Study of delocalized positronium in alkali halides by 2D-ACAR

Two-dimensional angular correlation of annihilation radiation (2D-ACAR) from KI and KCl 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. High sensitivity of the 2D-ACAR measurement has permitted us to detect the odd Miller index satellite peaks in KI for the first time. Not only the odd index peaks but all the satellite peaks except for the (200) peaks are very weak. The intensities are also calculated in two different approximations for the wave functions of the Ps in both crystals and compared with the experimental results.