Inhibition and enhancement of positronium formation in aqueous solutions from the Doppler broadening of annihilation peaks

The Doppler broadened positron annihilation line shapes have been determined in aqueous solutions of various inhibiting and enhancing agents of positronium (Ps) formation : H+aq, NO−3, S2−, SCN− and the halide ions. The results confirm that the inhibition is made through electron scavenging by H+aq and NO−3, and through positron capture, to form a bound state, by the other ions. The characteristics and yields of the various positron-containing species in the solutions are inferred from the deconvoluted experimental line shapes. On referring to the lifetime spectroscopy experimental data, it is found that the yields of positron bound states are lower than expected, and the formation of excited states is hypothesized to account for the discrepancy.