Note on the Pt and Hg mass-197 isomers

Abstract

The decays of Pt 197, Pt 197m, Hg 197 and Hg 197m into the levels of 79Au 197 have been examined with use of semiconductor detector spectrometers. Gamma-ray spectra were recorded with lithium drifted germanium detectors, and internal conversion coefficients were measured with an electron-gamma spectrometer employing both silicon and germanium detectors. These conversion coefficients were determined: the 191 keV transition in Au 197 following Pt 197 decay, ε K = 0.69±0.07, K/L = 5.2±0.6; the 346 keV transition in Pt 197m, ε K = 3.9±0.4, K/L = 1.8±0.2. The 191 keV transition is interpreted as having multipolarity M1+(≈28%) E2, and the 346 keV transition is M4. Details of the decay schemes are discussed. From the observed decay patterns of Pt 197 and Pt 197m, spin assignments 1 2 − and 13 2 + are made for these isomers, respectively. The spin of the 268 keV level in Au 197 is interpreted as 3 2 + , consistent with the “core-excitation” interpretation of these levels by Braunstein and de-Shalit. The reported existence of a level in Au 197 at 155 keV was not confirmed, and a reported weak 407 keV radiation from the decay of Hg 197m was not observed. The absolute transition probability of the 202 keV E2 radiation connecting the 279 keV ( 5 2 +) nd 77 keV ( 1 2 +) states is discussed, within the framework of the de-Shalit model and also that of Kisslinger and Sorensen.