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Ronald Schwengner Institut für Strahlenphysik www.fzd.de Mitglied der Leibniz-Gemeinschaft
GAMMA-RAY STRENGTH-FUNCTION MEASUREMENTS AT ELBE
R. Schwengner1, G. Rusev1,2, N.Tsoneva3, N. Benouaret1,4, R. Beyer1, F.Donau1, M. Erhard1, S. Frauendorf1,5,
E. Grosse1,6, A. R. Junghans1, J. Klug1, K.Kosev1, H. Lenske3, C.Nair1, K.D. Schilling1, A.Wagner1
1 Institut fur Strahlenphysik, Forschungszentrum Dresden-Rossendorf, 01314 Dresden, Germany2 Dept. of Physics, Duke University and Triangle Universities Nuclear Laboratory, Durham, NC 27708
3 Institut fur Theoretische Physik, Universitat Gießen, 35392 Gießen, Germany4 Faculte de Physique, Universite des Sciences et de la Technologie d’Alger, 16111 Bab-Ezzouar, Algerie
5 Department of Physics, University of Notre Dame, Notre Dame, IN 465566 Institut fur Kern- und Teilchenphysik, Technische Universitat Dresden, 01062 Dresden, Germany
- The bremsstrahlung facility
- Photon-scattering experiments
- Data analysis and results
- QRPA and QPM calculations
- Photoactivation experiments
Supported by Deutsche Forschungsgemeinschaft
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Dipole strength close to the particle-separation energy
Understanding of astrophysicalprocesses:
– Influence on (γ,n) reactionrates in the p-process.
– Influence on (n,γ) reactionrates in the s-process.
Studies for transmutation:
– Analysis of (n,γ) reactions.
Open problems:
– Precise knowledge of the E1strength on the low-energy tailof the Giant Dipole Resonance.
– Properties of the E1 strengthfunctions at varying proton andneutron numbers: shell effects,deformation etc.
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
1000
σ (m
b)Sn
(γ,n)
88Sr
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Dipole strength close to the particle-separation energy
Understanding of astrophysicalprocesses:
– Influence on (γ,n) reactionrates in the p-process.
– Influence on (n,γ) reactionrates in the s-process.
Studies for transmutation:
– Analysis of (n,γ) reactions.
Open problems:
– Precise knowledge of the E1strength on the low-energy tailof the Giant Dipole Resonance.
– Properties of the E1 strengthfunctions at varying proton andneutron numbers: shell effects,deformation etc.
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
1000
σ (m
b)Sn
(γ,n)
88Sr
Lorentz E0 = 16.8 MeVΓ = 4.0 MeV
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Dipole strength close to the particle-separation energy
Understanding of astrophysicalprocesses:
– Influence on (γ,n) reactionrates in the p-process.
– Influence on (n,γ) reactionrates in the s-process.
Studies for transmutation:
– Analysis of (n,γ) reactions.
Open problems:
– Precise knowledge of the E1strength on the low-energy tailof the Giant Dipole Resonance.
– Properties of the E1 strengthfunctions at varying proton andneutron numbers: shell effects,deformation etc.
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
1000
σ (m
b)Sn
(γ,n)
88Sr
Lorentz E0 = 16.8 MeVΓ = 4.0 MeV
RIPL−2
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Dipole strength close to the particle-separation energy
Understanding of astrophysicalprocesses:
– Influence on (γ,n) reactionrates in the p-process.
– Influence on (n,γ) reactionrates in the s-process.
Studies for transmutation:
– Analysis of (n,γ) reactions.
Open problems:
– Precise knowledge of the E1strength on the low-energy tailof the Giant Dipole Resonance.
– Properties of the E1 strengthfunctions at varying proton andneutron numbers: shell effects,deformation etc.
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
1000
σ (m
b)Sn
(γ,n)
88Sr
Lorentz E0 = 16.8 MeVΓ = 4.0 MeV
RIPL−2
?
