Americium 242m in nuclear test debris

Abstract

DIAMOND et al.¹ discussed the production, in a thermonuclear explosion, of isobars of mass numbers 239 and greater by neutron reactions on uranium, followed by β decay; much the same arguments seem to apply to phenomena in plutonium devices. Both cases, viewed in this way, suggest that mass number 241 will be represented by both ²⁴¹Pu and ²⁴¹Am, mass number 242 only by ²⁴²Pu, and mass number 243 only by ²⁴³Am. Such considerations neglect, however, the fact that weapons-grade plutonium is always more or less contaminated by ²⁴¹Am, and that this nuclide has an appreciable cross section (100 barn for thermal neutrons and slightly larger for epithermal neutrons) for neutron capture leading to ²⁴²Am; about 10% of such captures yield ^242mAm, the others going to the ground state. It seems, then, that one should expect to find in the debris from nuclear explosions not just two, but all three, of the long lived americium nuclides: ²⁴¹Am, ^242mAm and ²⁴³Am.