Papers by Author: Giovanni Consolati

Abstract: The detection of electron anti-neutrinos is generally carried out by searching for the coincidence of the reaction products, neutron and positron, in liquid scintillators. However, in these last a positron may form positronium (Ps) with an electron of the medium; efficiency of the process may be high. Furthermore, the triplet ground state sublevel (o-Ps) has lifetimes of a few ns. These features introduce distortions in the time distribution of the emitted photons, which is essential for position reconstruction and pulse shape discrimination algorithms in anti-neutrino experiments. This drawback can be favorably exploited by using o-Ps as a probe to detect anti-neutrinos in the scintillator. We report results of positron annihilation lifetime measurements in some organic liquid scintillators used for neutrino experiments. The o-Ps induced distortion of the scintillation photon emission time distribution may enhance the anti-neutrino detection.

Abstract: Polymerisation and polymer modification are often carried out by means of radiation methods, since irradiation can modify the structure of materials and improve their performance. On the other hand, combined action of ionising radiation and oxygen may induce a degradation of the polymer. Physical changes of different polyesters subjected to gamma irradiation up to 1 MGy are discussed and evidenced by various techniques, mainly viscometry, differential scanning calorimetry and positron annihilation lifetime spectroscopy (PALS). Viscometry monitors variations in the molecular weight. Calorimetric measurements allow one to detect crystallinity changes. PALS evidences possible irradiation effects on the free volume; furthermore, it supplies information on the chemical modifications induced by oxygen. The results can be explained in terms of the main mechanisms induced by gamma irradiation (chain scission, crosslinking and oxydative degradation), although their importance depends on the dose.