An isomeric state of platinum-199 has been produced by thermal-neutron irradiation of normal and enriched platinum samples. The isomer decays with a half-life of 14.1±0.3 seconds by the emission of $\gamma$ rays of 32±2 and 393±2 kev energy. The thermal-neutron activation cross section of ${\mathrm{Pt}}^{198}$ for the formation of the isomer is 0.028±0.003 barn. Tentative level assignments are made, consistent with systematics and shell theory.

• Received 12 February 1959

DOI:https://doi.org/10.1103/PhysRev.115.191