Characterization of displacement cascade damage produced in Cu3Au by fast-particle irradiation

Zones of reduced long-range order created at displacement cascade sites in well-ordered Cu3Au may be directly imaged in the transmission electron microscope so that quantitative information can be obtained on individual cascade events. This technique has been used to characterise the cascade damage created by three fast particles (3.5 MeV protons, a source of moderated fission neutrons and a source of fusion neutrons with energies peaking at 14.8 MeV) with the aim of comparing the experimental observations with the relevant collision models. In each case, disordered zone number densities, sizes and shapes were determined, and were found to be characteristic of each irradiation, with the sizes of disordered zones and the proportion of zones of complex shape increasing on going from 3.5 MeV protons to fission neutrons to fusion neutrons. The quantitative results are largely consistent with the different calculated primary recoil spectra, although in the fusion neutron case some discrepancies are found which cannot readily be explained by limitations in the experimental technique. More specifically, more and larger disordered zones are found than expected from the calculated recoil spectrum. Subcascade formation was observed only in the neutron irradiations, with the distributions of sizes and shapes of individual sub-cascades being very similar in the two cases (in marked contrast to those obtained from sizing total cascade events). Finally, the production of point-defect clusters at cascade sites was studied. The efficiency of cascade collapse increased on going from 3.5 MeV protons to fission neutrons to fusion neutrons. (orig.)