Program - Brookhaven National Laboratory

PC 2 4:00 PM
Theoretical Analysis of Gamma-ray Strength Function for Pd Isotopes
Nobuyuki Iwamoto
Nuclear Data Center, Japan Atomic Energy Agency, 2-4 Shirakata-shirane, Tokai, Ibaraki 319-1195,
Japan
Kazushi Terada
Department of Nuclear Engineering, Graduate School and Engineering, Tokyo Institute of Technology,
2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
The gamma-ray strength function (GSF) is one of the important elements to understand capture reaction
process by fast neutrons. The GSF is directly determined from measured data of photonuclear reaction.
However, information of the GSF below the neutron binding energy (BE) is not obtained from those
data. In order to fix the GSF below the BE, it is effective to use the measured spectrum of gamma-rays
emitted by neutron capture reaction, since the gamma-ray spectra are strongly affected by the GSF in the
energy region. In this work the evaluation of GSF was carried out by using gamma-ray spectra and cross
sections of neutron capture reactions for stable Pd isotopes and cross sections of photonuclear reaction for
natural Pd. The former data were recently measured with an anti-Compton NaI(Tl) spectrometer at Tokyo
Institute of Technology. Theoretical analysis was performed by applying CCONE code for nuclear reaction
calculation. As a result, we derived GSF which reproduced the both data simultaneously. The cross section
and gamma-ray spectrum for Pd-105 calculated on the basis of the GSF show a good agreement with the
recently measured data. The cross section decreases from that of JENDL-4.0 by 8% in the keV energy
region. This work was supported by JSPS KAKENHI Grant Number 22226016.
PC 3 4:20 PM
Statistical Properties of Nuclei by the Shell Model
Y. Alhassid
Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut
06520, U.S.A.
The shell model Monte Carlo (SMMC) approach provides a powerful method for calculating microscopically
the statistical properties of nuclei such as level densities in the presence of correlations. This method
enables us to carry out calculations in model spaces that are many orders of magnitude larger than
spaces that can be treated with conventional methods. We present a number of recent developments:
Heavy nuclei. We extended the SMMC approach to heavy nuclei using spaces of dimension ∼ 10 29 [1].
A conceptual challenge is whether a truncated spherical shell model can describe the proper collectivity
observed in such nuclei and in particular the rotational character of strongly deformed nuclei. We have
studied the crossover from vibrational (spherical) to rotational (deformed) nuclei in families of samarium
and neodymium isotopes [2]. Such a crossover can be identified by the temperature dependence of < J 2 >
where J is the total angular momentum. The latter observable and the state densities are found to be
in good agreement with experimental results. Collective enhancement factors. We have calculated the
collective enhancement factors of level densities versus excitation energy [2], and found that the decay
of vibrational and rotational enhancements is correlated with the pairing and shape phase transitions,
respectively. Odd-even and odd-odd nuclei. The projection on an odd number of particles leads to a sign
problem in SMMC. We developed a method to calculate the ground-state energy of a system with an odd
number of particles that circumvents this sign problem and applied it to calculate pairing gaps [3]. State
densities versus level densities. The SMMC approach has been used extensively to calculate state densities.
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