Effect of water-soluble electron scavengers on positronium formation in AOT/water/isooctane microemulsions

Abstract

In a previous work reporting on positron annihilation lifetime spectroscopy (LS) measurements in AOT/water/isooctane microemulsions, a model was established leading to the satisfactory description of both triplet positronium (o-Ps) formation and decay. The model proposes that a large proportion of Ps is formed in the aqueous pseudophase, a fraction of which can diffuse out to the organic phase. It thus predicts that an electron scavenger, soluble in the aqueous pseudophase only, should have an inhibiting action on both those species decaying in the aqueous (o-Psaq) and organic (o-Psorg) phases. To assess this prediction, measurements are performed with efficient inhibitors of Ps formation, incorporated into the reverse micelles: Te(OH)6, KNO3, and HgCl2. The last solute is also known as a Ps quencher in water. In all three cases, the lifetime results show that the radii of the water cores remain unaltered by the presence of the additives. As expected, the intensities of both o-Psaq and o-Psorg decrease with increasing solute concentration. However, the quenching power of HgCl2 is suppressed in the water aggregates; this is probably due to the association of the Hg2+ cations with the sulphonate groups of AOT. On this basis, the inhibition of HgCl2 is attributed to positron capture by the Cl- ions. The inhibition constant of Te(OH)6, KNO3 and Cl- are all found to be about 65% of what they are in pure water. Qualitatively, this is ascribable to the existence of mixed water-isooctane positron spurs.