Parity dependence of the level densities ofCr53andCr55at high excitation

Abstract

The neutron total cross sections of $^{52}\mathrm{Cr}$ and $^{54}\mathrm{Cr}$ have been measured in the energy range from a few tens of keV to about 900 keV using a neutron time-of-flight technique and a pulsed electron linear accelerator. The nominal resolution of the measurements was about 0.06 ns/m. The total cross-section data have been analyzed using an $R$-matrix multilevel multichannel code to determine values of the resonance parameters (${E}_{0}$, $g{\ensuremath{\Gamma}}_{\mathrm{n}}$, and ${J}^{\ensuremath{\pi}}$) and to investigate the parity dependence of the level densities of $^{53}\mathrm{Cr}$ and $^{55}\mathrm{Cr}$ at high excitation. From these analyses we obtain the following values for the average properties of the resonance parameters for $s$-wave resonances up to about 900 keV and for $p$-wave resonances up to 600 keV: ${D}_{0}=(45\ifmmode\pm\else\textpm\fi{}6)$ keV, ${S}_{0}(\ifmmode\times\else\texttimes\fi{}{10}^{4})=(3.0\ifmmode\pm\else\textpm\fi{}1.0)$, ${D}_{1}=(8.5\ifmmode\pm\else\textpm\fi{}0.6)$ keV, ${S}_{1}(\ifmmode\times\else\texttimes\fi{}{10}^{4})=(0.70\ifmmode\pm\else\textpm\fi{}0.12)$ for $^{52}\mathrm{Cr}$; and ${D}_{0}=(60\ifmmode\pm\else\textpm\fi{}9)$ keV, ${S}_{0}(\ifmmode\times\else\texttimes\fi{}{10}^{4})=(2.6\ifmmode\pm\else\textpm\fi{}0.9)$, ${D}_{1}=(9.2\ifmmode\pm\else\textpm\fi{}0.5)$ keV, ${S}_{1}(\ifmmode\times\else\texttimes\fi{}{10}^{4})=(0.67\ifmmode\pm\else\textpm\fi{}0.11)$ for $^{54}\mathrm{Cr}$. The distributions of reduced neutron widths for $s$- and $p$-wave resonances for each isotope show good agreement with the Porter-Thomas distribution. The values of the ${\ensuremath{\Delta}}_{3}$ statistic for the long-range correlation of $s$-wave resonances for both $^{52}\mathrm{Cr}$ and $^{54}\mathrm{Cr}$ and found to be in reasonable agreement with the theoretical prediction of Dyson and Metha. The values for the ratio $\frac{{D}_{0}}{{D}_{1}}$ for both nuclides are larger than expected from a ($2J+1$) level dependence, indicative of a parity dependence of the level densities of $^{53}\mathrm{Cr}$ and $^{55}\mathrm{Cr}$ at high excitation.