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 ${\mathrm{Ir}}^{192}$ ($I=4$) and ${\mathrm{Ir}}^{193m}$ ($I=\frac{11}{2}$). The isomer decays by $\ensuremath{\gamma}$ 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" (${8}^{+}$\ensuremath{\rightarrow}${6}^{+}$\ensuremath{\rightarrow}${4}^{+}$\ensuremath{\rightarrow}${2}^{+}$\ensuremath{\rightarrow}${0}^{+}$) whose level energies indicate that ${\mathrm{Pt}}^{194}$ is a somewhat deformed and very "soft" nucleus.