L. E. Kirsch | Searcharxiv

arXiv2018

Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum

Statistical $γ$-decay from highly excited states is determined by the nuclear level density (NLD) and the $γ$-ray strength function ($γ$SF). These average quantities have been measured for several nuclei using the Oslo method. For the first time, we exploit the NLD and $γ$SF to evaluate the $γ$-width in the energy region below the neutron binding energy, often called the quasi-continuum region. The lifetimes of states in the quasi-continuum are important benchmarks for a theoretical description of nuclear structure and dynamics at high temperature. The lifetimes may also have impact on reaction rates for the rapid neutron-capture process, now demonstrated to take place in neutron star mergers.

nucl-ex↗

arXiv2017

RAINIER: A Simulation Tool for Distributions of Excited Nuclear States and Cascade Fluctuations

A new code has been developed named RAINIER that simulates the $γ$-ray decay of discrete and quasi-continuum nuclear levels for a user-specified range of energy, angular momentum, and parity including a realistic treatment of level spacing and transition width fluctuations. A similar program, DICEBOX, uses the Monte Carlo method to simulate level and width fluctuations but is restricted to $γ$-ray decay from no more than two initial states such as de-excitation following thermal neutron capture. On the other hand, modern reaction codes such as TALYS and EMPIRE populate a wide range of states in the residual nucleus prior to $γ$-ray decay, but do not go beyond the use of deterministic functions and therefore neglect cascade fluctuations. This combination of capabilities allows RAINIER to be used to determine quasi-continuum properties through comparison with experimental data. Several examples are given that demonstrate how cascade fluctuations influence experimental high-resolution $γ$-ray spectra from reactions that populate a wide range of initial states.

nucl-th↗