Uncertainties in studies of Fermi surfaces by positron annihilation

A model Fermi surface for copper alloys, with variable neck radius and belly radius, is used to estimate the effectiveness of crossed-slit and long-slit techniques in detecting and measuring features such as necks on a Fermi surface. The model is applied to recent crossed-slit measurements of Cu-Ni alloys by Rouse and Varlashkin. It is found that their uncertainty in neck radius is considerably larger than that of the previous long-slit measurements, and that their failure to see a change in neck radius does not contradict the previous finding of a 0.2-mrad change in neck radius in these alloys.