Two New Promethium Isotopes; Cross Sections of Some Samarium Isotopes for 14.8-Mev Neutrons

When highly enriched samples of ${\mathrm{Sm}}^{152}$ and ${\mathrm{Sm}}^{154}$ are irradiated with 14.8-Mev neutrons, activities having half-lives of 6.5±0.5 min and 2.5±0.5 min are observed. On the basis of yields and cross-bombardments, these are assigned to new isotopes ${\mathrm{Pm}}^{152}$ and ${\mathrm{Pm}}^{154}$, respectively. Cross-section measurements at 14.8 Mev for ($n, 2n$), ($n, p$), and ($n, \alpha$) reactions of samarium are reported, the experimental values being as follows: ${\mathrm{Sm}}^{144}(n, 2n)$, 1200±300 mb; ${\mathrm{Sm}}^{154}(n, 2n)$, 1500±300 mb; ${\mathrm{Sm}}^{152}(n, p)$, 3.7±0.2 mb; ${\mathrm{Sm}}^{154}(n, p)$, 3.5±0.2 mb; ${\mathrm{Sm}}^{152}(n, \alpha )$, 10±2 mb; and ${\mathrm{Sm}}^{154}(n, \alpha )$, 9±3 mb. While the ($n, 2n$) cross sections are within an order-of-magnitude agreement with statistical evaporation theory, the experimental values for the ($n, p$) and ($n, \alpha$) cross sections are several orders of magnitude larger than those calculated from statistical evaporation theory based on the compound nucleus model.