Helium-induced hydrogen recoil analysis for metallurgical applications

Abstract

A number of studies of hydrogen in metals require special capabilities not easily met by the usual nuclear reaction analysis techniques (NRA). As part of a study of hydrogen redistribution in stressed metals, hydrogen concentrations had to be measured with high statistical accuracy (one percent or better) in short times (of order 10 s) and without significant ion beam effects on the sample. Our method has been to measure the energy spectrum of protons projected out of thin metal foils at 0° by 3.5–5.0 MeV 3He and 4He ions which have elastic scattering cross-sections orders of magnitude greater than Rutherford. Event rates of 2000 counts/s have been achieved with beam currents 10 nA for metal foils loaded with 10 at.% H. This technique is described and compared to the more usual NRA procedures. Its application to the study of H redistribution in stressed metals is briefly discussed. Recoil cross sections have been evaluated from known p- 4He phase shifts and tabulated for use in absolute measurements of depth profiles. These cross sections should also be useful in glancing-angle recoil geometries.