The isotopes of curium, berkelium, and californium found in the thermonuclear debris of the November, 1952 thermonuclear test are discussed. The instantaneous buildup of the heavy elements in the thermonuclear device is compared with the buildup during pile irradiation. The alpha-particle energy (5.4 Mev) and the spontaneous fission half-life (<1.2×107 years) of Cm246 are reported. The spontaneous fission half-life of Cf254 was found to be 55 days. No other mode of decay was observed for this isotope.