The momentum distribution of positronium (Ps) in BaF2 single crystal has been investigated in a temperature range from 10 to 297K. The existence of the delocalized and localized Ps has been confirmed. The momentum distribution of the delocalized Ps, a central peak at zero momentum and satellite peaks at the momenta corresponding to the reciprocal lattice vectors, has a large width even at 10K. The width is almost independent of temperature. The behavior is different from that of the delocalized Ps in other ionic crystals. This indicates that the delocalized Ps in BaF2 is strongly coupled to the phonon field.
- Angular correlation of positron annihilation radiation
- Delocalized state
- Momentum distribution