Half-life of32Si

Beta rays from a 32 Si 32 P source, produced in 1968–1969 via the 30 Si(t,p) 32 Si reaction using a Van de Graaff beam at E t = 3.4 MeV, were counted with an end-window gas-flow proportional counter system including an automatic precision sample changer. Comparison counts were taken on the β rays from a 36 Cl source. Measurements beginning February, 1982 were made at approximately 4-week intervals, each consisting of a total of 40 hours of counting on each sample. The decay rate was determined from the 32 Si/ 36 Cl ratio of counts. Small periodic annual deviations of the data points from an exponential decay curve were observed, but are of uncertain origin and had no significant effect on the result. Based on the analysis of 53 points taken in 48 months, the value T 1/2 = 172(4) yr is adopted for the half-life of 32 Si. This result is substantially greater than two previously reported measurements of 108(18) yr and 101(18) yr but is lower than values based on geophysical evidence.