Dependence of theIn116Activation Ratio on Neutron Energy

Indium was irradiated with monochromatic neutrons of various energies, and a measurement was made of the ratio of the 54-minute to the 13-second activities of ${\mathrm{In}}^{116}$ produced by neutron capture in ${\mathrm{In}}^{115}$. Such a ratio expresses the relative probability for populating the ground or the isomeric state from the initial compound state. The irradiations were made with monochromatic neutrons from a crystal spectrometer at the resonance energies 1.456 ev and 3.86 ev, in regions between resonances at 0.1 and 2.66 ev, and with "pile neutrons." The results show that the activation ratio differs for the two resonances by a factor of approximately 3.5, with relatively more of the 13-second activity being associated with the 3.86-ev resonance. The half-lives of the two ${\mathrm{In}}^{116}$ activities were redetermined and the values 13.4±0.4 seconds and 53.9±0.2 minutes were obtained.