69th NUPECC meeting October 8, 2010

1

Electron transferElectron transfer into into metastable metastable HeHe-like ions: -like ions:

Investigation of Investigation of non-statistical non-statistical population mechanisms population mechanisms

Theo J.M. ZourosTheo J.M. ZourosDept. of Physics, University of Crete Dept. of Physics, University of Crete

Heraklion, Crete, GREECEHeraklion, Crete, GREECE

A proposal for A proposal for atomic collisionatomic collision experiments experiments at the Demokritos TANDEMat the Demokritos TANDEM

3-electron spectrum 3-electron spectrum from collisions of He-like beamfrom collisions of He-like beam

1.1 MeV/u1.1 MeV/u

F F 7+7+ (1s (1s22) 75%) 75%

F F 7+7+ (1s2s (1s2s 11S) <1%S) <1%F F 7+7+ (1s2s (1s2s 33S) 24%S) 24% ττ1/21/2 = = 277 277 μμss

ττ1/21/2 = 0.198 = 0.198 μμss

ττ1/21/2 = = stablestable

3-electron spectrum 3-electron spectrum from collisions of He-like beamfrom collisions of He-like beam

1.1 MeV/u1.1 MeV/u

F F 7+7+ (1s (1s22) 75%) 75%

F F 7+7+ (1s2s (1s2s 11S) <1%S) <1%F F 7+7+ (1s2s (1s2s 33S) 24%S) 24% ττ1/21/2 = = 277 277 μμss

ττ1/21/2 = 0.198 = 0.198 μμss

ττ1/21/2 = = stablestable

Spin statistics for 2p capture to Spin statistics for 2p capture to purepure 1s2s 1s2s 33S S

Sss 321

HeHe-like-likeInitial StatesInitial States

+ 2p+ 2p

Sss 121

Ss 121

<1 %<1 %

6

4

6

2

ProbabilityProbability

PpSss 23 2)21(

Spin statistics for 2p capture to 1s2s Spin statistics for 2p capture to 1s2s 33S S

PpSss 43 2)21(

Sss 321

HeHe-like-likeInitial StatesInitial States

+ 2p+ 2p

Sss 121

1s1s22

6

4

6

2

ProbabilityProbability

PpSss 23 2)21(

Spin statistics for 2p capture to 1s2s Spin statistics for 2p capture to 1s2s 33S S

PpSss 43 2)21(

LiLi-like-likeFinal StatesFinal States

Sss 321

HeHe-like-likeInitial StatesInitial States

+ 2p+ 2p

Sss 121

1s1s22

Ppss 4221

PPpss 23 )22(14

1

6

4

6

2

ProbabilityProbability

PpSss 23 2)21(

Spin statistics for 2p capture to 1s2s Spin statistics for 2p capture to 1s2s 33S S

PpSss 43 2)21(

LiLi-like-likeFinal StatesFinal States

PPpss 21 )22(14

3

Spin recouplingSpin recouplingSss 321

HeHe-like-likeInitial StatesInitial States

+ 2p+ 2p

Sss 121

1s1s22

Ppss 4221

44P : P : 22PP__ : : 22PP++

12

3

12

1

12

8Final Final

breakdownbreakdown 2:12:1

Obtaining Obtaining purepure metastable beam contributions metastable beam contributions

Strohschein et al PRA 2008Strohschein et al PRA 2008

Obtaining Obtaining purepure metastable beam contributions metastable beam contributions

Strohschein et al PRA 2008Strohschein et al PRA 2008

Pure metastablePure metastable = Mixed - Ground= Mixed - Ground

Obtaining pure metastable beam contributionsObtaining pure metastable beam contributions

Strohschein et al PRA 2008Strohschein et al PRA 2008

Spin statisticsSpin statistics

So why the bigSo why the bigdiscrepancy???discrepancy???

Pauli exchange interactionPauli exchange interaction

• An electron with An electron with antialignedantialigned spin spin can populate either the 1s, 2s or can populate either the 1s, 2s or 2p2p levels, in the later case giving levels, in the later case giving rise to the rise to the 22PP++ state state

Pauli exchange interactionPauli exchange interaction

• An electron with a spin An electron with a spin alignedaligned with the spin of the 1s projectile:with the spin of the 1s projectile: a) can be captured into the a) can be captured into the 2p2p directly to form the directly to form the 44PP state state

b) b) cannotcannot be captured into the 1s be captured into the 1s (or 2s) due to (or 2s) due to Pauli exclusion. Pauli exclusion. So instead it interacts with the 1sSo instead it interacts with the 1s (or 2s) via a(or 2s) via a Pauli Exchange InteractionPauli Exchange Interaction so that one of them is transferred toso that one of them is transferred to the the 2p2p forming additional forming additional 44PP states states

Tanis et al Tanis et al PRL2004PRL2004

Tanis et al considered capture only to n=2

Significant capture to higher n=3-7 indicated by our CDW calculations

Overlooked channel:Radiative cascade Feeding!

nl

OrderOrderCascade feeding 1s2s2p Cascade feeding 1s2s2p 44P analysisP analysis

Quartet Quartet Doublet Doublet NOTNOT allowed!allowed!

