high resolution auger projectile electron spectroscopy of li-like ions produced by electron capture...

HIGH RESOLUTION AUGER PROJECTILE ELECTRON SPECTROSCOPY OF LI-LIKE IONS

PRODUCED BY ELECTRON CAPTURE OF HE-LIKE IONS

IN COLLISIONS WITH GASEOUS TARGETS

CDAMOP Delhi Mar 12, 2015

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

Heraklion, Crete, GREECEAtomic Collisions & Electron Spectrometry Laboratory

&Institute of Nuclear and Particle Physics, Demokritos, Athens

Focus on


Non-statistical production of 1s2s2p 4P and 1s2s2p 2P states by

e- capture to the 1s2s 3S state:A persisting puzzle!

Accelerator-based atomic physics topic(ion-atom collisions)

1s2s2p 3-electron spectrum resulting

from e- capture to He-like beame- Analyzer

F6+ (1s2s 3S2p) ion


2P±

4P1480 1500 1520 1540

0

2

4

6

8

10

12

14

12 MeV C4+ W=1521eV, F=4 (VL4=-684.45V,VL5=1399.32V)

1s2

p2 2 D

1s(2

s2

p1 P)2 P

+

1s(2

s2

p

3 P)2 P

-

1s2s2p 4P

1s2

s2 2 S

Ne (20mTorr)

No

rma

lize

d e

lectr

on

Yie

lds (

x 1

0-1

1 )

Laboratory Energy (eV)

R = 4P/(2P+ + 2P-)

C4+ (1s2) 75%

C4+ (1s2s 3S) 20% τ1/2 = 20.6 ms

τ1/2 = ∞ - stable

e- Analyzer


1s2s2p 3-electron spectrum resulting from e- capture to He-like beam

F6+ (1s2s 3S2p) ion

2P±

4P

Interest in ratio4P/2P

1480 1500 1520 15400

2

4

6

8

10

12

14

12 MeV C4+ W=1521eV, F=4 (VL4=-684.45V,VL5=1399.32V)

1s2

p2 2 D

1s(2

s2

p1 P)2 P

+

1s(2

s2

p

3 P)2 P

-

1s2s2p 4P

1s2

s2 2 S

Ne (20mTorr)

No

rma

lize

d e

lectr

on

Yie

lds (

x 1

0-1

1 )


R = 4P/(2P+ + 2P-)

He-like beam components:

C4+ (1s2s 1S) 5% τ1/2 = 3 μs

Obtaining pure ground state beam contributions

Foilstripping

Gas stripping


Mixed state (1s2, 1s2s 3S) Spectrum

25% metastable

Theory

Obtaining pure ground state beam contributions

Benis et al PRA 2004

Foilstripping

Gas stripping

Gas stripping at lower energiesProduces He-like ions mostly in ground state!


Mixed state (1s2, 1s2s 3S) Spectrum

25% metastable

TheoryPractically pure ground state (1s2)

Spectrum< 3% metastable


Ratio 4P/2P

1480 1500 1520 15400

2

4

6

8

10

12

14

12 MeV C4+ W=1521eV, F=4 (VL4=-684.45V,VL5=1399.32V)

2D

2P+

2P-

4P

2S

Ne (20mTorr)

Nor

mal

ized

ele

ctro

n Y

ield

s (x

10

-11)


R = 4P/(2P+ + 2P-)

• Independent of most instrumental parameters (i.e. detector efficiency, number of ions, target pressure, etc.)

• Obey spin statistics• Unexpected value could reveal existence of underlying processes

Spin statistics for 2p capture to pure 1s2s 3S

Sss 321

He-likeInitial States

+ 2p

Sss 121

Ss 121


6

4

6

2

Probability

PpSss 23 2)21(

Spin statistics for 2p capture to 1s2s 3S

PpSss 43 2)21(

Sss 321


+ 2p

Sss 121

1s2


1480 1500 1520 15400

2

4

6

8

10

12

14

12 MeV C4+ W=1521eV, F=4 (VL4=-684.45V,VL5=1399.32V)

2D

2P+

2P-

4P

2S

Ne (20mTorr)

