Positron states in alkali-halide single crystals

Detailed consideration is given to the annihilatory decay of positron states in real alkali-halide single crystals of defective structure. Representations of the exciton-positron states in the matrix of the crystal and close to a lattice defect are analyzed. On the basis of these representations, expressions are derived for the yield of the three-quantum decay process and the intensities of the components contributing to two-quantum annihilation; the expressions agree with existing experimental data. It is shown that the greatest contribution to the three-quantum decay arises from an exciton-orthopositronium state located in the vicinity of the defect.