Condensed matter investigation by positron lifetime technique

Positron lifetime spectroscopy (PLS) was used to investigate various condensed matter samples, both pure and after certain treatments. The positron lifetime spectrum was measured for four pure alkali halides (NaCl, KCl, KBr, and KI). We concluded that, in a perfect ionic crystal, anion-Ps bonded state annihilation is the predominant process, and that each anion possesses approximately seven to eight electrons capable of annihilating with a positron. Pure silicon, copper, and nickel were analyzed by PLS, and we deduced that eight to nine electrons per atom in Ni and about ten electrons in Cu are inclined to annihilate with a positron. We also used PLS to study the effect of gamma irradiation in pure NaCl, KCl, KI, and KBr, and to determine the induced defect concentration in NaCl for different irradiation doses. The effect of annealing on irradiated NaCl was studied at different temperatures, and partial defect repair was observed through variations in the intensity of certain lifetime components. The evolution of lifetime and intensity was studied in samples of pure, unirradiated NaCl and copper annealed at different temperatures. This study revealed a dual annealing effect, which involves both creating and repairing defects through the application of heat. We studied neutron-irradiated silicon and concluded that bivacancies are the major defects produced by neutrons, although monovacancies are also created but disappear at room temperature. Finally, we used the PLS method to analyze an aqueous solution of KMnO4 at different concentrations and deduced the probability of positronium formation and the cutoff rate for each concentration.