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
The radiation source ELBE
Electron Linear accelerator of high Brilliance and low Emittance
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
The bremsstrahlung facility at the electron accelerator ELBE
R.S. et al., NIM A 555 (2005) 211
Accelerator parameters:
• Maximum electron energy:
18 MeV
• Maximum average current:
1 mA
• Micro-pulse rate:
13 MHz
• Micro-pulse length:
≈ 5 ps1 m
Be-window
dipole
dipole
dipole
radiator
steerer
quadrupoles
quadrupole
electron-beam dump
quartz-windowbeam-
hardener
collimator
polarisationmonitor
target
PbPE
door
Pb
photon-beam dump
Pb
HPGe detector+ BGO shield
experimentalcave
acceleratorhall
clusterdetector
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Detector setup
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Nuclides under investigation in photon-scattering experiments
Z
42
40
38
36
34
48 50 52 54 56 58 N
nuclide Sn Ekine
MeV (MeV) ELBE
92Mo 12.7 6.0a, 13.2b,c,d
94Mo 9.7 13.2d
96Mo 9.2 13.2d
98Mo 8.6 (3.3, 3.8)a,e, (8.5, 13.2)b,c,d
100Mo 8.3 (3.2, 3.4, 3.8)a, (7.8, 13.2)b,c,d
90Zr 12.0 7.0, 9.0, 13.289Y 11.5 7.0f, 9.5, 13.288Sr 11.1 6.8g, (9.0, 13.2, 16.0)h
87Rb 9.9 4.0i, 13.286Kr 9.9 11.5
a G. Rusev et al., PRC 73 (2006) 044308b R. Schwengner et al., NPA 788 (2007) 331cc G. Rusev et al., PRC 77 (2008) 064321d A. Wagner et al., JPG 35 (2008) 014035e G. Rusev et al., PRL 95 (2005) 062501f J. Reif et al., NPA 620 (1997) 1g L. Kaubler et al., PRC 70 (2004) 064307h R. Schwengner et al., PRC 76 (2007) 034321i L. Kaubler et al., PRC 65 (2002) 054315
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Problem of 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
Scattering cross section integral:
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
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Problem of 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
Scattering cross section integral:
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
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absolute detector efficiency and photon flux
0 2000 4000 6000 8000 10000Eγ (keV)
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
ε (%
)
4000 6000 8000 10000 12000Eγ (keV)
0
20
40
60
80
100
120
140
160
180
200
Φγ (
(eV
s)−
1 )
Ee
kin = 13.2 MeV
Absolute efficiency of two detectors at 127 de-
duced from 22Na, 60Co, 133Ba, (filled circles) and
simulated with GEANT3 (solid line). Relative ef-
ficiencies deduced from 56Co (open circles), 11B
(open triangles) and 16O (open square).
Absolute photon flux deduced from transitions in11B using the calculated efficiency shown in the left
panel and relative photon flux calculated according
to G. Roche et al.
Code by E. Haug, Rad. Phys. Chem. 77 (2008) 207.
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Unresolved strength in the continuum
2 3 4 5 6 7 8 9 10 11 12 13 14Eγ (MeV)
100
101
102
103
104
105
Cou
nts
per
10 k
eV
90Zr
spectrum
backgroundatomic
3 4 5 6 7 8 9 10 11 12 13
Ex (MeV)
0
5
10
15
20
σ γγ ’ (
mb)
90Zr
peaks + cont.
peaks
∆=0.2 MeV
Experimental spectrum of 90Zr (corrected for room
background, detector response, efficiency, measur-
ing time) and simulated spectrum of atomic back-
ground.
Scattering cross sections in 90Zr averaged over en-
ergy bins of 0.2 MeV, not corrected for branch-
ing, derived from the difference of the experimen-
tal spectrum and the atomic background (triangles)
and from the resolved peaks only (circles).
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Problem of feeding and branching
Correction of the strength function by using statistical methods (G. Rusev, Dissertation):
⇒ Monte Carlo simulations of γ-ray cascades from groups of levels in 100 keV bins overthe whole energy range.
⇒ Level scheme of J = 0, 1 and 2 states constructed using: Backshifted Fermi-Gas Model with level-density parameters given in:
T. v. Egidy, D.Bucurescu, PRC 72 (2005) 044311
Wigner level-spacing distributions
⇒ Partial decay widths calculated by using: Photon strength functions approximated by Lorentzian parametrisations.– E1: parameters determined from a fit to (γ,n) data– M1: global parametrisation of M1 spin-flip resonances– E2: global parametrisation of E2 isoscalar resonances
(www-nds.iaea.org/RIPL-2)
Porter-Thomas distributions of decay widths.
⇒ Feeding intensities subtracted and intensities of g.s. transitions corrected with calculatedbranching ratios Γ0/Γ .
