Exploitable results Research and development on fundamental properties and production techniques for fast scintillating crystals for use in high-energy physics experiments The main results of R&D work on this INTAS project are as follows: The light yield of cerium fluoride scintillators can be increased by its structure modifications, which result in the creation of acceptor levels above the top of the valence band (e.g. by oxygen doping). The mechanism of the increase consists in the shift of the wavelength of the light emissionz induced by the electron transitions from 4f cerium sublevels to the valence band, towards the transparency spectral region of cerium fluoride. An economic way to increase the length of cerium fluoride crystals up to the level, satisfactory the requierements of electromagnetic calorimeters, has been developed. The method consists in accumulating long crystals from several smaller parts by deformation welding. Deformation welding is made by pressing of the pieces to be connected to each other at temperature, corresponding to the local plastic deformation in the interfaces between the pieces. The temperature and pressure, necessary for deformation welding of cerium fluoride, can be decreased sufficiently by using of much more plastic intermediate layer between the pieces with the refractive index close to that for cerium fluoride. The crystals, applicable for the intermediate levels, are CsJ, PbF2 and some others. The main reason of catastrophic temperature quenching of lead fluoride crystals has been found to be connected with structural nonstabilities, induced by high fluorine ions mobility and the tendency of the cubic lead fluoride to be transformed to the orthorombic phase. It has been proved experimentally, that the transformation of the cubic lead fluoride to the stable orthorombic phase or stabilization of the cubic phase at room temperature by fluorine atmosphere annealing increase the light emission effectivity of lead fluoride by many times. The main factors, responsible for the deterioration of lead tungstate scintillation properties (decrease of the light yield, elongation of scintillation decay time, low radiation hardness), are connected with intrinsic structural defects. These defects are induced by deviations from stoichiometric chemical composition and presence of microscopic inclusions of secondary phases. The mechanism of the influence of these defects on scintillation characteristics is connected with trapping of non-equilibrium electrons and holes by deep levels in the forbidden gap of lead tungstate and with separation of electron excitations by local electric fields, induced by secondary phase inclusions (e.g. tungsten oxide clusters). So in order to avoid the deterioration of lead tungstate characteristics by intrinsic structural defects, methods of control and regulation of intrinsic defects structure in lead tungstate should be developed. Searching for OpenAIRE data... There was an error trying to search data from OpenAIRE No results available
