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Although there are but two stable isotopes of indium whose mass numbers are 113 and 115, seven radioactive periods are shown to exist. Six of these whose half-life periods are 13 seconds, 72 seconds, 54 minutes, 2.3 hours, 4.1 hours and 50 days emit negative electrons, and one period of 20 minutes is radiopositive. By bombarding indium with slow neutrons, deuterons and very fast neutrons, and by bombarding cadmium with deuterons it is possible to assign with considerable confidence each period to a certain indium isotope. The conclusions are that the 54 minute and 13 second activities are both due to In 116 , the 4.1-hour and 50-day periods are both In 114 and the 20-minute, 72-second and 2.3-hour periods are from isotopes of mass 111, 112, and 117, respectively. Beta-ray energy limits are approximately 2.15 Mev for the 50-day period and 1.75 Mev for the 20-minute positive period.

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The beta-ray spectra of phosphorus, sodium and cobalt have been obtained by means of a magnetic spectrometer of high resolving power. In the cases of phosphorus and sodium, where the most accurate work was possible, the shapes of the spectra differ from the results previously reported by other investigators in that there are fewer low energy particles. The reduction in this number of particles has been traced to the relative absence of scattering in the radioactive source and its mounting. The general shape of the spectra is found to agree more satisfactorily with that predicted from the original theory of Fermi than that given by the modification of this theory proposed by Konopinski and Uhlenbeck. The maximum energy of the continuous electrons emitted from phosphorus and sodium are found to be 1.72 and 1.4 Mev, respectively. The value for sodium electrons is considerably lower than has been previously observed. The shape of the cobalt positron spectrum suggests two superimposed continuous distributions. The observed upper energy limit of 1.50 Mev agrees fairly well with the previously reported value. The excellent resolution of the spectrometer is illustrated by the separation of the K and L shell conversion electrons arising from a gamma-ray in indium. The observed resolution is only slightly less than the calculated value due to the absorption of electrons in the source.