Positronium Negative Ions

Positronium Negative Ions

Yasuyuki NAGASHIMADepartment of Physics

Tokyo University of ScienceJAPAN 1

Our studies for Ps －

We started Ps － experiments in Tokyo Univ. of Sci. in 2005.

Observation of Ps － emission from tungsten surfaces(Nagashima et al., New J. Phys. 8 (2006) 319; Mat. Sci. Forum 607 (2009) 161)

Efficient emission of Ps － using Cs coated tungsten surface(Nagashima et al., New J. Phys. 10 (2008) 123029; Phys. Status Solidi C 6 (2009)

2291) Emission of Ps － from Mo and Ta surfaces

(Michishio et al., J. Phys. Conf. Ser. 199 (2010) 012003) Durable emission of Ps － from Na coated tungsten surface

(Terabe et al., J. Phys. Conf. Ser. 262 (2011) 012058, also in preparation) Ps － photodetachment experiment

(Michishio et al., Phys. Rev. Lett. 106 (2011) 153401) Detection of Ps formed by the Ps － photodetachment

(Koji Michishio, O-19, on Wednesday)2

OUTLINE OF THIS TALK

What is Ps － ?

Efficient emission of Ps － using Cs coated tungsten surface

Emission of Ps － from Mo and Ta surfaces

Durable emission of Ps － from Na coated tungsten surface

Ps － photodetachment experiment

Future plans

Conclusions

3


What is Ps － ?





Future plans

Conclusions

4

Theoretical studies have been started.(Frolov, Phys. Lett. A 372 (2008) 6721)Nobody has produced.

Existence has been reported.(Cassidy and Mills, Nature 449 (2007) 06094)

Existence has been confirmed.

Bound states composed of e+ and e －

e+ e － Ps

e+

e －

e+ e －

e+ e －

e －

e+

Ps

Ps Ps

Ps Ps

Ps＝

positronium 　 (Ps)

positronium negative ion 　 (Ps － )

positronium plus ion 　 (Ps ＋ )

positronium molecule 　 (Ps2)

bi-positronium negative ion 　 (Ps2e － )

bi-positronium positive ion 　 (Ps2e ＋ )

5

e － e+ e －

　 positronium negative ion (Ps－ )

H － ion like state

All the constituents of Ps －

　　　　　　　　　　 have the same mass.

The theoretical approach for H －

(Born-Oppenheimer approximation)CANNOT be used for Ps － .

Many theoretical approaches using variational principles have been performed.

　 positronium (Ps)

H atom like state

The theoretical approach for H atoms can be applied.

The wave function can be obtainedwithout any approximations.

6

e － e+ e －


e － binding energy to Ps = 0.33eV; Total binding energy (the energy required to break up Ps － into 3 isolated particles) : 0.33eV + 6.80eV = 7.13eV Mean distance 　 e+ － e － : 5.5a0

Only one state Lifetime in vacuum : 479ps Self-annihilates into 2γ.

　 positronium (Ps)

Binding energy : 6.80eV

Mean distance 　 e+ － e － : 2a0

Two eigenstates ortho-Ps (S=1, triplet) lifetime in vacuum : 142ns Self-annihilates into 3γ . para-Ps (S=0, singlet) lifetime in vacuum : 125ps Self-annihilates into 2γ .

7

　　　　　　　　　　　　 History of Ps － research

　　　　 1946 J.A. Wheeler predicted the existence.　　　　

e － e+ e －


Many theoretical researches have been performed since the prediction of Wheeler.

