Particle emission from polycrystalline and monocrystalline niobium under 14.1 MeV neutron impact

A brief review of recent results on particle emission from cold-rolled and annealed niobium with coarse surface finishes, and from monocrystalline niobium surfaces under 14.1-MeV neutron impact is given. For the cold-rolled and annealed samples two types of deposits were discovered on collector surfaces facing the irradiated targets. One type appeared as a fractional atom layer covering the surface, the other in the form of chunks. No chunk emission was observed for the monocrystalline niobium surface. The chunk deposits on the collectors facing the cold-rolled samples are not uniformly distributed over the collector area but are clustered along certain streaks or appear in patches. Furthermore, the number of chunks per unit collector area and the average chunk size were larger for the rough, cold-rolled samples than for the annealed samples. These observations suggest that the release of stresses (e.g. stresses caused by cold-rolling) in the surface regions by the energy deposited by primary recoils, and surface roughness affect the chunk emission significantly. Previously reported crude estimates of sputtering yields were improved on the basis of information which has become available from additional neutron irradiation runs