Study of gamma decay in 168Er from neutron capture

The γ-ray emission process in highly-excited nuclei is typically described within the statistical model of nucleus using the two main ingredients - the level density (LD) and the photon strength functions (PSFs). The knowledge of LD and PSFs is essential in the modeling of nuclear reactions with applications in astrophysics or advanced nuclear reac- tors. In this work, we studied the multi-step γ-ray cascade spectra following the radiative neutron capture 167 Er(n, γ)168 Er measured with the Detector for Advanced Neutron Cap- ture Experiments in Los Alamos National Laboratory. The experimental γ-ray spectra were compared with the simulated spectra exploiting the dicebox Monte Carlo code for simulation of radiative decay to test different models of LD and PSFs. Furthermore, the measured spectra allowed us to determine the population of the isomeric state in 168 Er with 109 ns half-life and compare it with the simulated isomeric population, which provides an important test of the applicability of the statistical model. The simulated isomeric population was found to be significantly lower than the experi- mental one if no structure effects are assumed above the excitation energy of the isomer. If we adopt the decay scheme up to excitation energy well above 2 MeV, we obtain the simulated isomeric ratio..