8

1960 Calculation of the Ps- binding energy by Kolos, Rootrhaan and Sack.1964 Calculation of the Ps- binding energy by Frost, Inokuti and Lowe.1968 Calculation of the Ps- decay rate by Ferrante.1979 Calculation of the Ps- binding energy by Ho.1983 Calculation of the Ps- binding energy and decay rate by Bhatia andDrachman.1985 Calculation of Ps- photodetachment cross sections by Bhatia and Drachman.1987 Calculation of Ps- photodetachment cross sections by Ward,

Humberston and McDowell.1990 Calculation of the Ps- decay rate by Ho.1993 Calculation of Ps- binding energy by Ho.2000 Calculation of the Ps- binding energy by Korobov.2000 Calculation of Ps- photodetachment cross sections by Igarashi, Shimamura and Toshima.2002 Calculation of Ps- binding energy by Drake, Grigorescu and Nistor. 2005 Calculation of the Ps- binding energy by Drake and Grigorescu.

EB ＝　 0.261 998 108 122 au ~ 7.129 330 97 eV2007 Calculation of the Ps- decay rate by Puchalski and Czanecki.

Γ= 2.087 963 (12) ns-1.

Examples of theoretical investigations on Ps － :


　　　　 1946 J.A. Wheeler predicted the existence.　　　　 1981 A. P. Mills, Jr. succeeded in the production.　　　　　　　　　　　　 (formation efficiency=0.028%)　　　　

Ps － formation efficiency ＝ number of formed Ps － /number of incident slow e+

e － e+ e －


11

• Slow positrons (470 eV) were guided to a thin carbon target.

• Ps － emitted were accelerated by the electric field and detected by their Doppler-shifted annihilation lines.

(A.P. Mills, Jr., Phys. Rev. Lett. 46 (1981) 717)

First observation of Ps － (Mills, 1981)

Ps － formation efficiency = 0.028%

θ

Ps － formation was confirmed.

12

Measurement of the Ps － decay rate

13

Γ ＝ 2.09±0.09ns-1

A. P. Mills, Phys. Rev. Lett. 50 (1983) 671

14

Tandem acceleration method of detecting Ps －

A. P. Mills, Jr., P. G. Freeman and D. M. Zuckerman, NASA Conference Publication (1989)


(Fleischer et al., Phys. Rev. Lett. 96 (2006) 063401)

1)015.0089.2( ns

Ps- fraction = 1 x 10-4

（ 30eV ）

Stripping-baseddetection technique



　　　　 1946 J.A. Wheeler predicted the existence.　　　　 1981 A. P. Mills, Jr. succeeded in the production.　　　　　　　　　　　　 (formation efficiency=0.028%) Many theoretical researches have been performed.　　　　

e － e+ e －


Only a few experiments have been performed.

Ps － formation efficiency is too low. 16


What is Ps － ?





Future plans

Conclusions

17

e+ near metal surface

Diffusion length of e+ in defect free metals~ 100nm

A significant fraction of e+ incident onto surface with a few keV energy

diffuse back to the surface.

When e+ are incident onto metal surfaces, ...

annihilation cross section 　　　 << collision cross section e+ lifetime in metals ~ 100ps

18

： e+ work function

(The energy required to emit e+)

0

e+ are emitted from the surface.

20

eV80.6Ps

: e+ work function : e － work function

0Ps

Ps atoms are emitted from the surface.

The energy required to emit Ps :

21

eV13.72Ps

The energy required for Ps － emission :

0Ps

Ps － might be emittedfrom the surface spontaneously.

Ps － binding energy(The energy required to break up Ps － into three isolated particles)

e － work function

e+ work function

22

Element Φ+ (eV) Φ- (eV) ΦPs- (eV)

Al (polycrystalline) -0.2 4.25 1.2Al (1 0 0) -0.16 4.20 1.11Al (1 1 1) 0.065 4.26 1.46Cr (1 0 0) -1.76 4.46 0.03Fe (polycrystalline) -1.2 4.4 0.5Co (polycrystalline) -0.8 5.0 2.1Ni (polycrystalline) -1.2 5.15 2.0Ni (1 0 0) -1.0 5.22 2.3Ni (1 1 0) -1.4 5.04 1.6Cu (1 0 0) -0.3 5.10 2.8Cu (1 1 0) -0.2 4.48 1.6Cu (1 1 1) -0.4 4.94 2.4Mo (polycrystalline) -2.2 4.6 -0.1Mo (1 0 0) -1.7 4.53 0.2Ta (polycrystalline) -1.2 4.25 0.2W (polycrystalline) -2.75 4.55 -0.78W (1 0 0) -3.0 4.63 -0.9W (1 1 0) -3.0 5.22 0.3W (1 1 1) -2.59 4.45 -0.82Pt (polycrystalline) -1.8 5.64 2.4Au (polycrystalline) 0.9 5.2 4.2Pb (polycrystalline) 0.9 4.25 2.3

polycrystalline molybdenum tungsten (1 0 0) tungsten (1 1 1) polycrystalline tungsten

