Parity nonconservation in106Pdand108Pdneutron resonances

Abstract

Parity nonconservation (PNC) has been studied in the neutron p-wave resonances of ${}^{106}\mathrm{Pd}$ and ${}^{108}\mathrm{Pd}$ in the energy range of 20 to 2000 eV. Longitudinal asymmetries in p-wave capture cross sections are measured using longitudinally polarized neutrons incident on $\ensuremath{\sim}20\ensuremath{-}\mathrm{g}$ metal-powder targets at LANSCE. A CsI $\ensuremath{\gamma}$-ray detector array measures capture cross section asymmetries as a function of neutron energy which is determined by the neutron time-of-flight method. A total of 21 p-wave resonances in ${}^{106}\mathrm{Pd}$ and 21 p-wave resonances in ${}^{108}\mathrm{Pd}$ were studied. One statistically significant PNC effect was observed in ${}^{106}\mathrm{Pd},$ and no effects were observed in ${}^{108}\mathrm{Pd}.$ For ${}^{106}\mathrm{Pd}$ a weak spreading width of ${\ensuremath{\Gamma}}_{w}{=34}_{\ensuremath{-}28}^{+47}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7} \mathrm{eV}$ was obtained. For ${}^{108}\mathrm{Pd}$ an upper limit on the weak spreading width of ${\ensuremath{\Gamma}}_{w}<12\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7} \mathrm{eV}$ was determined at the 68% confidence level.