Surface positron and positronium states in real ionic crystals

Positron annihilation has been used to examine the positron and positronium states at the surfaces of (100) and (110) faces of KCl and KCl-5% AgCl single crystals. The measured and theoretical parameters differ from the analogous bulk values; exposure of KCl to Ps atoms produces mainly A₊, F₊, and D₊ centers. It is shown that this method can be used to examine surface states and surface electron-density distributions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 76–81, January, 1978.