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Simulations of γ-ray cascades
0 2 4 6 8 10Eγ (MeV)
0.0
0.5
1.0
I γ (ar
b. u
nits
)
90Zr
Ground−statetransitions
Branching transitions
6 7 8 9 10 11 12Ex (MeV)
0
20
40
60
80
100
120
b 0∆ (%
)
90Zr
Simulated intensity distribution of transitions de-
populating levels in a 100 keV bin around 9 MeV.
⇒ Subtraction of intensities of branching transi-
tions.
Distribution of branching ratios b0 = Γ0/Γ versus
the excitation energy as obtained from the simula-
tions of γ-ray cascades for 90Zr.
⇒ Estimate of Γ0 and σγ.
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Test of simulated branching ratios
6 7 8 9 10 11 12Ex (MeV)
0
20
40
60
80
100
120
b 0∆ (%
)
90Zr
Measurement with monochromatic photons at
HIγS (∆E ≈ 200 keV).
Black: Population of 0+
2neglected.
Red: Assumption that b0+
2
= b2+
1
.
G. Rusev, A.P. Tonchev et al., priv. comm.
Distribution of branching ratios b0 = Γ0/Γ versus
the excitation energy as obtained from the simula-
tions of γ-ray cascades for 90Zr.
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Test of E1 strength functions
100
101
102
4 6 8 10 12 14 16100
101
102
100
101
102
Lorentzianδ = 0
σ γ (m
b)
Constant
σ γ (m
b)
Ex (MeV)
Lorentzianδ = 1
σ γ (m
b)
σγ(Ex) =2STRK
3π
3∑
i=1
E2x Γi(Ex)
(E 2
i− E 2
x )2 + E 2x Γ 2
i(Ex)
Γi(Ex) = ΓS · (Ex/Ei)δ; ΓS = 4 MeV;
f1 = σγ/[3(πhc)2Eγ]
STRK =
∫
∞
0
σγ(E ) dE = 60NZ
AMeV mb
Ei = hω0
(
1 −2
3ǫ2 cos
(
γ −
2πi
3
))
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
90Zr
(γ,γ’)uncorr
Present (γ, γ) data
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
(γ,γ’)corr
90Zr
(γ,γ’)uncorr
Present (γ, γ) data
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
(γ,γ’)corr
90Zr
(γ,p)
Present (γ, γ) data
(γ, p) calculated
ADNDT 88 (2004) 1
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
(γ,γ’)corr
90Zr
(γ,p) (γ,n)
Present (γ, γ) data
(γ, p) calculated
ADNDT 88 (2004) 1
(γ, n) data
PR 162 (1967) 1098
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
90Zr
Present (γ, γ) data
+ (γ, p) + (γ, n) data
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
90Zr
Present (γ, γ) data
+ (γ, p) + (γ, n) data
Lorentz curve:
E0 = 16.8 MeV
Γ = 4.0 MeVπ
2σ0Γ = 60 NZ
AMeV mb
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
90Zr
Present (γ, γ) data
+ (γ, p) + (γ, n) data
Lorentz curve:
E0 = 16.8 MeV
Γ = 4.0 MeVπ
2σ0Γ = 60 NZ
AMeV mb
RIPL-2(S. Goriely, E. Khan,NPA 706 (2002) 217)
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 90Zr
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
90Zr
Present (γ, γ) data
+ (γ, p) + (γ, n) data
Lorentz curve:
E0 = 16.8 MeV
Γ = 4.0 MeVπ
2σ0Γ = 60 NZ
AMeV mb
RIPL-2(S. Goriely, E. Khan,NPA 706 (2002) 217)
QRPA
Woods-Saxon basis
Γ = 3.2 MeV
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 88Sr
6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
88Sr
Present (γ, γ) data
+ (γ, n) data
Lorentz curve:
E0 = 16.8 MeV
Γ = 4.0 MeVπ
2σ0Γ = 60 NZ
AMeV mb
RIPL-2(S. Goriely, E. Khan,NPA 706 (2002) 217)
QRPA
Woods-Saxon basis:
Γ = 3.2 MeV
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross section in 89Y