Ps － ions may be emitted.

23

polycrystalline molybdenum tungsten (1 0 0) tungsten (1 1 1) polycrystalline tungsten

Ps － ions may be emitted.

24


Al (polycrystalline) -0.2 4.25 1.2Al (1 0 0) -0.16 4.20 1.11Al (1 1 1) 0.065 4.26 1.46Cr (1 0 0) -1.76 4.46 0.03Fe (polycrystalline) -1.2 4.4 0.5Co (polycrystalline) -0.8 5.0 2.1Ni (polycrystalline) -1.2 5.15 2.0Ni (1 0 0) -1.0 5.22 2.3Ni (1 1 0) -1.4 5.04 1.6Cu (1 0 0) -0.3 5.10 2.8Cu (1 1 0) -0.2 4.48 1.6Cu (1 1 1) -0.4 4.94 2.4Mo (polycrystalline) -2.2 4.6 -0.1Mo (1 0 0) -1.7 4.53 0.2Ta (polycrystalline) -1.2 4.25 0.2W (polycrystalline) -2.75 4.55 -0.78W (1 0 0) -3.0 4.63 -0.9W (1 1 0) -3.0 5.22 0.3W (1 1 1) -2.59 4.45 -0.82Pt (polycrystalline) -1.8 5.64 2.4Au (polycrystalline) 0.9 5.2 4.2Pb (polycrystalline) 0.9 4.25 2.3

NaIGROUNDE D GRID

PM T

DI SC.

MCAAMP

TUNGSTE N TARGE T

Ps-e+d

PbGe

I NPUT

P.U.R.

SCALE:

COI NC.

0 5 10cm

W-

HAMAMATSU H6614101

103

105

Cou

nts

(d) Annealed, W=3kV

0

50

100 (c) Annealed, W=3kV

0

50

100 (b) Annealed, W=1kV

500 520 540 560 5800

50

100

Energy (keV)

(a) Unannealed, W=1kV

Ps － emission from polycrystalline tungsten surface(Nagashima and Sakai, New J. Phys. 8 (2006) 319)

Ps － formation efficiency was only 0.007%.(1/4 of that of beam-foil method)

vacuum : 7 x 10-8 Pa (5 x 10-10 torr)

26

101

103

105

Cou

nts

(d) Annealed, W=3kV

0

50

100 (c) Annealed, W=3kV

0

50

100 (b) Annealed, W=1kV

500 520 540 560 5800

50

100

Energy (keV)

(a) Unannealed, W=1kV

(Nagashima and Sakai, New J. Phys. 8 (2006) 319)

0 10 20 30 40 50 600

2

4

6

8

10

Time after annealing (h)

( x 1

0-5 )

Ps- fr

actio

n

Ps － formation efficiency decreases.

Change of the surface condition

Ps － emission from polycrystalline tungsten surface

27

e － energy level e+ energy lebel(Achcroft and Mermin) (Schultz and Lynn, Rev. Mod. Phys. 60 (1988) 701)

e － and e+ near metal surface

D

e － work function : e+ work function :D D

D

： e － chemical potential

： e+ chemical potential： effect of surface dipole

D

28

0 10 20 30 40 50 600

2

4

6

8

10

Time after annealing (h)

( x 1

0-5 )

Ps- fr

actio

n

D becomes largerby the effect of oxygen, H, H2O, .....


.eV13.72Ps

D

Ps － formation efficiency decreases.

