A positron study of pure and of L-alanine doped triglycine sulphate

Abstract

Positron lifetime spectra in TGS and in LA-TGS obtained between O°C and 75°C, can be analyzed in two components with lifetimes of about 230 ps, with an intensity of 80%, and 500 ps. The rather large uncertainties found for these values at temperatures higher than 15°C may have their origin in thermally stimulated electron emission from the crystals, making the system unstable in such a way that the ferroelectric transition is not observed. The short lifetime, which is sensitive to the concentration of L-alanine in the samples, is to be associated to the annihilation from a relatively free positron state, whereas the long-lived component is attributable to the annihilation of positrons from a not well known bound state which may be quasi-positronium.