The decay of Tb 158(150y) to levels in Gd 158 and Dy 158

Abstract

The long-lived Tb 158 electron-capture decay to levels in Gd 158 and beta-decay to levels in Dy 158 have been studied by means of scintillation spectrometers, Ge and Si semi-conductor detectors, gamma-gamma and negaton coincidence measurements, directional correlation techniques and half-life measurements. The gamma-ray transitions (with total intensities in per cent of total Tb decays) observed are 79.5(83.8%), 182(12.5%), 782(9.9%), 928(0.2%), 946(46.7%), 964(22.2%) 1110(2.2%), and 1190 keV (1.8%), in Gd; 99.0(14.5%) and 218 keV (1.4%) in Dy. The K conversion coefficient measurements and directional correlation measurements are consistent with E1 assignments for the 782, 946 and 964 keV transitions. The following levels in Gd 158 have been established or confirmed: 79.5(2 +, T 1 2 = 2.47 ns) , 262(4 +), 1026(2 −), 1044(3 −, K = 1), and 1190 keV (2 +, K =2). The decay proceeding to the 1190 keV level is >95% L electron capture. An 857±27 KeV beta branch (log ft=12.1) proceeds to the 99.0 keV (2 +, T 1 2 = 1.64 ns) level in Dy. A weak inner beta branch (<1.5%) feeds the 317 KeV (4 +) level in Dy 158. Comparisons are made with the theoretical estimates for the transition branching ratios for K forbidden transitions.