Angular-Correlation Studies of Positron Annihilation in Copper-Nickel Alloys

Rectangular-slit detector geometry has been used to study the Fermi surface of three concentrations of nickel in copper. Measurements were made in the $〈111〉$ and $〈110〉$ directions on single crystals of the alloys with concentrations of 10, 50, and 90 at.% nickel. The belly radius of the Fermi surface is seen to decrease as the amount of nickel is increased. The radius of the necks in the $〈111〉$ direction, however, does not appear to change substantially with change in alloy concentration. These necks are easily detected at concentrations of 10 and 50 at.% nickel and are still visible in the 90 at.% nickel alloy.