M3Isomeric Transition in Tin-113

The isomeric state of ${\mathrm{Sn}}^{113}$ has been produced by thermal neutron irradiation of tin enriched in ${\mathrm{Sn}}^{112}$. Its half-life is found to be (20±1) min. The scintillation spectrum shows $K$ x rays and a single gamma ray of 79±3 kev. The $K$-conversion coefficient (${\epsilon }_K=95\mathrm{}\pm 15$) and the half-life show that this isomeric transition is $M3\mathrm{}$, and not $M4\mathrm{}$, as has been reported. A (9±2)% electron capture branch from the isomeric state was found, and an upper limit of ${10}^{-4\mathrm{}}$ was placed on the ratio of positron emission to electron capture. The latter value limits the decay energy to the ground state of ${\mathrm{In}}^{113}$ to ≤1.15 Mev. Spins and parities of $\frac{7}{2}+$ for ${\mathrm{Sn}}^{113m}$ (20 min) and ½+ for ${\mathrm{Sn}}^{113g}$ (118 day) are assigned. The isomeric ratio $\frac{\sigma \left({\mathrm{Sn}}^{113m}\right)}{\sigma \left({\mathrm{Sn}}^{113g}\right)}$ was found to be (0.41±0.06), and a value of (0.35±0.08) barn was obtained for the production cross section of the isomer.