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Page 1: Ge 74 Gamma-ray strength functions in

Text optional: Institutsname Prof. Dr. Hans Mustermann www.fzd.de Mitglied der Leibniz-GemeinschaftRonald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Gamma-ray strength functions in 74Ge

Ronald Schwengner

Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf

01328 Dresden, Germany

• Dipole strength up to the neutron-separation energy:

- Photon-scattering experiments at γELBE

• M1 and E2 strength at low energy:

- Shell-model calculations

Page 2: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Study of germanium isotopes

Extraction of neutron-capture cross sections for astrophysically relevant neutronenergies.

Test of strength functions deduced from different reactions.

Combination of experiments using neutron capture and alternative reactiontechniques in an international collaboration:

– Neutron capture at IKI Budapest.

– Discrete γ-ray spectroscopy at STARS-LIBERACE (LBNL)and AFRODITE (iThemba).

– Statistical γ-ray measurements at CACTUS (Oslo)and γELBE (HZDR).

Page 3: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

The bremsstrahlung facility at the electron accelerator ELBE

Accelerator parameters:

• Maximum electron energy:

≈ 18 MeV

• Maximum average current:

≈ 0.8 mA

• Micro-pulse rate:

13 MHz

• Micro-pulse length:

≈ 5 ps

R.S. et al., NIM A 555, 211 (2005)

1 m

Be window

dipole

dipole

dipole

radiator

steerer

quadrupoles

quadrupole

electron-beam dump

quartz windowbeam

hardener

collimator

polarisationmonitor

target

PbPE

door

Pb

photon-beamdump

Pb

HPGe detector

experimentalcave

acceleratorhall

Page 4: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Detector setup at γELBE

Page 5: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Measurement at γELBE

1 2 3 4 5 6 7 8 9 10 11Eγ (MeV)

105

106

107

108

109

Cou

nts

per

10 k

eV experimental spectrum

74Ge(γ,γ’) Ee

kin = 12.1 MeV θ = 127

o

Page 6: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Measurement at γELBE

1 2 3 4 5 6 7 8 9 10 11Eγ (MeV)

105

106

107

108

109

Cou

nts

per

10 k

eV experimental spectrum

74Ge(γ,γ’) Ee

kin = 12.1 MeV θ = 127

o

response−corrected

Page 7: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Measurement at γELBE

1 2 3 4 5 6 7 8 9 10 11Eγ (MeV)

105

106

107

108

109

Cou

nts

per

10 k

eV experimental spectrum

atomic background

74Ge(γ,γ’) Ee

kin = 12.1 MeV θ = 127

o

response−corrected

Page 8: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Photon scattering - feeding and branching

0Γ0

Γ1

E ,x Γ

branchingΓf

Ee

Measured intensity of a γ transition:

Iγ(Eγ, Θ) = Is(Ex) Φγ(Ex) ǫ(Eγ) Nat W (Θ) ∆Ω

Integrated scattering cross section:

Is =

σγγ dE =2Jx + 1

2J0 + 1

(

πhc

Ex

)2Γ0

ΓΓ0

Absorption cross section:

σγ = σγγ

(

Γ0

Γ

)

−1

E1 strength:

B(E1) ∼ Γ0/E 3

γ

Page 9: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Photon scattering - feeding and branching

0Γ0

Γ1

Ee

E ,x Γ

branchingΓf

feeding

Measured intensity of a γ transition:

Iγ(Eγ, Θ) > Is(Ex) Φγ(Ex) ǫ(Eγ) Nat W (Θ) ∆Ω

Integrated scattering cross section:

Is =

σγγ dE =2Jx + 1

2J0 + 1

(

πhc

Ex

)2Γ0

ΓΓ0

Absorption cross section:

σγ = σγγ

(

Γ0

Γ

)

−1

E1 strength:

B(E1) ∼ Γ0/E 3

γ

Page 10: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Simulations of γ-ray cascades

Code γDEX:

G. Schramm et al., PRC 85, 014311 (2012)

R. Massarczyk et al., PRC 86, 014319 (2012);

PRC 87, 044306 (2013)

0

Γ0 Γ1 2Γ

Γ JE π

⇒ Level scheme of J = |J0±1, ..., 5| states in 10 keV

energy bins constructed by using:

Constant-Temperature Model with level-density

parameters from T. v. Egidy, D.Bucurescu, PRC

80, 054310 (2009).

Parity distribution of level densities according to

S. I. Al-Quraishi et al., PRC 67, 015803 (2003).

Wigner level-spacing distributions.

⇒ Partial decay widths calculated by using:

Photon strength functions approximated by

Lorentz curves (www-nds.iaea.org/RIPL-2).