5 6 7 8 9 10 11 12 13 14 15 16 17 18Ex (MeV)
1
10
100
σ γ (m
b)
Sn
89Y
Present (γ, γ) data
+ (γ, p) + (γ, n) data
Lorentz curve:
E0 = 16.8 MeV
Γ = 4.0 MeVπ
2σ0Γ = 60 NZ
AMeV mb
RIPL-2(S. Goriely, E. Khan,NPA 706 (2002) 217)
QRPA
Woods-Saxon basis:
Γ = 3.2 MeV
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
One-phonon QPM calculations for 88Sr and 90Zr
Transition densities of neutrons and protons:
0 5 10−0.15
−0.05
0.05
0.15
r2 ρ(r)
(fm
−1 )
−0.15
−0.05
0.05
0.15
0 5 10
r (fm)0 5 10
−0.5
0
0.5
−0.5
0
0.588Sr
90Zr
0
0
Ex < 9 MeV Ex = 9 − 9.5 MeV Ex = 9 − 22 MeVEnergy range below 9 MeV:
⇒ Oscillations at the surface
by neutrons only
⇒ Indication for a PDR
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross sections in Mo isotopes
σγ(Ex) =2STRK
3π
3∑
i=1
E2x Γi(Ex)
(E 2
i− E 2
x )2 + E 2x Γ 2
i(Ex)
Γi(Ex) = ΓS · (Ex/Ei)δ; ΓS = 4 MeV; δ ≈ 0
STRK =
∫
∞
0
σγ(E ) dE = 60NZ
AMeV mb
Ei = hω0
(
1 −2
3ǫ2 cos
(
γ −
2πi
3
))
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Absorption cross sections in Mo isotopes
σγ(Ex) =2STRK
3π
3∑
i=1
E2x Γi(Ex)
(E 2
i− E 2
x )2 + E 2x Γ 2
i(Ex)
Γi(Ex) = ΓS · (Ex/Ei)δ; ΓS = 4 MeV; δ ≈ 0
STRK =
∫
∞
0
σγ(E ) dE = 60NZ
AMeV mb
Ei = hω0
(
1 −2
3ǫ2 cos
(
γ −
2πi
3
))
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Comparison with other experiments
Present (γ, γ) data
(γ, n) data
H. Beil et al., NPA 227 (1974) 427
(3He,3He’γ) data
M. Guttormsen et al., PRC 71 (2005) 044307
(n, γ) data
J. Kopecky and M. Uhl, Bologna 1994
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
QRPA calculations for deformed nuclei
Hamiltonian for 1– states:
- Nilsson or Woods-Saxon mean field plus monopole pairing- isoscalar and isovector dipole-dipole and octupole-octupole interactionsF. Donau, PRL 94 (2005) 092503
F. Donau et al., PRC 76 (2007) 014317
Total energy as a function of the quadrupole deformation ε2 and the triaxiality γ:
0
10
20
30
40
50
60
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08ε2
γ
0
10
20
30
40
50
60
0.02 0.03 0.04 0.05 0.06 0.07 0.08ε2
γ
0
10
20
30
40
50
60
0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 0.14ε2
γ
0
10
20
30
40
50
60
0.16 0.18 0.2 0.22 0.24ε2
γ
0
10
20
30
40
50
60
0.16 0.18 0.2 0.22 0.24ε2
γ
92Mo5094Mo52
96Mo5498Mo56
100Mo58
ε2 = 0.0 ε2 = 0.02 ε2 = 0.10 ε2 = 0.18 ε2 = 0.21
γ = 60 γ = 37 γ = 32
TAC model with shell-correction method:
S. Frauendorf, NPA 557 (1993) 259c, NPA 667 (2000) 115
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
QRPA calculations in a deformed basis for Mo isotopes
0
4
8
12
16
20
0
4
8
12
16
4 5 6 7 8 9 10 11 12 130
4
8
12
16
92Mo 94Mo 96Mo 98Mo 100Mo
Experiment
/ TR
K (%
)
N
N
92Mo 94Mo 96Mo 98Mo 100Mo
QRPA with WS
/ TR
K (%
)
N
92Mo 94Mo 96Mo 98Mo 100Mo
Talys
/ TR
K (%
)
Ex (MeV)
Σ (Ex) =
Ex∑i
σγ(Ei) ∆E
ΣTRK =
∫∞
0
σγ(E ) dE = 60NZ
AMeV mb
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Summary
Study of dipole-strength distributions at high excitation energy and high level density viaphoton scattering.
Comparison of measured spectrum with calculated atomic background: 30 – 40% of thetotal dipole strength in resolved peaks and 70 – 60% in continuum.
