High-Spin IsomerIr194m2Produced by Triple Neutron Capture

Abstract

A 171-day high-spin ($I>~10$) isomer was discovered in ${\mathrm{Ir}}^{194}$. It is predominantly formed by three successive neutron captures from ${\mathrm{Ir}}^{191}$, via successively higher spin states in ${\mathrm{Ir}}^{192}$ ($I=4\mathrm{}$) and ${\mathrm{Ir}}^{193m}$ ($I=\frac{11}{2}$). The isomer decays by $\gamma$ decay chiefly to a 2438-keV state in ${\mathrm{Pt}}^{194}$, which is depopulated by two parallel branches. The more intense branch proceeds through a "ground-state band" ($8^{+}$→$6^{+}$→$4^{+}$→$2^{+}$→$0^{+}$) whose level energies indicate that ${\mathrm{Pt}}^{194}$ is a somewhat deformed and very "soft" nucleus.