Porter-Thomas distributions of decay widths.

⇒ Subtraction of feeding intensities and correction

of intensities of g.s. transitions with calculated

branching ratios Γ0/Γ .

⇒ Determination of the absorption cross section.

Page 11: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Average branching ratios of ground-state transitions in 74Ge

1 2 3 4 5 6 7 8 9 10 11Ex (MeV)

0

20

40

60

80

100

b 0∆ (%

)

74Ge

Page 12: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Iterative determination of the absorption cross section

3 4 5 6 7Ex (MeV)

0

1

2

3

σ γ (m

b)

74Ge(γ,γ’)

7.5 MeV

uncorr.

5 6 7 8 9 10 11Ex (MeV)

0

5

10

σ γ (m

b)

74Ge(γ,γ’)

12.5 MeV

Sn

uncorr.

Cross section including strength of resolved peaks and of quasi-continuum.

Page 13: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Iterative determination of the absorption cross section

3 4 5 6 7Ex (MeV)

0

1

2

3

σ γ (m

b)

74Ge(γ,γ’) 1. iteration

7.5 MeV

uncorr.

5 6 7 8 9 10 11Ex (MeV)

0

5

10

σ γ (m

b)

74Ge(γ,γ’)

1. iteration

12.5 MeV

Sn

uncorr.

Cross section including strength of resolved peaks and of quasi-continuum.

Result of the correction for feeding intensities and branching ratios used as input for the next calculation.

Page 14: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Iterative determination of the absorption cross section

3 4 5 6 7Ex (MeV)

0

1

2

3

σ γ (m

b)

74Ge(γ,γ’) 1. iteration

7.5 MeV

4. iteration

uncorr.

5 6 7 8 9 10 11Ex (MeV)

0

5

10

σ γ (m

b)

74Ge(γ,γ’)

1. iteration

12.5 MeV

Sn

5. iteration

uncorr.

Cross section including strength of resolved peaks and of quasi-continuum.

Result of the correction for feeding intensities and branching ratios → used as input for the next calculation.

Convergence criteria fulfilled → data taken as final results.

Page 15: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Absorption cross section of 74Ge

3 4 5 6 7 8 9 10 11Ex (MeV)

0

2

4

6

8

10

σ γ (m

b)

74Ge(γ,γ’)

7.5 MeV

12.5 MeV

Sn

Page 16: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Absorption cross section of 74Ge

0 5 10 15 20 25Ex (MeV)

100

101

102

σ γ (m

b)

74Ge

(γ,γ’)7.5 MeV

(γ,γ’)12.5 MeV

Page 17: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Absorption cross section of 74Ge

0 5 10 15 20 25Ex (MeV)

100

101

102

σ γ (m

b)

74Ge

(γ,γ’)7.5 MeV

(γ,γ’)12.5 MeV

(γ,x)

(γ,x) data:

P. Carlos et al.,

NPA 258, 365 (1976)

Page 18: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Absorption cross section of 74Ge

0 5 10 15 20 25Ex (MeV)

100

101

102

σ γ (m

b)

74Ge

(γ,γ’)7.5 MeV

(γ,γ’)12.5 MeV

TLO(γ,x)

(γ,x) data:

P. Carlos et al.,

NPA 258, 365 (1976)

TLO (β2 = 0.28, γ = 27):

A. Junghans et al.,

PLB 670, 200 (2008)

Page 19: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Electromagnetic strength functions

Electromagnetic strength functions (photon strength functions) describe averageelectromagnetic transitions strengths - in particular in the quasi-continuum of nuclearstates at high excitation energy:

ffiL(Eγ) = ΓfiL ρ(Ei , Ji) / E2L+1

γ Eγ = Ei − Ef Ji = 0, ..., Jmax

Photoabsorption:

fL = σγ / [(2Ji+1)/(2J0+1) (πhc)2E

2L−1

γ ] Eγ = Ei Ji = 1, (2)

Brink-Axel hypothesis:The strength function does not depend on the excitation energy.The strength function for excitation is identical with the one for deexcitation.

