Electric dipole transitions from neutron capture inYb173resonances

Abstract

Primary neutron capture $\ensuremath{\gamma}$ rays have been studied from 49 neutron resonances in $^{173}\mathrm{Yb}$ in the 10-530 eV energy range. These resonances are assigned $J=2$ and $J=3$ on the basis of the intensity ratios of suitable pairs of low-energy $\ensuremath{\gamma}$ rays. The measured intensities of the high-energy primary $\ensuremath{\gamma}$ rays have been converted to partial radiation widths. These widths have been subjected to a correlation analysis against reduced neutron widths, with the result that convincing evidence was not found for previously reported nonstatistical behavior in this nucleus. The ratio of the average population of a particular low-lying level from $J=3$ resonances to its population from $J=2$ resonances was found to be in satisfactory agreement with a cascade model. Resonances in the 10-200 eV range were noted to exhibit an enhancement of $E1$ transition probabilities to $K=2$ final states as compared to $K=0$ states. A level scheme for $^{174}\mathrm{Yb}$ was constructed, and the neutron separation energy for this nucleus was deduced as 7464.5\ifmmode\pm\else\textpm\fi{}1.0 keV.NUCLEAR REACTIONS $^{173}\mathrm{Yb}$($n$,$\ensuremath{\gamma}$), $E=0.01\ensuremath{-}0.86$ keV; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$. $^{174}\mathrm{Yb}$ deduced resonances, $J$, deduced levels, partial radiation widths, correlations, neutron separation energy. Enriched target, Ge(Li) detector.