Level densities and radiative strength functions

Journal Article · Wed Jan 28 04:00:00 EST 2009 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3087125· OSTI ID:21255519

Siem, S; Buerger, A; Guttormsen, M; Larsen, A C; Nyhus, H T; Rekstad, J; Syed, N U. H.; Toft, H K; Tveten, G M ^[1]; Agvaanluvsan, U ^[2]; Mitchell, G; Chankova, R ^[3]; Schiller, A; Voinov, A ^[4]

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1. Department of Physics, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo (Norway)
2. Lawrence Livermore National Laboratory, L-414, 7000 East Avenue, Livermore, CA 94551 (United States)
3. Department of Physics, North Carolina State University, Raleigh, NC 27695 (United States)
4. Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 (United States)

This paper presents a summary of the latest results from experiments performed at the Oslo Cyclotron. The Oslo group has developed a technique to extract simultaneously the level density and radiative strength function from primary {gamma}-ray spectra. A small (pygmy) resonance in the radiative strength function has been observed at around 3 MeV in several deformed rare earth nuclei. This resonance is shown to be of M1 character and the origin is thought to be the scissors mode. This resonance vanishes for the spherical Sm nuclei, as expected, since the scissors mode is dependent on deformation. Experiments performed in Oslo found the resonance in Dy isotopes to be twice as wide as the width extracted in an indirect way by comparing simulations with two-step cascade spectra from neutron capture experiments. In {sup 116,117}Sn an increase in the slope of the radiative strength function around E{sub {gamma}} = 4.5 MeV indicates the onset of resonance-like structures in both nuclei, resulting in a significant enhancement of the radiative strength functions compared to standard models in the energy region 4.5<E{sub {gamma}}<7.7 MeV. Another interesting phenomenon is the unexpected enhancement of the {gamma}-strength function below 4 MeV which has been observed in Fe, Mo, V, and Sc isotopes. The level density and radiative strength function of {sup 96}Mo have been reanalyzed, and the enhanced {gamma} strength for E{sub {gamma}}<3-4 MeV is confirmed. This enhancement is presently not understood and remains a challenge for theoretical models.

• OSTI ID: 21255519
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 1090; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
DYSPROSIUM ISOTOPES
ENERGY-LEVEL DENSITY
GAMMA SPECTRA
IRON ISOTOPES
MEV RANGE 01-10
MOLYBDENUM 96
NEUTRON REACTIONS
OSLO CYCLOTRON
RADIANT HEAT TRANSFER
RARE EARTH NUCLEI
SCANDIUM ISOTOPES
STRENGTH FUNCTIONS
TIN 116
TIN 117
VANADIUM ISOTOPES