Calculation of the angular correlation and the lifetime of positron surface states on metal surfaces

Abstract

Using a potential model for the surface of a metal and the revised Brandt-Reinheimer enhancement factor r ( n ) , we have calculated the electron wavefunction, the two-dimensional angular correlation and the lifetime of 2y annihilation from the AI( loo), A1(110), Al(111) and Cu(121) surfaces. We conclude that (i) the momenta of the electrons are filtered by the suridce potential; (ii) the momentum distribution of 2y annihilation is greatly constricted for both the parallel and perpendicular directions to the surface; (iii) it is possible to obtain simultaneously the observed isotropic angular correlation curve and the long lifetime of the positron surface state; and (iv) within a reasonable range of our model parameters, the isotropy of the angular correlation curve is rather insensitive to the parameter values. Our results are consistent with experiment.