Temperature Dependence of the Inhibition of Positronium by Chlorine- Substituted Hydrocarbons in Non-Polar Liquids

Positron annihilation lifetime spectra were measured for solutions of 1,2,3,5-C6H2Cl4 in hexane, toluene, m-xylene and mesitylene, CCl4 in hexane and toluene, and C2HCl3 in n-hexane for concentrations below 1 M and at various temperatures between −30°C and 67°C. The Ps inhibition by C6H2Cl4 was roughly 14 times stronger at −30°C than at 67°C in toluene, m-xylene, and mesitylene, while that of CCl4 displayed hardly any temperature dependence in hexane and toluene. Previously, the Ps inhibition by C6H2Cl4 in various liquids at 20°C was explained by a competition between electron pick off by the positron from C6H2Cl4− formed by electron scavenging in the positron spur, and dehalogenation of the same anion at picosecond times after the spur formation. Three effects might reasonably explain the strong temperature dependence of the Ps inhibition of C6H2Cl4: (1) The dechlorination time of C6H2Cl4− might be much shorter at low than at high temperatures. (2) The positron mobility might decrease very strongly with decreasing temperature. (3) Positrons possibly trapped on C6H2Cl4 might thermally detach at high but not at low temperatures.