Norm

alized e

lectr

on Y

ield

s (

x 1

0-1

1 )


R = 4P/(2P+ + 2P-)

6

4

6

2

Probability

PpSss 23 2)21(


PpSss 43 2)21(

Li-likeFinal States

Sss 321


+ 2p

Sss 121

1s2

Ppss 4221

1480 1500 1520 15400

2

4

6

8

10

12

14

12 MeV C4+ W=1521eV, F=4 (VL4=-684.45V,VL5=1399.32V)

2D

2P+

2P-

4P

2S

Ne (20mTorr)

Norm

alized e

lectr

on Y

ield

s (

x 1

0-1

1 )


R = 4P/(2P+ + 2P-)

PPpss 23 )22(14

1

6

4

6

2

Probability

PpSss 23 2)21(


PpSss 43 2)21(

Li-likeFinal States

PPpss 21 )22(14

3

Spin recouplingSss 321


+ 2p

Sss 121

1s2

Ppss 4221

4P : 2P- : 2P+

12

3

12

1

12

8

Final breakdown 2:1


Ratio 4P/2P

1480 1500 1520 15400

2

4

6

8

10

12

14

12 MeV C4+ W=1521eV, F=4 (VL4=-684.45V,VL5=1399.32V)

2D

2P+

2P-

4P

2S

Ne (20mTorr)

Nor

mal

ized

ele

ctro

n Y

ield

s (x

10

-11)


R = 4P/(2P+ + 2P-)

Expected ratio from spin statisticsAfter subtraction ofGround state “contamination”

4P/2P = 2

Obtaining pure metastable beam contributions

Strohschein et al PRA 2008 CDAMOP Delhi Mar 12, 2015

Obtaining pure metastable beam contributionsPure metastable stateMixed – Norm. Ground state =

In 2008Tanis and companyUsed this technique

to measure both mixed and ground

state contributions in C 4+ beams

The spectra were then normalized and subtracted leaving

the pure metastable component only!


Existence of 2D line

evidence of incomplete subtraction

Strohschein et al PRA 2008 (WMU - Kalamazoo)

Obtaining pure metastable beam contributions

Strohschein et al PRA 2008

Spin statistics

Pure metastable state


So why the bigdiscrepancy!?

Ratio of 4P/2P

First explanation: Pauli exchange interaction?

• An electron with antialigned spin can populate either the 1s, 2s or 2p levels, in the later case giving rise to the 2P+ state

• Cannot form 1s2s2p 4P


WMU

1s2s 3S

Pauli exchange interaction

• A target electron with spin aligned to the spin of the 1s projectile:

a) can be captured into the 2p directly to form the 1s2s2p 4P

b) CANNOT be captured into the 1s (or 2s) due to Pauli exclusion.

Tanis et al PRL2004

The Pauli Exchange Interaction is reminiscent of the Transfer-Excitation mechanism, but with two identical electrons doing the Transfer and the Excitation! - Rather puzzling and difficult to calculate (not possible to date!)

New idea: So instead it interacts with the 1s (or 2s) e- via a Pauli Exchange Interaction with one e- transferred to the 2p forming additional 4P states


Weird?!

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

Alternative hypothesis: Cascade feeding

OrderCascade feeding 1s2s2p 4P analysis

Quartet Doublet NOT allowed!

Quartet Quartet allowed!

Strong cascade feeding of 1s2s2p 4P !

For a state p:

transitionsdepopulating populating

E1Selection Rules:


Cool!

Slow A

uger

Order

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

Cascade feeding 1s2s2p 4P analysis


Slow A

uger


But wait a minute!

Shouldn’t the cascades also feed the 2P states tooThus also enhancing the denominator

of the 4P/2P ratio?

Indeed! But …

OrderCascade feeding 1s2s2p 2P analysis

Same E1 selection rules!However now

Auger transitions to ground state much stronger!

They rapidly deplete higher lying levels!

Minimal cascade feeding

of 1s2s2p 2P ! CDAMOP Delhi Mar 12, 2015

Fast

Aug

er

Order

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

Cascade feeding 1s2s2p 2P analysis


Fast

Aug

er

This selective Cascade feeding

mechanism accounts

for about 50% of the observed enhancement

Similar results also presented for C4+

So what is the rest due to?Strohschein et al PRA 2008

70%

Röhrbein, Kirchner, Fritzsche PRA 2010

EXCELLENT QUESTION!


