Angular correlation of γ–e cascades in thepresence of hyperfine splitting of nuclear levels and its possibleinfluence on CEM spectra

Abstract

The anisotropy of conversion electron emission in transitionsbetween separate magnetic sublevels and its effects on energy andangular resolved conversion electron Mössbauer spectra (CEMS) istreated theoretically. The angular dependence of the separate lines ina CEM spectrum is expressed through the “particleparameters” bk which enter in theexpansion in Legendre polynomials Pk(cos Θ).The values of bk were obtained from the tables ofHager and Seltzer (Hager, R. S. and Seltzer, E. C., Nucl. DataA4, 397 (1968)) by extrapolation. For the M1 transition in57Fe the value of bk was not found inthe literature and new calculations were done which gavebk = +0.017. It turns out that for low energyMössbauer transitions of M1 character (57Fe,119Sn, 125Te, 169Tm) the angulardistribution of the conversion electron emission is almost isotropic(bk ∼ 0.01-0.06) and relative line intensitiesin CEM spectra differ from those in the absorption spectrum by no morethan to 2–5%. For EL transitions this angulardistribution is strongly anisotropic, so the shape of the magneticallysplit CEM spectrum depends on the angle of electron emission. Theconsidered effect could be observed for electrons emitted from smalldepths and it should be taken into account if correct informationabout thin layer magnetism is to be obtained fromCEMS.