Positron Annihilation in Metal–Ammonia Solutions

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Abstract
The momentum distribution of photons from positrons annihilating in liquid sodium–ammonia solutions of several concentrations was found to be concentration independent and the same as that of previously measured LiNH3 liquid solutions. Single‐concentration angular correlation measurements made on KNH3 and RbNH3 liquid solutions showed the same momentum distribution as the LiNH3 and NaNH3 liquid solutions. In the case of LiNH3 and CaNH3 solutions, which retain their metallic characteristics even when frozen, freezing leaves the general shape of the momentum distribution essentially unaltered. When a dilute NaNH3 solution was frozen, the angular correlation of photons from positrons annihilating in the solid was found to be identical with that obtained from annihilations in pure solid NH3. This is indicative of precipitation of the sodium at the time of freezing. The angular correlations of photons from positrons annihilating in saturated liquid LiNH3, solid LiNH3, and solid CaNH3 show the same distribution at high momenta together with a concentration‐dependent narrow component. As the solvated electron concentration is increased, the narrow component broadens slightly and the percentage narrow component decreases. Interpretation of the data suggests a large percentage of positronium formation.