MAGNETIC QUENCHING OF POSITRONIUM IN SOME NONPOLAR SOLUTIONS
The magnetic quenching of positronium appears experimentally in the reduction of the long lifetime component in the lifetime spectra in the presence of an external magnetic field. In previous investigations in some solids (e.g. polymers, alkali halides, etc.) and water, the variation of the o-Ps lifetime with the field strength has been interpreted in terms of a shift of the value of the positronium hyperfine splitting constant, (DELTA)E. In the present study, the magnetic quenching of o-Ps in pure liquids (n-hexane, c-hexane and benzene), nitrobenzene in n-hexane, c-hexane and benzene solutions and carbon tetrachloride/n-hexane solutions is examined for fields up to 14 kG by the positron lifetime technique. The obtained spectra are analyzed into three lifetime components. The long-lived positronium lifetime, o-Ps, is the most sensitive component to the external magnetic field. The interpretation in terms of the hyperfine splitting constant can only distinguish the behaviour of positronium from the free atom. It is observed that in the case of pure liquids, dilute nitrobenzene in n-hexane, c-hexane, and benzene solutions and carbon tetrachloride/n-hexane solutions, positronium behaves normally; i.e., as the free atom. However, for 0.05M and 0.1M nitrobenzene/n-hexane solutions, an anomalously strong magnetic quenching is observed at low field, and at higher magnetic field strength, an anomalously weak magnetic quenching is observed. This unexpected behaviour of positronium in high concentrations of nitrobenzene/n-hexane solutions is interpreted in terms of the field effect on the interaction of triplet molecules and radical ions with positronium. The results depend very much on the solute concentration due to the yield of triplet states and radical ions generated in the solution. This implies a significant role of the interaction between nitrobenzene transient radiolytic species and the Ps atom. The same concentration range of carbon tetrachloride/n-hexane solutions are also investigated, and no anomalies are observed. The different results of these two systems may be due to the differences in spur processes in carbon tetrachloride solutions. The proposed mechanism is based on known effects involving delayed fluorescence and electrogenerated chemiluminescence (ECL) measurements, by assuming that positronium behaves as one of the triplet or singlet excited species which reacts with either triplet molecules or radical ions.
"MAGNETIC QUENCHING OF POSITRONIUM IN SOME NONPOLAR SOLUTIONS"
(January 1, 1985).
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