AN INVESTIGATION ON THE DISTRIBUTION OF COUNTS IN POSITRON-ANNIHILATION LIFETIME SPECTRA

Positron annihilation lifetime spectra with a high number of counts gi ve useful information for various purposes (like accurate determinatio n of distributions of lifetimes or a comparison among competing models ). This requisite, coupled to the need of a good resolution, implies l ong times of measurement; the consequent instrumental drifts can degra de the quality of the data. In this paper a statistical analysis of sp ectra of polyethylene terephthalate is presented, which reveals that t he distribution of counts displays deviations from the expected Poisso nian behaviour, as a consequence of the jitter of the time zero. By me ans of a simple method for the compensation of such fluctuations it is possible to recover almost ideal statistical properties. (C) 1998 Els evier Science B.V. All rights reserved.