D

D

eV13.72Ps

29


When the vacuum was improved, the fraction became stable.

7 x 10-8 Pa 3 x 10-8 Pa

Time dependence of Ps- formation efficiency


When the vacuum was improved, the fraction became stable.

7 x 10-8 Pa 3 x 10-8 Pa

(Nagashima and Sakai, New J. Phys. 8 (2006) 319,Nagashima, Hakodate and Sakai, Appl. Surf. Sci. 255 (2008) 217)

The dependence was due to the adsorbate coverage of the target surfaceby residual molecules in the target chamber.

Time dependence of Ps- formation efficiency

Effect of Cs coating for the Ps － emission

eV13.72Ps D

Kiejna and Wojciechowski, Prog. in Surf. Sci. 11 (1981) 293

D decreases.

Change of for tungsten by Cs coating

Ps － formation efficiency might increase.

D decreases by Cs coating.

Ps

decreases.

32

e+ transport energy ： 100eVe+ incident energy onto the target : 100eV + eW

Target 　 W(100)

vacuum ： 2×10-8Pa（ 1.5×10-10torr ）

Target was annealed at 1500 for 30 min.℃

target potential ： -3kV

(Nagashima et al. New J. Phys. 10 (2008) 123029)


34

(Nagashima et al. New J. Phys. 10 (2008) 123029)


35

Ps － intensity is the highestat 2.2×1014cm-2 （ 0.8ML).


Change of for tungsten by Cs coating


36

The highest efficiency was 1.25%,

which is two orders of magnitude higherthan that obtained for uncoated surface,

and 45 times greaterthan the beam-foil method.


37


What is Ps － ?





Future plans

Conclusions

38


Al (polycrystalline) -0.2 4.25 1.2Al (1 0 0) -0.16 4.20 1.11Al (1 1 1) 0.065 4.26 1.46Cr (1 0 0) -1.76 4.46 0.03Fe (polycrystalline) -1.2 4.4 0.5Co (polycrystalline) -0.8 5.0 2.1Ni (polycrystalline) -1.2 5.15 2.0Ni (1 0 0) -1.0 5.22 2.3Ni (1 1 0) -1.4 5.04 1.6Cu (1 0 0) -0.3 5.10 2.8Cu (1 1 0) -0.2 4.48 1.6Cu (1 1 1) -0.4 4.94 2.4Mo (polycrystalline) -2.2 4.6 -0.1Mo (1 0 0) -1.7 4.53 0.2Ta (polycrystalline) -1.2 4.25 0.2W (polycrystalline) -2.75 4.55 -0.78W (1 0 0) -3.0 4.63 -0.9W (1 1 0) -3.0 5.22 0.3W (1 1 1) -2.59 4.45 -0.82Pt (polycrystalline) -1.8 5.64 2.4Au (polycrystalline) 0.9 5.2 4.2Pb (polycrystalline) 0.9 4.25 2.3 39

Ps － emission from Cs coated Mo surfaces

Ps － ions were detected for uncoated Mo and Cs coated Mo.

2 x 1014 atoms/cm2



2 x 1014 atoms/cm2

First experimental evaluation for EB



2 x 1014 atoms/cm2

B

BPs

E

E 2

： Ps- binding energy

　　 for the uncoated Mo surface.0Ps

eV0.72 BE


Al (polycrystalline) -0.2 4.25 1.2Al (1 0 0) -0.16 4.20 1.11Al (1 1 1) 0.065 4.26 1.46Cr (1 0 0) -1.76 4.46 0.03Fe (polycrystalline) -1.2 4.4 0.5Co (polycrystalline) -0.8 5.0 2.1Ni (polycrystalline) -1.2 5.15 2.0Ni (1 0 0) -1.0 5.22 2.3Ni (1 1 0) -1.4 5.04 1.6Cu (1 0 0) -0.3 5.10 2.8Cu (1 1 0) -0.2 4.48 1.6Cu (1 1 1) -0.4 4.94 2.4Mo (polycrystalline) -2.2 4.6 -0.1Mo (1 0 0) -1.7 4.53 0.2Ta (polycrystalline) -1.2 4.25 0.2W (polycrystalline) -2.75 4.55 -0.78W (1 0 0) -3.0 4.63 -0.9W (1 1 0) -3.0 5.22 0.3W (1 1 1) -2.59 4.45 -0.82Pt (polycrystalline) -1.8 5.64 2.4Au (polycrystalline) 0.9 5.2 4.2Pb (polycrystalline) 0.9 4.25 2.3 43

