Gamma Rays from Inelastic Neutron Scattering in Chromium

Abstract

Gamma-ray spectra from the $\mathrm{Cr}(n, n^{\prime }\gamma )$ reaction have been studied using a ring geometry for ten ${\mathrm{Li}}^7(p, n)$ neutron energies ranging from 0.98 to 3.31 MeV. Isotopic assignments have been made for the observed gamma rays, and differential gamma-ray production cross sections have been obtained at $\overline{\theta }=100\mathrm{}°$. In order to convert these to inelastic neutron cross sections, calculations using Satchler's theory have been carried out for the angular distributions of the pertinent gamma-ray transitions in ${\mathrm{Cr}}^{50}$, ${\mathrm{Cr}}^{52}$, and ${\mathrm{Cr}}^{54}$. The resulting experimental ($n, n^{\prime }$) cross sections for individual levels have been compared to predictions using Hauser-Feshbach theory and various diffuse surface potentials. The use of the ($n, n^{\prime }\gamma$) reaction as a nuclear spectroscopic tool has proved to be of value, since new information has been found concerning the properties of some of the low-lying states of ${\mathrm{Cr}}^{52}$ and ${\mathrm{Cr}}^{53}$. The relationship of these new results to other available experimental evidence and to current theoretical predictions is discussed in detail, particularly the possibility of appreciable fragmentation of the $2p_{\frac{3}{2}}$ and $2p_{\frac{1}{2}}$ single-particle states in ${\mathrm{Cr}}^{53}$. The evidence for contributions of core excitation to ${\mathrm{Cr}}^{53}$ states is also considered. Finally, comparison of the total inelastic neutron cross section for Cr and each of its four stable isotopes has been made with theoretical predictions.