Simulations of statistical γ cascades: Estimate of intensities of inelastic transitions.
Deduced σγ connect smoothly with (γ,n) data.
⇒ (i) Correct determination of σγ up to the (γ,n) threshold.(ii) Information on the photoabsorption cross section over the whole energy range fromlow excitation energy up to the GDR.(iii) Observation of extra strength in the range from 6 to 12 MeV – not described incurrent approximations of dipole-strength functions.
⇒ QPM calculations:(i) Qualitative description of the observed extra strength.(ii) Extra strength below 9 MeV caused by oscillations of the excessive neutrons.(iii) Increase of dipole strength below the neutron-threshold toward the heavier Moisotopes is correlated with increasing deformation.
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Photodissociation
Photodissociation reactions:
• (γ, n)
• (γ, p)
• (γ, α)
Method: photoactivation
• (A, Z ) + γ ⇒ (A, Z − 1 ) + p
• Measure decay rate of (A, Z − 1 )
Nact(Ee) = Ntar ·
∫Ee
Ethr
σ(γ,x) Φγ(E , Ee) dE
Nact(Ee) = Iγ(Eγ) · ε−1(Eγ) · p
−1(Eγ) · κcorr
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Photoactivation of92Mo
Electron capture (EC) and decay
9142Mo
−652.9 keV1/2
64.6 s
9/2+
15.5 min
0 keV
48.2%
9/2+
680 y
0 keV
−104.5 keV1/2
60.86 d
Nb4191
0.58%
Zr9140
1/2+0.17 ps
1204.8 keV
5/2+stable
0 keV
100% (2.9%) EC 93%
+β( <
0.2
%)
EC 2.9%
EC 4
%
A = 92A = 91Mo42
92
0+stable
0 keV
pS 7456 keV
12672 keVSn
9
3%
+β
+β 5
0%
not t
o sc
ale
Photoactivation process
γ+
transitions
β
Nact(Ee) = Ntar ·
∫Ee
Ethr
σ(γ,x) Φγ(E , Ee) dE
Nact(Ee) = Iγ(Eγ) · ε−1(Eγ) · p
−1(Eγ) · κcorr
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Setup for photoactivation experiments
caveBremsstrahlung
counting setupLow−levelAccelerator
hall
Photoactivationtarget
Electronbeam dump(rotated by 90°)
collimatorAluminium
targetactivationPhoto−
Leadwall
HPGedetectors
housingLead
beam dumpPhoton
PEblocks
castleLead
Photoactivatedtarget
detectorHPGe
Pneumatic delivery
Steel Iron
Electron beam
Graphite
Dewar
Depot
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Activation yield
Activation yields of Mo isotopes normalised to theactivation yield of the 197Au(γ, n) reaction.
Solid lines: NON-SMOKER,
T. Rauscher and F.-K. Thielemann,
ADNDT 88 (2004) 1
Dashed lines: TALYS,
A. Koning et al.,
AIP Conf. Proc. 769 (2005) 1154
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Activation yield
144Sm(γ,n)143Sm
144Sm(γ,n)143mSm
144Sm(γ, α)140Nd
Activation yields of 144Sm normalised to theactivation yield of the 197Au(γ, n) reaction.
Solid lines: NON-SMOKER,
T. Rauscher and F.-K. Thielemann,
ADNDT 88 (2004) 1
Dashed lines: TALYS,
A. Koning et al.,
AIP Conf. Proc. 769 (2005) 1154
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Activation yield – low-background measurement
Spectra of the decay of140Nd →
140Pr → 140Cefollowing the144Sm(γ, α) reaction.
Measured in ELBE building
Measured in underground lab“Felsenkeller” in Dresden
Ronald Schwengner Institut für Strahlenphysik Forschungszentrum Dresden-Rossendorf www.fzd.de
Summary
Photodissociation of Mo isotopes and of 144Sm studied via photoactivation at the ELBEaccelerator.
Determination of the photon flux in the electron-beam dump by means of the197Au(γ, n) reaction.
Measurement of weak decay rates in an underground lab.
92Mo(γ, α)88Zr and 144Sm(γ, α)140Nd reactions observed for the first time at astrophys-ically relevant energies.
Rough agreement with predictions of Hauser-Feshbach models for (γ, n) and (γ, p) re-actions. Predictions differ for (γ, α) reactions.
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