The enhancement of positronium yields by the hydroxide ion in the radiolysis of water

Abstract

Measurements of o-Ps yield and quenching rate have been made at 21°C in aqueous solutions of sodium hydroxide up to 8 M. The observed enhancement is considered within the spur model and attributed to the scavenging of H 2 +O by the OH - ion with an estimated scavenging constant K = 0.354 M -1. By making use of the measured yields of H 2, OH . and e aq - from long time-scale experiments we can estimate the ratio of the reaction rates of an epithermal electron state. The Ps enhancement coefficient may then be related to these reaction rates and the scavenging constant of H 2 +O. The decrease in equivalent conductance with increasing NaOH concentration up to ∼ 12 M suggests the importance of associated and dissociated OH - species. When the total NaOH concentrations are re-expressed as concentrations of dissociated OH - ions a linear increase in o-Ps intensity is found. The fitted enhancement coefficient bears excellent agreement with that estimated from the foregoing consideration of reaction rates. Our analysis shows that the relative yields of both Ps and e eq - should be in agreement. Within experimental error the data from pulse radiolysis shows that this is in fact the case.