Evaluation of defect production cross sections and calculated fission-fusion neutron spectrum sensitivity

Abstract

A semi-empirical method is presented of deriving PKA cross sections for production of Frenkel pairs produced by irradiation of pure metals at liquid helium temperatures. Cross sections derived by this method were developed for copper, silver, molybdenum and tungsten. Neutron cross sections which were calculated by Heinish and Mann for mobile and clustered defects in copper were applied to a wide range of fission and fusion neutron spectra. These defect cross sections were developed from the computer simulation of the production and annealing of isolated binary collision cascades. The total number of defects per cascade were normalized to the semi-empirically derived PKA cross section for the production of Frenkel pairs by selecting an appropriate recombination radius. A study of the spectral sensitivity of mobile and clustered defects reveals that the relative numbers of mobile defects will be spectrally sensitive while clustered defects will be relatively insensitive to differences between fusion and most fission neutron spectra.