Ortho-Positronium Reactions in Water Studied by Positron Annihilation Age-Momentum Correlation

Abstract

Temperature dependence on S(t), positron age dependent shape parameter of annihilation gamma-rays, in water was observed. S(t) at the ortho-Ps pick off annihilation time region were higher at higher temperatures. It is indicating that there are more reactions of ortho-Ps at higher temperature. Hence it was successfully indicated that the longest lifetime, i.e. ortho-Ps component, on positron annihilation lifetime spectra for water could be shorter at higher temperatures. The radical reactions, such as PsOH formation or ortho-Ps oxidation by hydroxyl radicals, are spin dependent reactions. The geminate pair of ortho-Ps and hydroxyl radical in water can give spin dependent reaction and the enhancement of S(t) with certain time interval, i.e. quantum beats, were expected. It was observed even for water at 11°C. It is probably indicating the hyperfine coupling constants of hydroxyl radicals in water.

Formation of Quasi-Free and Bubble Positronium States in Water and Aqueous Solutions

“…1 2) The 3-E analysis cannot describe the behaviour of the S-parameter (characterizing the shape of the Doppler spectrum) with time at short times, the so-called "juvenile broadening" effect, Fig. 2 [2] (data on S(t) in pure H 2 O obtained by conventional AMOC technique is in [3]). This effect consists in a decrease of the Sparameter when we go from "para-Ps times" (~100-200 ps) to the negative times; 0.45 0.5…”

Positron Annihilation Methods by Use of LSO Scintillators

“…Hence, the lifetime is shorter at higher temperatures [11]. The evidence of existence of the reactions of ortho -Ps was obtained by AMOC measurement [12]. Table I.…”