Temperature Effect on the Positronium Formation in Organic Solutions

Abstract

Studies of the temperature dependence of the rate constants for inhibition of o‐Ps formation in organic solvents show either zero or negative activation energies. This is additional evidence for the hypothesis that the experimentally observed inhibition rate constant k is the ratio of rate constants of two competing reactions, one being the reaction of the precursor of the thermalized o‐Ps with the solute (rate constant k), followed by annihilation and the second being the thermalization of this precursor (rate constant k2).

Effect of halogenated compounds on positronium formation in polycarbonate and polysulfone matrices

“…where C is the additive concentration in units of mol dm~3 , is the o-Ps yield at C \ 0, A is a constant related to the I 3 0 saturation value of and p is a Ðtting parameter, called the I 3 inhibition constant, which is related to the scavenging efficiency of the Ps precursor by an additive in comparison with the Ps formation efficiency. 4,12,16,26 sat from those in liquid benzene, the inhibition constants in the former system are very small compared to those in the latter system. A somewhat similar result was reported for in CuCl 2 poly(vinyl alcohol) and water by Mohamed et al 27 Tagawa studied geminate ion recombination in various substances by picosecond pulse radiolysis and found that the di †usion coefficient of spur electrons in a polymer (6 ] 10~6 cm2 s~1) is smaller than in molecular liquids (6.4 ] 10~4È6 ] 10~3 cm2 s~1).28 Thus, one may think that the lower inhibition constants in PC are due to a smaller di †usion coefficient of spur electrons in a polymer than in a liquid.…”

“…25 Alfassi and Ache measured Ps yields in toluene and decane solutions of various halogenated compounds as well as nitrocompounds. 16 These authors Ðtted the experimental results to the following empirical equation :…”