Decay of Neutron-Deficient Isotopes of Pd and Rh

Abstract

Pd isotopes of masses 98, 99, and 101 were prepared by $\alpha$-particle bombardment of ruthenium. The radiations of these isotopes and of their Rh daughters were investigated with a scintillation coincidence spectrometer. ${\mathrm{Rh}}^{98}$ decays with a half-life of 8.7±0.1 minutes by emission of 2.5±0.2 Mev positrons in coincidence with 650±10 kev $\gamma$ rays. Its ${\mathrm{Pd}}^{98}$ parent was shown by successive daughter extractions to decay with a half-life of 17.5±0.5 minutes. ${\mathrm{Rh}}^{99}$ (4.7±0.1 hours) showed 0.74-Mev positrons (10%) in coincidence with 335±10 kev $\gamma$ rays (70%). Other $\gamma$ rays were observed at 615±15 kev (20%), 890±20 kev (weak line coincident with 335-kev $\gamma$), 1.26±0.03 Mev, and 1.41±0.04 Mev (weak). ${\mathrm{Pd}}^{99}$ (21.6±0.6 minutes) was identified by successive Rh daughter extractions. Its maximum positron energy is 2.0±0.1 Mev and the following $\gamma$ rays were observed: 140, 275, 420, and 670 kev. The 140-kev $\gamma$ ray is the most intense and the 420-kev peak represents two $\gamma$ rays of about the same energy in cascade. ${\mathrm{Rh}}^{101}$ (4.7±0.2 days) decays by electron capture followed by emission of 312±10 kev $\gamma$ rays. ${\mathrm{Pd}}^{101}$ (8.5±0.3 hours) emits 0.58±0.04 Mev positrons (4%) by decay to the ground state of ${\mathrm{Rh}}^{101}$. The $\gamma$ rays observed were at 288 kev (15%), 590 kev (15%), 720, 1190, and 1280 kev (last three less intense). The photopeak at 288 kev represents two coincident $\gamma$ rays of about the same energy. Tentative spin and parity assignments were made for the ground states of the nuclides investigated. Mass assignments were confirmed by a study of the relative yields of the various radioactive isotopes as the bombarding $\alpha$-particle energy and isotopic composition of the Ru target were varied.