Ge 74 Gamma-ray strength functions in

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Text optional: Institutsname Prof. Dr. Hans Mustermann www.fzd.de Mitglied der Leibniz-Gemeinschaft Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de Gamma-ray strength functions in 74 Ge 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 γ ELBE M1 and E2 strength at low energy: - Shell-model calculations

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Gamma-ray strength functions in 74Ge
Ronald Schwengner
01328 Dresden, Germany
- Photon-scattering experiments at γELBE
- Shell-model calculations
Study of germanium isotopes
Combination of experiments using neutron capture and alternative reaction techniques 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).
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
The bremsstrahlung facility at the electron accelerator ELBE
Accelerator parameters:
1 m
Be window
Detector setup at γELBE
Measurement at γELBE
1 2 3 4 5 6 7 8 9 10 11 Eγ (MeV)
10 5
10 6
10 7
10 8
10 9
C ou
nt s
pe r
10 k
o
Measurement at γELBE
1 2 3 4 5 6 7 8 9 10 11 Eγ (MeV)
10 5
10 6
10 7
10 8
10 9
C ou
nt s
pe r
10 k
o
Measurement at γELBE
1 2 3 4 5 6 7 8 9 10 11 Eγ (MeV)
10 5
10 6
10 7
10 8
10 9
C ou
nt s
pe r
10 k
o
Photon scattering - feeding and branching
0 Γ0
Iγ(Eγ, Θ) = Is(Ex) Φγ(Ex) (Eγ) Nat W (Θ)
Integrated scattering cross section:
Photon scattering - feeding and branching
0 Γ0
Iγ(Eγ, Θ) > Is(Ex) Φγ(Ex) (Eγ) Nat W (Θ)
Integrated scattering cross section:
Simulations of γ-ray cascades
PRC 87, 044306 (2013)
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
80, 054310 (2009).
S. I. Al-Quraishi et al., PRC 67, 015803 (2003).
Wigner level-spacing distributions.
Photon strength functions approximated by
Lorentz curves (www-nds.iaea.org/RIPL-2).
⇒ Subtraction of feeding intensities and correction
of intensities of g.s. transitions with calculated
branching ratios Γ0/Γ .
Average branching ratios of ground-state transitions in 74Ge
1 2 3 4 5 6 7 8 9 10 11 Ex (MeV)
0
20
40
60
80
100
Iterative determination of the absorption cross section
3 4 5 6 7 Ex (MeV)
0
1
2
3
0
5
10
Cross section including strength of resolved peaks and of quasi-continuum.
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Iterative determination of the absorption cross section
3 4 5 6 7 Ex (MeV)
0
1
2
3
0
5
10
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.
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Iterative determination of the absorption cross section
3 4 5 6 7 Ex (MeV)
0
1
2
3
0
5
10
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.
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Absorption cross section of 74Ge
3 4 5 6 7 8 9 10 11 Ex (MeV)
0
2
4
6
8
10
Absorption cross section of 74Ge
0 5 10 15 20 25 Ex (MeV)
10 0
10 1
10 2
Absorption cross section of 74Ge
0 5 10 15 20 25 Ex (MeV)
10 0
10 1
10 2
Absorption cross section of 74Ge
0 5 10 15 20 25 Ex (MeV)
10 0
10 1
10 2
A. Junghans et al.,
PLB 670, 200 (2008)
Electromagnetic strength functions
ffiL(Eγ) = ΓfiL ρ(Ei , Ji) / E 2L+1
γ Eγ = Ei − Ef Ji = 0, ..., Jmax
Photoabsorption:
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.
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Dipole strength functions in 74Ge
0 2 4 6 8 10 12 Eγ (MeV)
10 0
10 1
10 2
Dipole strength functions in 74Ge
0 2 4 6 8 10 12 Eγ (MeV)
10 0
10 1
10 2
(3He,3He’) data:
Dipole strength functions in 74Ge
0 2 4 6 8 10 12 Eγ (MeV)
10 0
10 1
10 2
TLO
Dipole strength functions in 74Ge
0 2 4 6 8 10 12 Eγ (MeV)
10 0
10 1
10 2
TLO GLO
(3He,3He’) data:
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Shell-model calculations of M1 strength functions
0 2 4 6 8 10 12 14 16 Eγ (MeV)
10 −2
10 −1
10 0
10 1
10 2
10 3
)γαHe, 3
)γ (p,p'
SM calc
Fe 56
) -3
( M
57 )γHe'
3 He,
)γ (p,p'
SM calc
RITSSCHIL NuShellX
PRL 111, 232504 (2013)
B.A. Brown, A.C. Larsen
PRL 113, 252502 (2014)
Generation of large M1 strengths
J + 1
⇒ Configurations including protons and neutrons in specific high-j orbits with large magnetic moments.
⇒ Coherent superposition of proton and neutron contributions for specific combinations of gπ and g ν factors and relative phases (“mixed symmetry”).
⇒ Large M1 strengths appear between states with equal configurations by a recoupling of the proton and neutron spins (analog to the “shears mechanism”).
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Dipole strength functions in 74Ge
0 2 4 6 8 10 12 Eγ (MeV)
10 −1
10 0
10 1
Dipole strength functions in 74Ge
0 2 4 6 8 10 12 Eγ (MeV)
10 −1
10 0
10 1
Dipole strength functions in 74Ge
0 2 4 6 8 10 12 Eγ (MeV)
10 −1
10 0
10 1
Predicted Appearance of magnetic rotation
0 20 40 60 80 100 120 140 16002040 6080100120140
Neutron Number N
qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . .. . . . . ................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................. ..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Generation of large M1 strengths
B(M1) ∼ µ 2
Examples near A = 80: 82Rb, 84Rb
H. Schnare et al., PRL 82, 4408 (1999).
R.S. et al., PRC 66, 024310 (2002).
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(0f4 5/2
5/2 )
⇒ Configurations including a broken ν0g9/2 pair in addition to π(fp) excitations.
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
E2 strength function in 94Mo
0 2 4 6 8 10 12 14 16 Eγ (MeV)
10 0
10 1
10 2
Lorentz curve with:
Γ = 6.11 – 0.021A MeV
−1/3 Γ −1 mb
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
E2 strength function in 94Mo
0 2 4 6 8 10 12 14 16 Eγ (MeV)
10 0
10 1
10 2
ρ(Ex , J) - level density
of the shell-model states,
RITSSCHIL
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
E2 strength function in 94Mo
0 1 2 3 4 5 6 Eγ (MeV)
0
5
10
Ji = 2k to 10k, k = 1 to 40
Jf = Ji, Ji 1, 22196 transitions
all
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
E2 strength function in 74Ge
0 1 2 3 4 5 6 Eγ (MeV)
0
1
2
3
4
5
Ji = 0k to 10k, k = 1 to 40

E2 strength function in 64Fe
0 1 2 3 4 5 6 Eγ (MeV)
0
5
10
15
20
25
Ji = 0k to 10k, k = 1 to 40

J. Ljungvall et al., PRC 81, 061301 (2010)
B(E2, 2+
1 → 0+
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Summary
Photon-scattering experiments on 74Ge with bremsstrahlung at γELBE using 7.5 and 12.1 MeV electrons.
Determination of the dipole strength function at high excitation energy and high level density. Inclusion of strength in the quasicontinuum and correction of the observed strength 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 and neutron 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 approximations recommended in RIPL.
Ronald Schwengner | Institut für Strahlenphysik | http://www.hzdr.de
Collaborators
Data acquisition: A. Wagner
Technical assistence: A. Hartmann