Isomerism ofIn110andIn112

The decay of ${\mathrm{In}}^{110}$ and ${\mathrm{In}}^{112}$ has been investigated with the aid of beta-ray spectrometer and coincidence measurements. From the half-life 20.7±0.3 min and the $\frac{K}{\mathrm{}(L+M)\mathrm{}}$ ratio 3.7±0.4, the 155±1-kev isomeric transition in ${\mathrm{In}}^{112}$ is identified as $M3\mathrm{}$. The 14.5±1-min ground state emits an allowed negatron spectrum of 656±6 kev and an allowed positron spectrum of 1.52±0.05 Mev. Even parity and spins of 4 and 1 are assigned to the two states. The 66-min ground state of ${\mathrm{In}}^{110}$ decays by emission of an allowed positron spectrum of 2.25±0.02 Mev to the 657-kev level of ${\mathrm{Cd}}^{110}$. The electron capture from the $4.9\pm 0.2-h$ isomeric state is followed by the known 884, 937, and 657-kev gamma-rays in ${\mathrm{Cd}}^{110}$. Even parity is assigned to both levels. Conversion lines, with $\frac{K}{\mathrm{}(L+M)\mathrm{}}=4.5\mathrm{}\pm 1$ indicate an additional gamma-ray of 121 kev which may be the isomeric transition having a branching ratio of about 0.6 percent. It would have to be an $M3\mathrm{}$ transition with an abnormally long (factor ${10}^3$) half-life. The existence of the ${\mathrm{In}}^{110}$ isomer is shown to remove several difficulties in the interpretation of the excitation curves of the alpha-particle reactions with silver.