Two-dimensional 2γ angular correlation study of delocalized positronium in alkali halides

The two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) from KCl and KI single crystals at low temperatures has been measured. The intensities of the narrow peaks resulting from the Bloch modulation of the delocalized positronium (Ps) are studied. The intensities of the peaks except for those at the momenta corresponding to the (000) and (200) reciprocal-lattice vectors are very tow for both KCl and KI. The experimental results for KCl are compared with the calculations made by Zhang and Song. Calculations with simpler approximations are also performed for both KCl and KI.