RADIOISOTOPES
Online ISSN : 1884-4111
Print ISSN : 0033-8303
ISSN-L : 0033-8303
Reactions between Positronium and Molecules Studied by an Age-Momentum Correlation Measurement
Akira UEDONORyoichi SUZUKIShoichiro TANIGAWA
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1992 Volume 41 Issue 12 Pages 611-617

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Abstract

High count rate correlation measurement between the lifetime of positrons and the momentum of an annihilating positron-electron pair was achieved by using the fast fast coincidence system. This system reads out data for energies of 7-rays produced by annihilations of positron-electron pairs and those for lifetimes of such pairs. These two types of digitalquantities were stored in a memory matrix of 32 channels (energy) ×256 channels (time) ×4 bytes (count) . The data acquisition was controlled by a microcomputer. The age-momentum correlation measurement was applied to studies of the Ps formation and its reactions with molecules in pure water, ice and solutions of MnSO4.From the measurements, it was found that reactions of Ps can be clearly observed from lifetime spectra measured as a function of the Doppler shift in annihilation γ-rays. In pure water, the self annihilation of para-positronium (p-Ps) and the pick-off annihilation of ortho-positronium (o-Ps) were observed. In solutions of MnSO4, the spin-conversion from o-Ps to p-Ps with a significantly narrow momentum distribution was found. This fact suggests that o-Ps is fully thermalized before the annihilation because of its long lifetime (-1 ns) . The present investigation shows the potential of the age-momentum correlation measurement for the Ps chemistry.

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© Japan Radioisotope Association
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