Ps － emission from Cs deposited Ta surfaces

Ps － ions were not detected for uncoated Ta,

Ps － ions were detected for the Cs coated Ta.

The efficiency was 1.5%,which is higher than that for the Cs coated

W(100).

but

2 x 1014 atoms/cm2


Ps － ions were not detected for uncoated Ta.2 x 1014 atoms/cm2

B

BPs

E

E 2

： Ps － binding energy

　　 for the uncoated Ta surface.0Ps

eV3.72 BE


Ps － ions were not detected for uncoated Ta.2 x 1014 atoms/cm2

B

BPs

E

E 2

： Ps － binding energy

　　 for the uncoated Ta surface.0Ps

eV3.72 BE

eV3.7eV0.7 BE


What is Ps － ?





Future plans

Conclusions

48


Time dependence of f

carbon film

The decrease might be due tothe accumulation of residual molecules.

49

Effect of K and Na coating for the Ps － emission


K and Na are less reactive chemically than Cs.

Ps － emission might stay longer.

The effect might be smaller.

50

Cs K Na


51

Na coating is as effectiveand the effect remains LONGER!


52


What is Ps － ?





Future plans

Conclusions

53

Theoretical investigations for the photodetachment of Ps － :

1985 Calculation of the photodetachment cross sections by Bhatia and Drachman

1987 Calculation of the photodetachment cross sections by Ward, Humberston and

McDowell

2000 Calculation of the photodetachment cross sections by Igarashi, Shimamura and

Toshima

（ Igarashi et al, New J. Phys. 2 (2000) 17 ）

55

High intensity pulsed laser Pulsed e+ beamsynchronized to the laser


56

Ps － lifetime is 479ps.

http://www-linac.kek.jp/slowpos/OVERVIEW.PDF

Pulsed e+ beam in KEK

57

Pulsed e+ beam in KEK

58

e+ beam :　　 (from KEK Linac)　　 pulse width 12ns　　 repetition 50Hz

　

Laser :　　 Pulsed Nd: YAG　　 (Spectra Physics GCR290)　　 wave length 1064nm　　 pulse width 12ns　　 repetition 25Hz　　 power 10W


(Michishio, Tachibana, Terabe, Igarashi, Wada, Hyodo, Kuga, Yagishita, Hyodo and NagashimaPhys. Rev. Lett. 106 (2011) 153401) 59

(Bhatia and Drachman, Phys. Rev. A 32 (1985) 3745,Ward, Humberston and McDowell, J. Phys. B 20 (1987) 127,Igarashi, Shimamura and Toshima, New J. Phys. 2 (2000) 17)


1064nm

Threshold : 0.33eV

60

e+ beam :　　 (from KEK Linac)　　 pulse width 12ns　　 repetition 50Hz　

Laser :　　 Pulsed Nd: YAG　　 (Spectra Physics GCR290)　　 wave length 1064nm　　 pulse width 12ns　　 repetition 25Hz　　 power 10W


(Michishio, Tachibana, Terabe, Igarashi, Wada, Hyodo, Kuga, Yagishita, Hyodo and NagashimaPhys. Rev. Lett. 106 (2011) 153401) 61

(Michishio, Tachibana, Terabe, Igarashi, Wada, Hyodo, Kuga, Yagishita, Hyodo and NagashimaPhys. Rev. Lett. 106 (2011) 153401)

Ps－

75% o-Ps, annihilates into 3γ.

