Quasielastic Coherent Scattering for Atomic Diffusion via Vacancies

Abstract

Quasielastic incoherent neutron scattering has long been recognized as a tool for obtaining microscopic information on diffusion /1/. This method has been used very successfully for the study of hydrogen diffusion in metals /2/. Unfortunately, there are very few isotopes with a sufficiently large incoherent scattering crosssection to allow diffusion experiments. Thus it seems worthwhile to look into the possibilities of quasielastic coherent neutron scattering (QECS). In this paper we give a preliminary account of theoretical considerations to understand which informations about diffusion in binary substitutional alloys can be expected from QECS. For the interpretation of such experiments explicit model calculations are needed. We suggest that for such calculations an extension of our method used to describe incoherent scattering /3/ due to diffusion via vacancies in pure metals /4/ and dilute alloys /5/ can be used. This method consists of approximately solving a hierarchy of differential equations for many-particle correlation functions /4–6/. The model parameters of such calculations are the jump frequencies of vacancies with the constituents of the alloy.