Central Reactivity Contributions of ²⁴⁴Cm, ²³⁹Pu, and ²³⁵U in a Bare Critical Assembly of Plutonium Metal

Central reactivity contributions of gram-sized samples of ²⁴⁴Cm, ²³⁹Pu, and ²³⁵U have been obtained in a fast critical assembly of bare ²³⁹Pu in a spherical geometry. Resulting values are: ²⁴⁴Cm = (1276 ± 5%) cents/g at.; ²³⁹Pu = (1393 ± 3%) cents/g at.; ²³⁵U = (701 ± 2%) cents/g at. From these data, the critical mass of a bare sphere of ²⁴⁴Cm is estimated to be (27.7 ± 2.5) kg at a density of 13.5 g/cm³.