Quartet Quartet Quartet Quartet allowed!allowed!

Strong cascade feeding Strong cascade feeding of 1s2s2p of 1s2s2p 44PP

OrderOrder

Zouros et al, Zouros et al, Phys. Rev. A Rapid Comm. 2008Phys. Rev. A Rapid Comm. 2008

Cascade feeding 1s2s2p Cascade feeding 1s2s2p 44P analysisP analysis

OrderOrderCascade feeding 1s2s2p Cascade feeding 1s2s2p 22P analysisP analysis

All transitions All transitions allowed!allowed!

However However AugerAuger transitions transitions much stronger!much stronger!

They They rapidly depleterapidly deplete higher lying levels!higher lying levels!

NO effective NO effective cascade feeding!cascade feeding!

OrderOrder

Zouros et al, Zouros et al, Phys. Rev. A Rapid Comm. 2008Phys. Rev. A Rapid Comm. 2008

Cascade feeding 1s2s2p Cascade feeding 1s2s2p 22P analysisP analysis

Cascade feeding Cascade feeding accounts accounts

for about 50% for about 50% of the observed of the observed enhancementenhancement

Final verdictFinal verdict

So what is the rest due to?So what is the rest due to?

Proposal• Isoelectronic sequence study using He-like ions from

Li+ to F7+ in the 0.1-0.5 MeV/u where capture is strongest and effect seems to be the largest

Proposal• Isoelectronic sequence study using He-like ions from

Li+ to F7+ in the 0.1-0.5 MeV/u where capture is strongest and effect seems to be the largest

• Ideally suited to the Demokritos tandem energy range of 0.8-4 MV.

Proposal• Isoelectronic sequence study using He-like ions from

Li+ to F7+ in the 0.1-0.5 MeV/u where capture is strongest and effect seems to be the largest.

• Ideally suited to the Demokritos tandem energy range of 0.8-4 MV

• Needed: terminal gas stripper to produce pure ground state He-like beams – low intensity beams ~1-10nA

Proposal• Isoelectronic sequence study using He-like ions from

Li+ to F7+ in the 0.1-0.5 MeV/u where capture is strongest and effect seems to be the largest.

• Ideally suited to the Demokritos tandem energy range of 0.8-4 MV

• Needed: terminal gas stripper to produce pure ground state He-like beams – low intensity beams ~1-10nA

• Will use electron hemispherical spectrometer with position sensitive detector for high quality statistics ideally suited for working with low intensity beams

Proposal• Isoelectronic sequence study using He-like ions from

Li+ to F7+ in the 0.1-0.5 MeV/u where capture is strongest and effect seems to be the largest

• Ideally suited to the Demokritos tandem energy range of 0.8-4 MV

• Needed: terminal gas stripper to produce pure ground state He-like beams – low intensity beams ~1-10nA.

• Will use electron hemispherical spectrometer with position sensitive detector for high quality statistics ideally suited for working with low intensity beams

• Spectrometer and collision chamber already in house however need to be connected to a new beam line

1/11/2007

New ZAPS setup: Single stage 00 HDA with injection lens and 2-D position sensitive detector

5104.14

%,20%,1.0

acceptE

E

E

E

Gas in Pressure Gauge

Gas Cell

PSDX-PositionY- Position

Timing

4-element lens

Faraday Cup

Inner hemisphere

electrons

Outerhemisphere

F7+

Target gas nt ~1012 #/cm3Differential

Pumpingports

Focusing and retardation

Chamber pressure~10-7 Torr

Overall efficiency gain ~ 20-50High Transmission ~ 90%

Paracentric entry

The end – thank you for listeningThe end – thank you for listening

ContactContact: tzouros@physics.uoc.gr: tzouros@physics.uoc.gr

Non-statisticalNon-statistical results results• Tanis et al.Tanis et al. PRL 92 (2004) 133201 PRL 92 (2004) 133201• Zouros et al.Zouros et al. PRA 77 (2008) 050701 PRA 77 (2008) 050701• Strohschein et al.Strohschein et al. PRA 77 (2008) 022706 PRA 77 (2008) 022706• Rohrbein et alRohrbein et al, PRA 81 (2010) 042701, PRA 81 (2010) 042701

Production of Production of purepure ground state He-likeground state He-like ion beams ion beams• Benis & ZourosBenis & Zouros, , PRA 65 (2002) 064701PRA 65 (2002) 064701

ReferencesReferences

Yield correctionsYield corrections due to due to 44PPJJ metastability metastability

1.1 MeV/u1.1 MeV/u

ImportantImportantYield correctionYield correction

Yield correctionsYield corrections due to due to 44PPJJ metastability metastability

ImportantImportantYield correctionYield correction

1.1 MeV/u1.1 MeV/u

Yield correctionsYield corrections due to due to 44PPJJ metastability metastability

1.1 MeV/u1.1 MeV/u

ImportantImportantYield correctionYield correction

1.1 MeV/u1.1 MeV/u