25% p-Ps, annihilates into 2γ.

If Ps － ions are photodetached,the peak intensity will decrease.


62


Ps － photodetachment has been observed for the first time!

Ps－

75% o-Ps, annihilates into 3γ.

25% p-Ps, annihilates into 2γ.

If Ps － ions are photodetached,the peak intensity will decrease.


63



64


What is Ps － ?





Future plans

Conclusions

65


What is Ps － ?





Future plans

Conclusions

66

Measurement of the photodetachment cross sections

Production of energy tunable Ps beam

Precision measurement of the Ps － decay rate

67

Measurement of the Ps － photodetachment cross sections


（ Igarashi et al, New J. Phys. 2 (2000) 17 ） 68

Measurement of the Ps － photodetachment cross sections

resonances

Production of energy tunable Ps beam using Ps － photodetachment technique and its applications

69

“Production of an energy tunable positronium beamby the photodetachment of positronium negative ions”

by Koji Michishio on Wednesday


70

Γ ＝ 2.09±0.09ns-1

A. P. Mills, Phys. Rev. Lett. 50 (1983) 671

(Fleischer et al., Phys. Rev. Lett. 96 (2006) 063401)

1)015.0089.2( ns

Ps- fraction = 1 x 10-4

（ 30eV ）

Stripping-baseddetection technique


By changing the distance and voltage between the target and the earthed grid, we aim high precision measurement with the error ～ 0.1%

Ne dispenser

Precision measurement of the Ps － decay rate

(1) We have succeeded in the efficient formation Ps － .

(2) We have succeeded in the first estimation of the binding energy of Ps － .

(3) We have succeeded in first observation of the photodetachment of Ps － .

(4) We have started the next experiments for Ps － .

CONCLUSIONS

73

Member of our group

Tokyo University of Science

Koji Michishio, Takayuki TachibanaHiroki Terabe, Ryohei Suzuki

Ayaka Miyamoto, Toshihide HakodateTakahiko Sakai

Akira Yagishita (KEK)Toshio Hyodo (KEK)

Ken Wada (KEK)Akinori Igarashi (Miyazaki Univ.)Takahiro Kuga (Univ. of Tokyo)

74

Thank you very much for your attention !

75

Why Ps- fraction increased dramatically?

021 BE holds for the Ps- emission,

If we assume that the Ps- is formed from positrons in the bottom of the positron band,

where and are the energy levels of two electrons measured from the vacuum level.1 2

22111

dDdDf

BB EE

Ps- fraction :

D : electron density of states

V A C U U M L E V E L

VA C U U M L E V E L

φ -E (= -1 0 .1 e V )

- ( = - 4 .6 e V )φ

- ' ( = -1 .5 e V )φ

φ ' -E ( = - 7 . 0 e V )

+

-

-

+

B

B

φ - E + B φ ' - E + B -φ - - 'φ -

ε1

ε 2.21

)()(

uncoatedfdepositionCswithf

This is too low to explain the experimental results.

If is constant below the top of the conduction band,

D

77

The Ps- formation depends on the overlap of a e+ wave functionand two e- wave functions just outside of the surface,which depend on their corresponding work functions.

surfacebulk vacuum

e+

e

e

-

-

e+ and e- wave functions

Cs deposited

uncoated

The Ps- formation mechanism should be affected

by the Cs deposition.

Why Ps- fraction increased dramatically?

78

MMe Ps

PsIePs EETT ./eV8.6 2nEPs

(Brown, Positron Annihilation (1985) 328)

Ps 生成の微分断面積は前方にピークを持つ

, where

エネルギー可変 Ps ビーム

e+ ビームと気体分子との電荷交換反応

79

(Weber et al., Phys. Rev. Lett. 61 (1988) 2542)

応用例： LiF 表面での Ps の鏡面反射


80

(Mills and Crane, Phys. Rev. A 31 (1985) 593)

ddEEdN 2/32/13 )eV10(

Ps energy distribution:


81

Positronium Negative Ions

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