ON THE STRUCTURE OF IRRADIATION-INDUCED COLLISION CASCADES IN METALS AS A FUNCTION OF RECOIL ENERGY AND CRYSTAL-STRUCTURE

The binary collision code MARLOWE is used to study cascade sizes, defect densities and subcascade configurations in f.c.c., b.c.c. and h.c.p. metals as a function of recoil energy up to 1 MeV. The threshold energies for the formation of subcascades are determined using a definition based on the defect configuration after the collisional phase of the cascade. A computational method was devised for identifying subcascades, and it was used to determine the number and spacing of subcascades as a function of recoil energy. The results are presented to illustrate the effect of recoil energy, atomic mass density and crystal structure on cascade volume and vacancy density after the collisional phase of the cascade, and on the number of subcascades and the subcascade spacing. The cascade morphology in the collisional phase sets the initial conditions for defect production and clustering during the development of each cascade, as well as influencing the global evolution of the microstructure. Comparisons with experimental observations illustrate fundamental differences in cascade structure for cascades of high and low energy density.