Neutron resonance spectroscopy:Gd154,158,160

Abstract

Neutron time of flight spectroscopy measurements were made for a range of sample thickness on the even separated Gd isotopes $A=154, 158, \mathrm{and} 160$. These include transmission measurements using 200 and 40 m flight paths and self-indication measurements using a 40 m flight path. Resonance parameters were obtained for 48 levels to 1 keV for $^{154}\mathrm{Gd}$ and for 95 and 56 levels to 10 keV for $^{158}\mathrm{Gd}$ and $^{160}\mathrm{Gd}$. The experimental $s$-wave strength functions were $10^{4}S_{0}=(2.0\ifmmode\pm\else\textpm\fi{}0.3), (1.5\ifmmode\pm\else\textpm\fi{}0.2), \mathrm{and} (1.8\ifmmode\pm\else\textpm\fi{}0.4)$, respectively. For $^{160}\mathrm{Gd}$, the $p$ strength function is $10^{4}S_{1}\ensuremath{\approx}1.7\ifmmode\pm\else\textpm\fi{}0.3$. Essentially complete $s$-wave populations were obtained for the first 19 levels in $^{154}\mathrm{Gd}$ with $〈D〉=14.5\ifmmode\pm\else\textpm\fi{}1.5$ eV and ${\ensuremath{\Delta}}_{\mathrm{exp}}=0.22$ (vs ${\ensuremath{\Delta}}_{\mathrm{DM}}=0.28\ifmmode\pm\else\textpm\fi{}0.11$); 47 levels in $^{158}\mathrm{Gd}$ with $〈D〉=86\ifmmode\pm\else\textpm\fi{}4$ eV and ${\ensuremath{\Delta}}_{\mathrm{exp}}=0.29$ (vs ${\ensuremath{\Delta}}_{\mathrm{DM}}=0.38\ifmmode\pm\else\textpm\fi{}0.11$); and 20 levels in $^{160}\mathrm{Gd}$ with $〈D〉=202\ifmmode\pm\else\textpm\fi{}20$ and ${\ensuremath{\Delta}}_{\mathrm{exp}}=0.32$ (vs ${\ensuremath{\Delta}}_{\mathrm{DM}}=0.30\ifmmode\pm\else\textpm\fi{}0.11$). Comparison of the observed ${\ensuremath{\Gamma}}_{n}^{0}$ distributions with the Porter-Thomas theory and the observed level spacings with the Wigner theory and other statistical orthogonal ensemble tests gave good results for the energy intervals over which complete $s$ populations were observed. The average radiation widths were $〈{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}〉=88$ meV determined from $n=25$ levels in $^{154}\mathrm{Gd}$, $〈{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}〉=105$ meV ($n=27$) in $^{158}\mathrm{Gd}$ and $〈{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}〉=11$ meV ($n=4$) in $^{160}\mathrm{Gd}$.NUCLEAR REACTIONS $^{154,158,160}\mathrm{Gd}(n,n)$, ($n,\ensuremath{\gamma}$), $E=0\ensuremath{-}10$ keV; measured ${\ensuremath{\sigma}}_{t} (E)$; deduced ${E}_{0}$, ${\ensuremath{\Gamma}}_{n}$, ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$, ${S}_{0}$, $〈{D}_{0}〉$, ${S}_{1}$.