The Radioactive Isotopes of Indium

Abstract

It is shown that radioactive isotopes of indium may be formed possessing ten distinct half-lives ranging from 13 seconds to 50 days. By producing the various isotopes with different methods of excitation and measuring the energies of the beta- and gamma-radiations emitted by each, it now becomes possible to assign with reasonable certainty each radioactivity to an isotope of a particular mass number. Energy level diagrams can be constructed for certain of the excited nuclei. Increased resolution of the magnetic beta-ray spectrometer now makes it possible to identify positively the element in which internally converted gamma-rays are emitted. This is accomplished by observing the differences in the $K-$, $L-$ and $M$-conversion electron energies and comparing with known binding energies obtained from x-ray analysis. The total conversion coefficients are observed in several cases, and the ratios of $K$- to $L$-conversion coefficients for individual gamma-rays are used to compute the probable energy level spin values on the basis of present theory. A radioactivity of 50-day half-life assigned to ${\mathrm{In}}^{114}$ is shown to consist of a gamma-ray emission followed by a beta-ray of half-life 72 seconds and energy 1.98 Mev. It thus becomes possible to observe the form of this beta-spectrum in the magnetic spectrometer, and since it is an allowed transition it is significant to compare it with the present theory of beta-decay which has been developed only for transitions of this type and until now always tested by measurements on forbidden spectra. Within the probable errors the experimental results conform with the theoretical predictions of the Fermi theory.