Atmospheric Burnup of a Plutonium-238 Generator

The stratospheric inventory of the plutonium-238 resulting from the disintegration of a nuclear auxiliary power generator (SN AP-9A) in early 1966 accounts for essentially all the plutonium present in the original generator that reentered the atmosphere. Consequently, the pyrophoric $^{238}$Pu must have completely burned up during reentry and ablated into small particles. The arithmetic mean of the distribution of the $^{238}$Pu particle size was estimated to be 10 millimicrons, which confirms this conclusion.