Radiations from Radioactive Indium (116)

The energy of the gamma-radiation emitted by indium (116) with the 54-minute period has been studied with a large hydrogen-filled cloud chamber. The indium was activated by slow neutrons from a cyclotron. The investigation used both the Compton recoil electrons from a carbon radiator of 35 mg/${\mathrm{cm}}^2$ surface density and the photoelectrons ejected from a lead sheet of 20 mg/${\mathrm{cm}}^2$ surface density. The recoil electrons from the carbon radiator indicate that the gamma-radiation is complex and that the spectrum can be resolved into three lines of 1.02, 1.40, and 1.85±0.05 Mev energy, the relative intensities of these lines being 1, 1, and ¼, respectively. The momentum distribution of the photoelectrons emitted from the lead radiator indicates that there are three low energy gamma-ray lines. These lines have energies of 0.17, 0.36, and 0.57±0.03 Mev and each has a relative intensity of about 1/7 compared with the 1.02-Mev line. The beta-ray spectrum of the 54-minute period has been investigated and the upper limit of the energy found to be 0.84±0.01 Mev. A measurement of the ratio of the beta-rays to the gamma-rays shows definitely that more than one quantum is emitted per electron. A level scheme is proposed which is in good agreement with all the data.