Low energy positron diffraction study of NaF and other alkali halide surfaces.

We have measured the elastic backscattering probability vs. energy for positrons normally incident on various ionic crystal surfaces. The samples studied were (100) surfaces of LiF, NaF, NaCl, KCl and KBr cleaved in air and a polished (110) surface of CaF2. We observed Bragg peaks of several orders for each sample surface. We can explain the positions of the peaks by assigning an inner potential V(o) and a relaxed atomic plane spacing d for each crystal.