Anomalous annihilation of positrons in several solid hydrocarbons

In previous experiments with positrons annihilating in liquid organic materials (Hogg et al.) the measurements of I N (intensity of the low momentum component from angular correlation data) and I 2 (intensity of the long lived component from lifetime measurements) have resulted in I N = I 2 /3 within experimental error.For samples of CH 4 , C 6 H 6 , and C 6 H 12 measurements in the liquid state yield the expected equality between I N and I 2 /3. However, in the solid state for these substances there is a marked disagreement between I N and I 2 /3. The value of I N , in all cases, is essentially zero suggesting that no positronium is formed, but the value of I 2 remains large.