Extraction of the Nuclear Level Density ⁶⁸Cu and ⁶⁵Ni using LANSCE/WNR neutron beams and the evaporation technique

Nuclear reactions involved in stellar evolution generally occur at energies much lower than the Coulomb barrier, making neutron induced reactions vital in the synthesis of chemical elements, particularly those heavier than iron. Reactions of the (n,a) and (n,p) types can be utilized to extract nuclear level densities (NLD) of unstable isotopes, essential for accurate reaction rate calculations, using the evaporation technique. To probe nuclear level densities in the Ni region, cross sections measurements for ⁶⁸Zn(n,p)⁶⁸Cu and ⁶⁸Zn(n,a)⁶⁵Ni were carried out at WNR facility at LANSCE using the Low Energy (n,z) (LENZ) detection system.

The main idea of the evaporation technique is that the differential cross section for the emission of a particle from a compound nucleus is proportional to the appropriate transmission coefficient and NLD. Therefore, the detailed shape of the particle spectrum is determined by the energy dependence of the level density. Further improvement of the experimental level density can be achieved by comparing the experimental spectra to those calculated with the Hauser-Feshbach theory and adjusting the theory parameters to reproduce the experimental spectra. In this talk, we present details on the experimental setup, analysis, and preliminary results for the measurement of ⁶⁸Zn(n,a)⁶⁵Ni and ⁶⁸Zn(n,p)⁶⁸Cu reaction cross section and the extraction of the nuclear level density of ⁶⁸Cu and ⁶⁵Ni.