In progress:• Installation of terminal gas stripper to

produce ground state beams• Installation of post strippers (foil and gas)

to produce He-like ions at lower energies

Investigation of the systematics of the 4P/2P ratio in an Isoelectronic sequence study using He-like ions from Li+ , B3+ , C4+ , N5+ , O6+ , F7+ in the 0.1-2 MeV/u

Use different targets such as H2, He, Ne, Ar Ideally suited to the Demokritos tandem

accelerator energy range of 0.8-5 MV.

2013 - APAPES Proposal granted!

New results 2014-2015

APAPES Strohschein 2008


Comparison

0

50

100

150

12 MeV C4+

2D

2P+

2P-

4P

2S

Mixed (1s2 + 1s2s 3S) Gaussian fits

C4+ + Ne

12 MeV C4+

220 225 230 235 240 245 2500

2

4

6

8

10

12

No

rma

lize

d Y

ield

s (

arb

.un

its)

Electron Energy (eV)

C4+ + He

Similar energy resolution

New results 2014-2015APAPES

Our new results look very similar – except for 2-3 times larger and wider 4P!???

Comparison

0

50

100

150

200

250

12 MeV C4+

2D

2P+

2P-

4P

2S

Mixed (1s2 + 1s2s 3S) Gaussian fits

C4+ + Ne

12 MeV C4+

220 225 230 235 240 245 2500

5

10

15

20

No

rma

lize

d Y

ield

s (

arb

.un

its)

Electron Energy (eV)

C4+ + He

Strohschein 2008

0.25 0.50 0.75 1.00 1.25 1.50 1.750

3

6

9

spin statistics

C4+ + He WMU (4P/2P)

APAPES (4P/2P)

Incident C4+ Energy (MeV/u)

0

3

6

9 WMU (4P/2P)

APAPES (4P/2P)

4 P/2 P

C4+ + Ne

spin statistics


Ratio comparison

NewResults

Give muchLower 4P/2PRatio!

But much closer

To 2!

(after correction for solid angle effect in 4P due to its long life time)


Consistency Check ratio

2P+/2P-

Preliminary! However

2P+/2P-Ratio seems

Good For all!

0.25 0.50 0.75 1.00 1.25 1.50 1.750

3

6

9

spin statistics

spin statistics

C4+ + He WMU (4P/2P)

APAPES (4P/2P)

WMU (2P+/2P-)

APAPES (2P+/2P-)

Incident C4+ Energy (MeV/u)

0

3

6

9

spin statistics

spin statistics

2P+

/ 2P-

WMU (4P/2P)

APAPES (4P/2P)

WMU (2P+/2P-)

APAPES (2P+/2P-)

4 P/2 P

C4+ + Ne


0

2

4

6

Norm.yields Norm.fit

Ne

12 MeV C4+ W=1521eV,F=4, VL4 =-684.45V,VL5=1399.32V

0

2

4

He4P

2P-2P+ 2D

0

2

4

Nor

mal

ized

ele

ctro

n Y

ield

s (x

10-1

1)

(arb

.uni

ts)

H2

2S

220 225 230 235 240 245 2500

2

4

Auger electron Energy (eV)

ArNew calculations are needed

to evaluate capture and cascade contributions for all measured

collision systems

More New results 2014-2015

0

1

2

3

4

5

6

2P-

Ne (20 mTorr) Fit

18 MeV C4+ W=1966eV, F=4

2P+

Nor

mal

ized

ele

ctro

n Y

ield

s (

10-1

1 )

2S

4P

2D

0

1

2

3

Ne (20 mTorr) Fit

2S

4P

2P-2P+

2D

220 225 230 235 240 245 250

0

1

2

3

4

5

6

2P-

Ar (5 mTorr) Fit

2S

4P

2P+

2D

220 225 230 235 240 245 250

0

1

2

3

2P-

Ar (5 mTorr) Fit

12 MeV C4+ W=1521eV, F=4

Auger Electron Energy (eV)

