New Neutron-Deficient Isotopes of Rhenium

Abstract

Three new activities have been observed in rhenium obtained by bombardment of rhenium and of tungsten with protons of energies from 40 to 240 Mev and of enriched ${\mathrm{W}}^{180}$ with 10-Mev protons. Positron-emitting ${\mathrm{Re}}^{177}$ of 17-minute half-life was identified through its daughter, the known 2.2-hr ${\mathrm{W}}^{177}$. Evidence is presented for the assignment of ${\mathrm{Re}}^{178}$ to a 15-min, 3.1-Mev positron activity and of ${\mathrm{Re}}^{180}$ to a (20±1)-hour, 1.9-Mev positron activity. A previously reported unknown Re activity of approximately 1-hr half-life, which may possibly be an isomer of ${\mathrm{Re}}^{186}$, was also observed.