Neutron Resonances of Mo Isotopes

Abstract

The neutron transmission of Mo isotopes for neutron energy ${E}_{n}\ensuremath{\lesssim}1.5$ keV has been measured with the Argonne fast chopper. The use of samples enriched in ${\mathrm{Mo}}^{95}$ and in ${\mathrm{Mo}}^{97}$ as well as samples of natural Mo has made possible the unambiguous isotopic assignment of the resonances. Some ten new resonances have been detected and measured; all of these have been assigned to either ${\mathrm{Mo}}^{95}$ or ${\mathrm{Mo}}^{97}$. On the basis of a probability approach recently suggested by Bollinger, a great majority of these newly observed resonances have been interpreted as being due to $p$-wave neutrons. For ${\mathrm{Mo}}^{95}$ the mean radiation width calculated from the measurements for the resonances at ${E}_{0}=44.7 \mathrm{and} 159.6$ eV is ${〈{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}〉}_{l=0}=185\ifmmode\pm\else\textpm\fi{}15$ meV. This is to be compared with ${〈{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}〉}_{l=1}=277\ifmmode\pm\else\textpm\fi{}67$ meV for the two $p$-wave resonances at ${E}_{0}=110.3 \mathrm{and} 117.9$ eV. For ${\mathrm{Mo}}^{96}$, the widths are ${〈{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}〉}_{l=0}=330\ifmmode\pm\else\textpm\fi{}50$ meV for the resonance at 131.3 eV, and ${({\ensuremath{\Gamma}}_{\ensuremath{\gamma}})}_{l=1}=530\ifmmode\pm\else\textpm\fi{}100$ meV for the resonance at ${E}_{0}=113.5$ eV. For ${\mathrm{Mo}}^{97}$, the radiation widths are ${({\ensuremath{\Gamma}}_{\ensuremath{\gamma}})}_{l=0}=127\ifmmode\pm\else\textpm\fi{}13$ meV for the $s$-wave resonance at ${E}_{0}=70.9$ eV, and ${〈{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}〉}_{l=1}=154\ifmmode\pm\else\textpm\fi{}20$ meV for four of the $p$-wave resonances detected in this experiment. The values for ${\mathrm{Mo}}^{98}$ are ${({\ensuremath{\Gamma}}_{\ensuremath{\gamma}})}_{l=0}=170\ifmmode\pm\else\textpm\fi{}80$ meV for the $s$-wave resonance at ${E}_{0}=428.9$ eV, and ${({\ensuremath{\Gamma}}_{\ensuremath{\gamma}})}_{l=1}=110\ifmmode\pm\else\textpm\fi{}15$ meV for the $p$-wave resonance at ${E}_{0}=12.1$ eV. The strength functions calculated for these nuclides are ${S}_{0}({\mathrm{Mo}}^{95})=({{0.5}_{\ensuremath{-}0.2}}^{+0.5})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, ${S}_{1}({\mathrm{Mo}}^{95})=({{5}_{\ensuremath{-}3}}^{+10})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$; ${S}_{0}({\mathrm{Mo}}^{97})=({{0.5}_{\ensuremath{-}0.2}}^{+0.4})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, ${S}_{1}({\mathrm{Mo}}^{97})=({{6}_{\ensuremath{-}2}}^{+11})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$; and ${S}_{0}({\mathrm{Mo}}^{98})=({{2}_{\ensuremath{-}1}}^{+4})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. The resonance-capture integral for natural Mo has been calculated to be 27\ifmmode\pm\else\textpm\fi{}2 b.