POSITRONIUM DECAY AND FORMATION IN PARAFFIN WAX FROM POLARIZED AND UNPOLARIZED POSITRONS

Ps formation and decay in heterogeneous n-alkane samples (paraffin waxes) have been studied both in the solid and in the liquid phase; then, in the solid phase, the positron's residual degree of polarization was measured at the instant of Ps formation. Differently from what is already known in homogeneous n-alkane samples, Ps shows, many degrees below the melting point, a mean lifetime longer than that typical of the liquid phase; furthermore, the mean lifetime's values pertaining to the transition between solid and liquid do not show a sharp variation across the melting temperature but gradually decrease over a range of temperatures of several degrees. Positronium decay in static magnetic fields indicates that o-Ps magnetic quenching in liquid phase is regular, and corresponds to a contact density value alpha = \psi(0)\(2)/\psi(0)\(2)(vac) = 0.79 +/- 0.07; instead, in the solid phase, o-Ps magnetic quenching shows anomalous behaviour for fields weaker than 7 kG. Positrons' residual polarization measurements do not reveal the presence of depolarization effects during the whole slowing-down process until Ps is formed.