Page 20: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Dipole strength functions in 74Ge

0 2 4 6 8 10 12Eγ (MeV)

100

101

102

f 1 (1

0−9 M

eV−

3 )

74Ge

(γ,γ’)7 MeV (γ,γ’)12 MeV

Page 21: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Dipole strength functions in 74Ge

0 2 4 6 8 10 12Eγ (MeV)

100

101

102

f 1 (1

0−9 M

eV−

3 )

74Ge (

3He,

3He’)

(γ,γ’)7 MeV (γ,γ’)12 MeV

(3He,3He’) data:

T. Renstrøm et al.

Page 22: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Dipole strength functions in 74Ge

0 2 4 6 8 10 12Eγ (MeV)

100

101

102

f 1 (1

0−9 M

eV−

3 )

74Ge (

3He,

3He’)

(γ,γ’)7 MeV (γ,γ’)12 MeV

TLO

(3He,3He’) data:

T. Renstrøm et al.

Page 23: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Dipole strength functions in 74Ge

0 2 4 6 8 10 12Eγ (MeV)

100

101

102

f 1 (1

0−9 M

eV−

3 )

74Ge (

3He,

3He’)

(γ,γ’)7 MeV (γ,γ’)12 MeV

TLO GLO

(3He,3He’) data:

T. Renstrøm et al.

Page 24: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Shell-model calculations of M1 strength functions

0 2 4 6 8 10 12 14 16Eγ (MeV)

10−2

10−1

100

101

102

103

f 1 (1

0−9 M

eV−

3 )

94Mo

(3He,

3He’) data

shell modelM1

E1 + M1 (γ,n) data

E1

)-3

(M

eV

M1

f

-910

-810

-710

Fe, Voinov et al. (2004) 56

)γαHe,3

(

Fe, Larsen et al. (2013) 56

)γ (p,p'

SM calc

Fe56

(a)

(MeV)γE0 1 2 3 4 5 6 7

)-3

(M

eV

M1

f-9

10

-810

-710

Fe57

(b)Fe, Voinov et al. (2004)

57)γHe'

3He,

3 (

Fe, Larsen et al. (2013/2014) 57

)γ (p,p'

SM calc

RITSSCHIL NuShellX

R.S., S. Frauendorf, A.C. Larsen

PRL 111, 232504 (2013)

B.A. Brown, A.C. Larsen

PRL 113, 252502 (2014)

Page 25: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Generation of large M1 strengths

J + 1

J

J π

ν

J π

J ν

J

M1

⇒ Configurations including protons and neutrons in specific high-j orbits with large magneticmoments.

⇒ Coherent superposition of proton and neutron contributions for specific combinations ofgπ and g ν factors and relative phases (“mixed symmetry”).

⇒ Large M1 strengths appear between states with equal configurations by a recoupling ofthe proton and neutron spins (analog to the “shears mechanism”).

Page 26: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Dipole strength functions in 74Ge

0 2 4 6 8 10 12Eγ (MeV)

10−1

100

101

f 1 (1

0−9 M

eV−

3 ) 74Ge(

3He,

3He’)

GLO(3He,3He’) data:

T. Renstrøm et al.

Page 27: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Dipole strength functions in 74Ge

0 2 4 6 8 10 12Eγ (MeV)

10−1

100

101

f 1 (1

0−9 M

eV−

3 )

74Ge

74Ge(

3He,

3He’)

M1 calc.

GLO(3He,3He’) data:

T. Renstrøm et al.

RITSSCHIL

Page 28: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Dipole strength functions in 74Ge

0 2 4 6 8 10 12Eγ (MeV)

10−1

100

101

f 1 (1

0−9 M

eV−

3 )

74Ge

74Ge(

3He,

3He’)

M1 calc.

80Ge GLO

(3He,3He’) data:

T. Renstrøm et al.

RITSSCHIL

Page 29: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Predicted Appearance of magnetic rotation

0 20 40 60 80 100 120 140 160020406080100120140

Neutron Number N

ProtonNumberZ j"2j0.250.1528 50 82 12628 50 8264 642020

qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . ...............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

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....................................................................................................................................................S. Frauendorf, Rev. Mod. Phys. 73, 463 (2001).

Page 30: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Generation of large M1 strengths

B(M1) ∼ µ2

Analogous “shears mechanism”

in magnetic rotation

S. Frauendorf, Rev. Mod. Phys. 73, 463 (2001).

Examples near A = 80: 82Rb, 84Rb

H. Schnare et al., PRL 82, 4408 (1999).

R.S. et al., PRC 66, 024310 (2002).

