Photon Strength Functions and Spin Assignments in 95,96Mo from radiative neutron capture

Abstract

The $ˆ{94,95}$Mo(n,$gamma$) reaction was studied for neutron energies from thermal to 16 keV. The research was performed at the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos National Laboratory. The primary motivation for these measurements was to test an enhancement observed in the low energy behavior of the photon strength function in $ˆ{93-98}$Mo by the Olso Cyclotron group.

The gamma ray distribution and average gamma cascade multiplicity were measured following resonant neutron capture. These spectra were compared to simulations performed with the statistical model code DICEBOX. Results for a variety of photon strength function and level density models were simulated and compared to experiment. Models of the photon strength function with an Oslo-type enhancement below 1 MeV were unable to reproduce experimental spectra. However, good agreement was found between DANCE spectra and simulations that postulate a low-lying resonance in the photon strength function intermediate in strength between the KMF model and an Oslo-type photon strength function. A second experiment to measure the gamma ray spectra from thermal neutron capture at the Rez facility in Prague was performed with results consistent with the DANCE experiment.

New spin assignments were made for resonances in $ˆ{95,96}$Mo using the multiplicity of gamma ray cascades and the gamma ray spectral shape. In $ˆ{96}$Mo 56 resonances were observed with 17 resonances given a new spin assignment and 22 resonances given a tentative spin assignment. For $ˆ{95}$Mo a total of thirty nine resonances were observed with 21 given a parity assignment.