgassing UCx target

• Test of improved LIST design for higher efficiency


LIST run in 2012: suppression

RILIS vs. LIST mode

(2011) 27Mg:

30Mg:

208Po:20

LIST

RILIS

IC

IC

50LIST

RILIS

IC

IC

(2012)

Analysis of suppression factors for different isotopes

Suppression

• Usually > 3 orders of magnitude

• Exceptions observed for some isotopes

Limits by LIST electrode structure

Supp

ress

ion

fact

or


LIST run in 2012: suppression limits

Suppression Limits

• Deposit of neutral atoms on quadrupole rods

• Decay inside the LIST

• Other ionization mechanisms

Secondary isobaric contamination


Unexpected production of short-lived isotopes

217Rn: T1/2 = 540µs,α-decay of 221Ra

α-spectrum at mass 217u:

217 R

n

α-spectrum at mass 216u:

216At: T1/2 = 300µs,α-decay of 220Fr

• Deposit of mother nuclei (e.g. 220Fr, 221Ra) on quadrupole rods

• Decay inside the LIST

• Other ionization mechanisms and extraction towards ISOLDE beam line

0.2 counts/sec of short-lived isotopes (216At, 217Rn)

general half life of produced isotopes at ISOLDE: > 1 ms


LIST run in 2012: Laser Spectroscopy on Po

Two measurement campaigns in 2007 and 2009 at ISOLDE/CERN

• Several Po-isotopes remained unstudied due to strong Fr-contamination

• Using LIST to suppress Fr contamination in 2012

Mean square radii of Po-isotopes among other elements:

Work of T. E. Cocolios, M. Seliverstov et al.


Polonium Spectroscopy: HFS and IS• New Po-decay data on mass 219

Direct measurement of IS of 216Po and 217Po

Prelim

inary

• 216Po and 217Po in one measurement

Laser frequency offset, GHz

Slide: D. Fink


Summary

• Suppression of isobaric contamination and selectivity improvement of RILIS by LIST

• Proof of principle by 2011 on-line run:

o Suppression of > 1000

o Ionization efficiency reduction of ≈50 (Mg)

• First real physics application in 2012:

o Laser spectroscopy of 216-217Po possible due to suppression of Fr by LIST

o Suppression factor > 1000

(limited by depositon and decay inside the LIST for few isotopes)

o Ionization efficiency reduction of ≈20 (Mg,Po)

o Production of ion beams of short-lived ions by in-trap decay

LIST demonstrated its ability – a new option for ISOLDE users


Thank you for LISTening

… and special thanks to all the collaborators:


Outlook

• Analyzing rf-field of the LIST by simulations

• Almost the same rf-field in centeras with large rod diameter

• 5 times higher rf-voltage necessary

• next step: planning a prototype

• Improvements for the next LIST version

• Ensuring suppression for all isotopes

• Avoid deposit of neutral atoms on quadrupole structure

Surface reduction of quadrupole rods


LIST Parameters

• Two operational modes of LIST:− RILIS (ion guide) mode− LIST (repelling) mode

• Electrode potential (Repeller):− -50 V (ion guide)− 10 V (repelling)

• LIST RF field ( 1 MHz)− Amplitude 10 – 1000 Vpp

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