The positive muon and the positron as probes of defects

Conclusions A brief but hopefully general comparison has been made between muons and positrons as probes for the study of defects in metals. Since muon experiments are not only more demanding in manpower, cost and availability than positron experiments, they should be carefully designed in light of the knowledge that the muon is extremely sensitive to both intrinsic and extrinsic defects. Initial experiments should provide estimates of the muon diffusion coefficients as a function of sample temperature. High temperature hydrogen diffusion measurements do provide quidelines, although so far most of the observations of muon trapping have been made at low sample temperatures where hydrogen diffusion data do not exist. Given that the diffusion constant is known as a function of temperature, high-purity Fe²⁶ after low temperature electron irradiation is therefore a good candidate to study with muons. Since the defect type and concentration can be controlled in electron irradiated samples, such investigations could confirm the stated values of the diffusion constants in Fe thereby providing a new method for evaluating diffusion coefficients below Stage III in different metals.All the samples should be initially characterized by other less costly techniques to obtain, where possible, the concentration and type of extrinsic and intrinsic defects. Both transverse and longitudinal measurements should be made to unravel the question of different diffusion mechanisms versus defect-, impurity- or self-trapping.Provided that the full capabilities of the muon are utilized and coupled with complementary techniques, i.e., positron annihilation, the muon will constitute a useful new probe in deepening our understanding or defects in metals.Work supported by the US Dept. of Energy under contract DE-AC02-76CH00016.