The L/K electron capture ratio in first-forbidden 81gKr decay

Abstract

The L/K electron capture (EC) ratio of 81g Kr was measured to be 0.146±0.005 utilizing the wall-less, anticoincidence, multiwire proportional counter technique and a reactor-produced, mass separated 81g Kr source. From this value, the Q EC and log ft values were determined to be 305 −29 +38 keV and 11.6 respectively, assuming EC decay only to the ground state. If there is 4 % EC branching to a reported 276 keV level, Q EC becomes 322 −14 +31 keV from which (L/K) g.s. = 0.144 ± 0.005, log ft = 11.6 for EC to the ground state, (L/K) 276 = 0.213±0.005, and log ft = 11.4 for 4 % feeding to the 276 keV level. In order to be confident of these results, an extensive systematic comparison of experimental and theoretical L/K ratios was made for both first-forbidden non-unique and unique transitions. From this comparison, a 7 2 + ground state assignment for 81 Kr is confirmed.