Engineering of long length CsI:Tl scintillators for high energy physics

It is shown that engineering of long length CsI:Tl scintillators for medium and high energy physics projects significantly depends of the primary performance of scintillation single crystal. In particular statistical study on several hundred samples for different project justify significant role of the Tl concentration. Tl concentration gradient along the bar and final finishing (stability of surface roughness for the light collection tuning) in the technology optimization for scintillator production. It is necessary to note, that any of these parameters are not taken into account in the Monte Carlo simulation (Geant 4) that usually use as the start point for the scintillator optimization

Fluctuations of ionizing particle track structure and energy resolution of scintillators

The work is devoted to the study of fluctuations in ionizing particle track to the energy resolution deterioration. Reasons of deterioration of energy resolution of scintillators due to relatively rare events of production of high-energy Auger and delta-electrons are discussed in terms of different decay from regions with different concentration of excitations in track region. The model allows to assume that decay time changes reflect track non-uniformity and following energy resolution changes. The shallow traps which change the mobility of charge carriers could influence the long components of the decay and therefore modify the input to scintillation signal from regions with low concentration of excitations. This effect could be significant in deterioration of energy resolution of scintillators

Advanced method of scintillator energy resolution test

This work is devoted to the development of advanced method of scintillator energy resolution test. Separation of scintillation photons for different groups in accordance with statistical methods allows to extract some groups of photons that give better resolution values comparing to conventional approach. It is shown that new method could be useful for analysis of scintillation uniformity of detector

The heat transfer model for VGF technique with skull layer for halide crystal growth

The work is devoted to the investigation of the key parameters for reproducible skull technique of NaI based crystals. Combination of math simulation (CGSim software) with experimental measurements of the temperature distribution during the raw material heating, melting stage and later crystallization gave not only approval of the methodology but allowed to grow scintillation crystal with the same performance as typical for single crystals. The obtained results are applicable for the skull layer thickness minimization, melting and crystallization stages verification and estimation of the gradient for proper convection and crystal homogenization. As result the medium size (250× 180× 45 mm³) NaI crystals were obtained

Radiation induced defects in M₁₋ₓPrₓF₂₊ₓ (M²⁺ = Ca, Sr, Ba, x = 0.35) solid solutions

Radiation-induced processes in M₁₋ₓPrₓF₂₊ₓ (M²⁺ = Ca, Sr, Ba, x = 0.35) solid solutions have been studied. It is shown that the radiation coloration of M₀.₆₅Pr₀.₃₅F₂₃₅ crystals is due to the trapping of charge carriers at anion sublattice defects. The efficiency of color centers formation in the investigated solid solutions grows in the row Ca —> Sr —> Ba. It may be caused by the increase of the pre-irradiation defects as a result of the different cluster types formation in M₀.₆₅Pr₀.₃₅F₂₃₅ mixed systems

The stress-strain state of deformed NaCI type single crystals with the sample height smaller than the base side

A real modelling of the mass transfer process in a crystal by visualization of the crystal material motion under deformatioin using markers as well as structure studied have revealed inhomogeneity in the stress fields and in the crystal dislocation structure. Four crystal regions have been distinguished differing in the dislocation structures and the dislocation interaction mechanisms. For each region, the structure evolution has been studied and the structure state diagram has been constructed as a function of the prestrainin rate

Deep traps in KMgF₃ and LiBaF₃ crystals

The influence of the high temperature annealing in air to the deep traps formation in KMgF₃ and LiBaF₃ fluoroperovskites was the subject of this study. An additional absorption and blue emission connected with O²⁻ ions presence in annealed crystal were revealed. The thermal destruction of colour centres in x-irradiated samples is accompanied by intensive recombination luminescence in high temperature TSL peaks. This phenomena was explained by pyrohydrolysis of crystal surface and oxygen diffusion into the crystal volume. Hydrolysed crystals were found to store the energy under UV irradiation.Работа посвящена изучению влияния высокотемпературного отжига на воздухе на образование глубоких ловушек в флюороперовскитах KMgF₃ и LiBaF₃ . Обнаружено, что в отожженных кристаллах возникает дополнительное поглощение и "синее" свечение, связанное с присутствием O²⁻ ионов. Термическое разрушение центров окраски в образцах, облученных рентгеновским излучением сопровождается интенсивной рекомбинационной люминесценцией, проявляющейся в высокотемпературных пиках ТСЛ. Это явление может быть объяснено пирогидролизом поверхности и диффузией кислорода в объем кристалла. Показано, что гидролизованные кристаллы запасают энергию при УФ облучении.Роботу присвячено вивченню впливу високотемпературного відпалу на повітрі на утворення глибоких пасток у флюороперовскітах KMgF₃ i LiBaF₃. Виявлено, що у кристалах після відпалу виникає додаткове поглинання і "синє" світіння, яке пов’язане з присутністю O²⁻ іонів. Термічне руйнування центрів забарвлення в зразках, опромінених рентгенівським випромінюванням, супроводжується інтенсивною рекомбінаційною люмінесценцією у високотемпературних піках ТСЛ. Це явище може бути пояснено пірогідролізом поверхні та дифузією кисню в об’єм кристала. Показано, що гідролі-зовані кристали накопичують енергію під дією УФ опромінення

Scintillation characteristics of deformed large-sized NaI crystals

The effect of plastic deformation on defect structure and functional parameters of NaI based crystals and scintillator NaI(Tl) in particular has been studied. Plastic flow modeling in decorated samples as well as in large size crystal blanks demonstrated significant non uniformity of the deformation map along the sample. Scintillation parameters (light output and energy resolution) are practically the same through the whole crystal volume. Post deformation scintillation parameters are similar to the single crystal ones. This phenomenon is typical for the wide range of temperature and deformation rates for this type of crystals

Unidimensional position sensitive detector

It has been shown that a predetermined distribution of the light yield along the length of scintillator can be achieved by treatment of the side surface of Csl(TI) crystal. A principle and of manufacturing a position sensitive detector have been considered. The dependence of the detector position resolution on its size has been studied.Показано, что предопределенное распределение светового выхода вдоль длины сцинтиллятора может быть достигнуто обработкой боковых поверхностей кристалла Csl(TI). Приведены принцип и метод получения позиционно-чувствительного детектора. Изучена полученная зависимость позиционного разрешения детектора таких размеров.Показано, що наперед визначений розподіл світлового виходу вздовж сцинтилятора може бути досягнутий обробкою бічних поверхонь кристала Csl(TI). Наведені принцип та метод отримання позиційно-чутливого детектора. Вивчено отриману залежність позиційного розділення детектора таких розмірів