Page 31: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Shell-model calculations for 74Ge and 80Ge

Main configurations that generate large M1 transition strengths(active orbits with jπ 6= 0 and jν 6= 0):

74Ge π = +: π(0f45/2

) ν(0g2

9/2) π = –: π(0f4

5/2) ν(1p−1

1/20g3

9/2)

π(0f35/2

1p1

3/2) ν(0g2

9/2) π(0f3

5/21p1

3/2) ν(1p−1

1/20g3

9/2)

π(0f25/2

1p2

3/2) ν(0g2

9/2) π(0f2

5/21p2

3/2) ν(1p−1

1/20g3

9/2)

80Ge π = +: π(0f45/2

) ν(0g8

9/2) π = –: π(0f3

5/20g1

9/2) ν(0g8

9/2)

π(0f35/2

1p1

3/2) ν(0g8

9/2) π(0f2

5/21p1

3/20g1

9/2) ν(0g8

9/2)

π(0f35/2

1p1

3/2) ν(0g7

9/21d1

5/2) π(0f3

5/20g1

9/2) ν(0g7

9/21d1

5/2)

⇒ Configurations including a broken ν0g9/2 pair in addition to π(fp) excitations.

Page 32: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

E2 strength function in 94Mo

0 2 4 6 8 10 12 14 16Eγ (MeV)

100

101

102

f 2 (1

0−12

MeV

−5 )

94Mo

RIPL

E2 strength function in RIPL

Lorentz curve with:

Emax = 63 A−1/3 MeV

Γ = 6.11 – 0.021A MeV

σγ,max = 0.00014 Z2EmaxA

−1/3Γ−1 mb

R.S., PRC 90, 064321 (2014)

Page 33: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

E2 strength function in 94Mo

0 2 4 6 8 10 12 14 16Eγ (MeV)

100

101

102

f 2 (1

0−12

MeV

−5 )

94Mo

RIPL

shell model

E2 strength function

f2 = 0.80632 B(E2) ρ(Ex ,J)

ρ(Ex , J) - level density

of the shell-model states,

includes π = ± 1,

J = 0 to 10,

40 states for each Jπ.

RITSSCHIL

R.S., PRC 90, 064321 (2014)

Page 34: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

E2 strength function in 94Mo

0 1 2 3 4 5 6Eγ (MeV)

0

5

10

B(E

2) (

e2 fm4 )

94Mo, π = +

Jf = Ji + 2, 6602 transitions

Jf = Ji − 2, 7798 transitions

Ji = 2k to 10k, k = 1 to 40

Jf = Ji, Ji 1, 22196 transitions

all

+−

RITSSCHIL

R.S., PRC 90, 064321 (2014)

Page 35: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

E2 strength function in 74Ge

0 1 2 3 4 5 6Eγ (MeV)

0

1

2

3

4

5

B(E

2) (

e2 fm4 )

74Ge, π = +

Jf = Ji + 0,1,2; 36581 transitions

Jf = Ji − 2; 9002 transitions

Ji = 0k to 10k, k = 1 to 40

RITSSCHIL

Page 36: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

E2 strength function in 64Fe

0 1 2 3 4 5 6Eγ (MeV)

0

5

10

15

20

25

B(E

2) (

e2 fm4 )

64Fe, π = + ; ca48mh1

Jf = Ji + 0,1,2; 36593 transitions

Jf = Ji − 2; 9082 transitions

Ji = 0k to 10k, k = 1 to 40

B(E2, 2+

1 → 0+

1 )exp = 470+210−110 e2fm4

J. Ljungvall et al., PRC 81, 061301 (2010)

B(E2, 2+

1 → 0+

1 )calc = 406 e2fm4

NuShellX: B.A. Brown, W.D.M. Rae, NDS 120, 115 (2010)

Page 37: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Summary

Photon-scattering experiments on 74Ge with bremsstrahlung at γELBE using 7.5 and12.1 MeV electrons.

Determination of the dipole strength function at high excitation energy and high leveldensity. Inclusion of strength in the quasicontinuum and correction of the observedstrength for branching and feeding by using statistical methods.

No considerable enhancement of E1 strength in the pygmy region.

Good agreement between the strength functions deduced from the present (γ, γ′)

experiments and from (3He,3He’) experiments.

Low-energy enhancement observed in the (3He,3He’) experiment qualitatively de-scribed by M1 strength functions calculated within the shell model.Large M1 strengths result from a recoupling of the spins of specific high-j proton andneutron orbits.

E2 strength functions at low energy calculated within the shell model show simi-lar characteristics in various mass regions and are at variance with approximationsrecommended in RIPL.

Page 38: Ge 74 Gamma-ray strength functions in

Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de

Collaborators

Motivation: L.A. Bernstein (LLNL, Univ. Berkeley)

Data analysis: R. Massarczyk (HZDR, LANL)

Data acquisition: A. Wagner

Technical assistence: A. Hartmann

Experimenters: M. Anders, D. Bemmerer, R. Beyer, Z. Elekes, R. Hannaske,A.R. Junghans, T. Kogler, M. Roder, K. Schmidt, L. Wagner