Sputtering with neutrons

Abstract

Any radiation causing damage in the bulk of a material also causes sputtering, i.e. the release of atoms at the surface. For neutrons, we have to distinguish between backward, forward and isotropic sputtering, depending upon the direction of the neutron flux. The sputtering yields, defined as the mean number of atoms removed from the surface per incident neutron, are generally expected to be proportional to the specific damage energy deposited in the surface layers or the damage energy cross-section, $ ̌ σ n ( E) v( T). The cross-section, σ n ( E), refers to elastic and inelastic scattering as well as the different nucle reactions. If the primary knock-on atoms are radioactive their emission yield can be detected separately. Generally, neutron sputtering yields are of the order of 10 −5 atoms per neutron, except for materials containing fissionable atoms, where a yield of the order of 1 was reported. Even the sputtering yields measured in some detail, such as for Au and Nb, still give only upper limits. For very rough surfaces a small part of the material was found to be emitted as microparticles.