Isomeric Cross-Section Ratios for Reactions Producing the Isomeric PairHg197,197m

Excitation functions and isomeric cross-section ratios were determined for the ${\mathrm{Au}}^{197}(p, n)$ and ${\mathrm{Au}}^{197}(d, 2n)$ reactions. Isomeric cross-section ratios were also determined for the ${\mathrm{Hg}}^{196}(n, \gamma )$, ${\mathrm{Hg}}^{196}(d, p)$, ${\mathrm{Hg}}^{198}(n, 2n)$, ${\mathrm{Hg}}^{198}(\alpha , \alpha n)$, and $\mathrm{Pt}(\alpha , xn)$ reactions. Those reactions for which compound nucleus formation predominates are treated by a statistical model. In this treatment the compound state is characterized by angular momentum and excitation energy. The analysis yields a value of 4±1 for the parameter $\sigma$ which characterizes the dependence of the nuclear level density on angular momentum. Relatively small amounts of angular momentum are transferred in reactions which proceed predominantly by a direct interaction mechanism. Such reactions, therefore, give a larger yield of the isomer with spin closer to that of the target nucleus.