New calorimetric determination of the half-life of 241Am

Commercially available americium oxide of about 98% purity was refined by ion exchange, extraction chromatography and oxalate precipitation. After reduction with lanthanum to americium metal, it was further purified by repeated sublimation at 11000C and a pressure of less than 1.3x10-4Pa. The remaining impurity content was determined by spectroscopic analysis to be 0.65%o. The amount of 237Np formed by decay of 241Am after the last sublimation was calculated to be 0.55%o. Repeated determinations of the heat output in a twin microcalorimeter resulted in 7659.8μW. From this value and from the 241Am mass of 66.783mg the specific heat output of 0.1147W/g, the half-life of 432yr and the decay constant of 5.084x10-11sec-1 were calculated. (author)