Induced Radioactivity in Strontium and Yttrium; Nuclear Isomers in Strontium

Abstract

In revising and extending previous work on induced radioactivity in strontium and yttrium, it was found that with stronger activation by deuterons and neutrons, more accurate determinations could be made of the radioactive decay periods, and measurements of beta- and gamma-ray energies could be made with greater certainty. Periods of 2.0±0.2 hours, 14±2 hours, and 82±4 hours were found in yttrium separated from strontium bombarded with 7-Mev deuterons. The first of these periods was assigned to ${\mathrm{Y}}^{88}$, and the other two either to ${\mathrm{Y}}^{85}$ and ${\mathrm{Y}}^{87}$, or to isomeric forms of either of these. Periods of 3.0±0.1 hours and 55±5 days, produced in strontium by bombardment of that element with deuterons and neutrons, were assigned to the decay of isomeric forms of ${\mathrm{Sr}}^{89}$, and the nature of that isomerism was investigated. From measurements in the cloud chamber, the maximum energy of the beta-rays from the 3-hour isomer was found to be 0.60 Mev, those from the 55-day isomer had an upper limit of 1.50 Mev, and the gamma-radiation which accompanied the 3-hour decay was found to have two components, of 0.55 Mev and 1.10 Mev. A tentative energy level diagram suggests that the metastable state of ${\mathrm{Sr}}^{89}$ decays first by the emission of a beta-particle and then by the emission of either one or two gamma-rays. The ground state of ${\mathrm{Sr}}^{89}$ decays directly to the ground state of ${\mathrm{Y}}^{89}$ without the emission of gamma-radiation.