Self-Irradiation Damage in Actinide Metals and Alloys

Abstract

This review covers the effects of self-irradiation damage on the physical properties of the α-emitting actinide metals Th, Pa, U, Np, and Pu and some of their alloys: compounds are not considered. The damage to the lattice caused by the α-particles and recoiling nuclei anneals out below room temperature so that the experiments have to be carried out at cryogenic temperatures, mainly in liquid helium. The properties that have been studied include resistivity, length, lattice parameters, thermal conductivity, and specific heat. Most work has been done on the resistivities. These increase with time, showing an exponential approach to saturation after some thousands of hours. In addition to the main exponential law, smaller exponential terms can be separated in some cases, indicating that more than one damage mechanism occurs. The lengths and lattice parameters also saturate exponentially. For most materials these increase but the metastable phases β- and δ-plutonium contract with time. Because the α-particle and, particularly, the recoiling nucleus have only short ranges in these metals, large numbers of atoms are displaced from the lattice in a small volume. The defects are thus not independent of each other, and this, combined with the complex electronic and crystal structures of the actinides, makes calculations on the detailed structure of the defects very difficult. The subject has therefore been approached from a phenomenological standpoint.