Radioactivity ofIn120andSb120

An investigation of the radiations from the mass-120 isobars has been made using magnetic lens, scintillation pulse-height, and coincidence counting techniques. ${\mathrm{Sb}}^{120m}$ decays with a 5.8-day half-life by electron capture, positron emission if any ${\mathrm{Sn}}^{120}$ which then decays by the emission of the following gamma rays (energies in Mev): 0.089 ($E1\mathrm{}$), 0.199 ($E2\mathrm{}$), 1.04 ($E2\mathrm{}$), and 1.18 ($E2\mathrm{}$). The 1.18-Mev gamma ray also occurs in the decay of the 16-min ${\mathrm{Sb}}^{120}$, where the number of gamma rays per positron is 0.03. An activity of ∼55 sec is assigned to ${\mathrm{In}}^{120m}$. A decay scheme is proposed.