The evaporation of metals by fission fragments

Abstract

The number of atoms evaporated from the surface of a metal during the emission of fission fragments or alpha particles from it has been measured, using U 233 and Pu 239. This number is markedly dependent on the presence of a surface layer of oxide; for the emission of fission fragments from U 233 it increases from 24 to 1200 when the oxide film is removed. For Pu 233 with an oxide-free surface the number is 3500 atoms per fission fragment. For Pu 239 undergoing spontaneous decay 0·02 atoms are evaporated for each alpha particle emitted. An approximate calculation indicates that the number of atoms in the zone heated by passage of a fission fragment to the temperature necessary to cause evaporation is, for uranium, 5·6 × 10 6. The amount of kinetic energy transferred from the fission fragment to the atoms of the lattice is evidently greater than the value at present accepted in the literature.