gamma-ray strength functions obtained with the oslo method ann-cecilie larsen july 8, 2008 workshop...
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Gamma-ray strength functions obtained with the Oslo method
Ann-Cecilie Larsen
July 8, 2008
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
DEPARTMENT OF PHYSICSUNIVERSITY OF OSLO
Collaborators
Oslo: A. Bürger, M. Guttormsen, S. Messelt, F. Ingebretsen, H. T. Nyhus, J. Rekstad, S. Siem,
N.U.H. Syed, and H. K. Toft Livermore National Lab.: U. Agvaanluvsan,
L. Bernstein North Carolina State University/TUNL:
R. Chankova, G. E. Mitchell Åbo Akademi University, Finland: T. Lönnroth Ohio University: A. Schiller A. Voinov
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Outline
Introduction & motivation Oslo experiments Gamma-ray strength functions, medium-
mass nuclei Gamma-ray strength functions, 116,117Sn Summary & outlook
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Decay probability
Fermi’s Golden Rule: Statistical decay: Gamma-ray strength function:
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
i
f
€
λ=2π
hf ˆ H i
2
ρ(E f )
€
λ∝ρ(E f ) ⋅T(Eγ )
€
fXL =TXL (Eγ ) /(2π Eγ2L +1)
Resonances
Giant electric dipole resonance M1 spin-flip, E2 isoscalar M1 scissors mode, E1 skin oscillation
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
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117Sn(,xn)Lepretre et alNPA 219, 39(1974).
Experiments at OCL
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Selected reactions: (3He,3He’), (3He,), (p,p’), (p,t) ... Low spin and high intrinsic excitation energy CACTUS: 28 5”x5” NaI (~15% eff.) Eight E-E Si particle telescopes
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Particle - gamma coincidences
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Si E-E telescope
45o
NaI(Tl)
3He
Target nucleus
Coincidence matrices
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
44Sc, unfolded 44Sc, first-generation -rays
Sn
Sp
Extraction of level density and gamma-ray transmission coeff.
The first-gen. -ray matrix P(E,E)is factorized according to
P(E,E) ρ(E-E)T(E)
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Theoretical vs. experimental first-gen. spectra
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
50V 44Sc
Normalization
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Level density: a) Low E: discrete levelsb) At Sn: neutron res. spacing Slope and abs. magnitude
Gamma-ray transm. coeff.: Total, average radiative width at Sn
Gamma-ray strength functions, medium-mass nuclei
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
TXL(E) = 2 E2L+1 fXL
From transmissioncoefficient to -ray strength function:
fXL = TXL(E) / (2 E
2L+1)
Assuming dipole radiationis dominant:
fE1+M1 = Texp(E) / (2 E3)
Comparison with models and photoabsorption data, 44Sc
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Photoabs. cross section to strength function:
E1 strength, Kadmenski, Markushev and Furman model:
M1 spin flip and E2 isoscalar (Lorentzians)
Is the up-bend structure dependent on excitation energy?
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
45Sc, first.gen. matrix
Gamma-ray strength functions, 116,117Sn
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Comparison with models and microscopic calculations, 116,117Sn
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Comparison with photoneutron cross-section data, 116,117Sn
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Dependence on excitation energy?
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
116Sn, first.gen. matrix
E1 pygmy resonance, unstable Sn isotopes
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
LAND group, GSIMeasuring above the neutron separation energy
Adrich et al., PRL 95, 132501 (2005)130Sn: 7(3)% of TRK sum rule132Sn: 4(3)% of TRK sum rule
E1 pygmy resonance, stable Sn isotopes
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Nuclear resonance fluorescence (,’)Govaert et al., PRC 57, p. 2229 (1998)116Sn: B(E1) = 0.204(25) e2 fm2
124Sn: B(E1) = 0.345(43) e2 fm2
≈ 0.4–0.6% of TRK sum rule
Oslo measurements:116,117Sn: 16(7) MeV mb (QRPA)
17(7) MeV mb (GLO) ≈ 1.0(4)% of TRK sum rule
Summary & outlook
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Oslo experiments – level density & -ray strength function
Medium-mass nuclei: Enhanced strength at low -ray energies
116,117Sn: functional form of a “pygmy” resonance Future experiments: 90,92Zr, U, Th, Pd... Upgrade of exp. setup: Silicon Ring (SiRi) particle
detection system NaI LaBr3(Ce)?
Preliminary data, 46Ti
Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio
Level density Gamma-ray strength function