2S

4P

2P+

2D

New targets Higher Energy – 18 MeV

Zero-degree Auger Projectile spectroscopy setups:1s2s2p 4P yield correction for long-life times


WMUAPAPES -12 MeV C4+

10-4

10-3

10-2

10-1

100

101

10-5

10-4

10-3

10-2

10-1

0 50 100 150 200 250 300

10-7

10-6

10-5

10-4

10-3

10-2

0(s

0-z

) (

sr)

= m

ax

J=1/2 =3.7 ns J=3/2 =13.2 ns J=5/2 =117.2 ns

Tem

pora

l Ter

m F

T (

mm

-1)

0(s

0-z

) F

T(z

) (s

r/m

m)

Z (mm)

28.9cm

1.1 MeV/u

F7+

τ1/2 = 0.735 ns

τ3/2 = 7.88 ns

τ5/2 = 16.3 ns

5.8cm

ImportantYield correction

Factor (x 2.5)

1.1 MeV/u

For C4+ 4P correction factors:

7.3, 8.8, 10.2 for 6, 9, 12 MeVStrohschein PRA 2008

1s2s2p 4P metastable solid angle correction factor – WMU – two-stage parallel plate Analyser (2PPA)


1.1 MeV/u

F7+

τ1/2 = 0.735 ns

τ3/2 = 7.88 ns

τ5/2 = 16.3 ns

5.8cm

10-4

10-3

10-2

10-1

100

101

10-5

10-4

10-3

10-2

10-1

0 50 100 150 200 250 300

10-7

10-6

10-5

10-4

10-3

10-2

0(s

0-z

) (

sr)

= m

ax

J=1/2 =3.7 ns J=3/2 =13.2 ns J=5/2 =117.2 ns

Tem

pora

l Ter

m F

T (

mm

-1)

0(s

0-z

) F

T(z

) (s

r/m

m)

Z (mm)


APAPES

Calculated by SIMION Monte Carlo

12 MeV C4+

1s2s2p 4P metastable solid angle correction factor – APAPES Hemispherical Deflector Analyzer (HDA)

28.9cm

Summary and Conclusion


• More measurements still needed for different collision systems to better check systematics (APAPES) • Follow up cascade calculations• Tests of solid angle correction factors to 4P• Can someone please calculate the Pauli Exchange Interaction?

• Controversy still remains: Corrected 4P/2P ratio for C4+ either

too large (WMU) or too small (APAPES)!• New results even more controversial! Still preliminary – need to be checked further

APAPES Main team

• Dept. of Physics, Univ. of Crete, Heraklion

Theo Anastasios Ioannis Angelos Zouros Dimitriou Madesis Laoutaris (Prof & PI) (PostDoc) (PhD student) (MS student) CDAMOP Delhi Mar 12, 2015

APAPES important

participants


Manolis Bela Omer Genoveva Jose Benis Sulik Sise Martinez-Lopez Paulo Santos (Prof) (Prof) (Prof) (Prof) (Prof)

Dept of PhysicsUniv of Ioannina

Greece

ATOMKIDebrecenHungary

Univ of IspartaTurkey

Dept Fisica Aplicada Madrid,

Spain

Dept de FisicaUniv Nova de Lisboa

Portugal

CPO simulationsZoom lenses

AtomicStructure

calculations

SpirosDoukas

U. Ioannina

SIMION

Measurements

APAPESSupport

Team

5MV Tandem, Institute of Nuclear and Particle Physics NCSRT Demokritos

Dr. Sotiris Dr. Tasos Dr. Michalis Miltos Theo Harissopulos Lagoyannis Axiotis Andrianis Mertzimekis (Director) (Res.) (Res.) (Accel. Eng.) (Prof.)

Univ. of Athens


The end thank you for listeningI thank the organizers

for inviting me

More info? Please Contact me: [email protected]


Acknowledgement: This research has been co-financed by the European Union (European Social Fund ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) Research Funding Program: THALES. Investing

in knowledge society through the European Social Fund, grant number MIS 377289.

high resolution auger projectile electron spectroscopy of li-like ions produced by electron capture...

Documents