Gorbachova T. Specific features of scintillation signal formation in organic monocrystalline, polycrystalline and composite scintillators

Thesis for the scientific degree of candidate of physical and mathematical sciences by speciality 01.04.10 - Physics of semiconductors and dielectrics. - Institute for Single Crystals of NAS of Ukraine, Kharkiv, 2017 The dissertation is devoted to the investigation of the influence of deep traps of structural origin those arise in composite and polycrystalline scintillators based on stilbene, anthracene, p- terphenyl and activated p- terphenyl on their optical and scintillation characteristics. The influence of deep traps on the mechanism of formation of the scintillation signal is proposed. It is proved that the formation of deep traps of charge carriers in polycrystalline scintillators leads to a decrease of the light yield and decay time in comparison with single crystal samples. The time of localization of charge carriers on deep traps is by several orders of magnitude longer than the scintillation signal shaping time 2 мs. Light-collecting coefficients were determined using the model of discrete optical medium of for polycrystalline and single crystal scintillators. These coefficients were used for calculation of the light yield. The light yield of scintillation materials of the same chemical composition has close values. The patterns of changes in the light output associated with the increase in the average length of the light path to the detector's output window were found both in the case of transition from single crystal to polycrystalline sample as well as in the case of transition from volume to local excitation. Key words: radioluminescence, scintillators, traps, light output