Inhibition of Ps Formation by Strong Ps Quenchers

Positron lifetime spectra for aqueous solutions of NaIO4, KMnO4, K2Cr2O7, and CuCl2 were analysed to obtain lifetimes and relative intensities for the long- and short-lived components which are mainly due to ortho- and para-positronium (Ps) respectively. The problems of analysis are discussed in some detail. The Ps quenching and inhibition constants were found to be 2.6 × 1010, 2.6 × 1010, 1.6 × 1010, 2.7 × 109 M−1 s−1 and 18, 18, 13, 2.5 M−1 for the ions IO−4, MnO−4, Cr2O2−7, and Cu2+ respectively, and the quenching constants for CuCl+ and CuCl2 to be (5 ± 3) × 109 and (12 ± 7) × 109. In terms of the spur reaction model of Ps formation, possibilities are discussed of obtaining a theoretical expression for the Ps yield versus electron scavenger concentration. It is concluded that an empirical formula must be used. It is argued that most Ps formation and inhibition takes place within a few psec as results of “dry” electron reactions. Ps inhibition studies may therefore give information about “dry” electron reactions with scavengers.