Decay of Neutron-Deficient Isotopes of Pd and Rh

Abstract

Pd isotopes of masses 98, 99, and 101 were prepared by $\ensuremath{\alpha}$-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\ifmmode\pm\else\textpm\fi{}0.1 minutes by emission of 2.5\ifmmode\pm\else\textpm\fi{}0.2 Mev positrons in coincidence with 650\ifmmode\pm\else\textpm\fi{}10 kev $\ensuremath{\gamma}$ rays. Its ${\mathrm{Pd}}^{98}$ parent was shown by successive daughter extractions to decay with a half-life of 17.5\ifmmode\pm\else\textpm\fi{}0.5 minutes. ${\mathrm{Rh}}^{99}$ (4.7\ifmmode\pm\else\textpm\fi{}0.1 hours) showed 0.74-Mev positrons (10%) in coincidence with 335\ifmmode\pm\else\textpm\fi{}10 kev $\ensuremath{\gamma}$ rays (70%). Other $\ensuremath{\gamma}$ rays were observed at 615\ifmmode\pm\else\textpm\fi{}15 kev (20%), 890\ifmmode\pm\else\textpm\fi{}20 kev (weak line coincident with 335-kev $\ensuremath{\gamma}$), 1.26\ifmmode\pm\else\textpm\fi{}0.03 Mev, and 1.41\ifmmode\pm\else\textpm\fi{}0.04 Mev (weak). ${\mathrm{Pd}}^{99}$ (21.6\ifmmode\pm\else\textpm\fi{}0.6 minutes) was identified by successive Rh daughter extractions. Its maximum positron energy is 2.0\ifmmode\pm\else\textpm\fi{}0.1 Mev and the following $\ensuremath{\gamma}$ rays were observed: 140, 275, 420, and 670 kev. The 140-kev $\ensuremath{\gamma}$ ray is the most intense and the 420-kev peak represents two $\ensuremath{\gamma}$ rays of about the same energy in cascade. ${\mathrm{Rh}}^{101}$ (4.7\ifmmode\pm\else\textpm\fi{}0.2 days) decays by electron capture followed by emission of 312\ifmmode\pm\else\textpm\fi{}10 kev $\ensuremath{\gamma}$ rays. ${\mathrm{Pd}}^{101}$ (8.5\ifmmode\pm\else\textpm\fi{}0.3 hours) emits 0.58\ifmmode\pm\else\textpm\fi{}0.04 Mev positrons (4%) by decay to the ground state of ${\mathrm{Rh}}^{101}$. The $\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}$ 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 $\ensuremath{\alpha}$-particle energy and isotopic composition of the Ru target were varied.