Readout technique of thermoluminescence calorimeter for large cascade detectors

Summary A spatial distribution readout system of thermoluminescence [TL] sheets is developed. This system consists of high-gain image intensifier, a CCD-TV camera, a video image processor and a host computer. This system has been applied to artificial TL sheets (BaSO₄: Eu doped) for detecting high-energy electromagnetic shower and to TLC pair meter for determining muon energy. To accomplish these aims, new techniques have been introduced for frame pictures of TL signals in electromagnetic shower:a) the self-correlation method andb) the mutual-correlation method.

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Riassunto Si mette a punto la distribuzione spaziale del sistema di lettura e trasferimento dalla memoria a fogli termoluminescenti (TL). Questo sistema consiste in un intensificatore d'immagine ad alto guadagno, una telecamera CCD-TV, un processore d'immagine video ed un elaboratore principale. Questo sistema è stato applicato a fogli termoluminescenti artificiali (BaSO₄ drogati con Eu) per rilevare sciami elettromagnetici ad alta energia e al TLC-pair meter per determinare l'energia muonica. Per raggiungere questi obbiettivi sono state introdotte nuove tecniche per fotogrammi dei segnali di TL negli sciami elettromagnetici:a) un metodo di autocorrelazione eb) un metodo di correlazione reciproca.

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Резюме Предлагается система термолюминентных пластин для определения пространственного распределения. Эта система состоит из усилителя изображения с высоким коэффициентом усиления, CCD-TV камеры, видеопроцессора и первичного компьтера. Эта техника применяется к искуссттвенным термолюминесцентным пластинам (BaSO₄, легированный Eu) для детектирования электромагнитных ливней высоких энергий и к TLC-парному счетчку для определения энергии мюонов. Для достижения этих целей были разаботаны новые методики: для считывания термолюминесцентных сигналов электромагнитного ливия,a) само-коррелированный метод иb) взаимно-коррелированный метод.

     

Simulation of competing irradiation and fading effects in thermoluminescence dosimetry

The aim of this article is to give some useful expressions for fading correction in practical situations as they can be encountered in radiation protection dosimetry monitoring, i.e. personal, environmental and clinical dosimetry. They are obtained considering the general case in which, for both first and second-order kinetics, during the experimental period of time two effects are in competition between them: one is the trapping rate due to the irradiation, the second is the detrapping rate which takes place at the same time, owing to thermal fading. Various practical situations are taken into consideration.     

Dependence of thermoluminescence response of calcium sulphate activated by dysprosium on the temperature irradiation

Radiation dosimetry is a very important issue in space research and in experiments that try to simulate chemical processes that may occur in cometary nucleus, interstellar grains, and other extraterrestrial environments, due to their irradiation by cosmic rays. The temperature effect is an important factor that has not been considered in many of these experiments. In this work, this effect was studied in TLD dosimeters exposed to gamma rays. The irradiations were done from 77 to 298 K in a Gamma cell unit with a dose rate of 1.0 Gy/s. Results obtained for CaSO₄:Dy show that there is a considerable effect in the evaluation of the dose as function of the irradiation temperature.     

Influence of electron irradiation on properties of semi-insulating GaAs detectors

The effects of electron beam irradiation on electrical and spectrometric properties of semi-insulating (SI) GaAs detectors were studied. The electric properties were monitored by reverse and forward current–voltage characteristics. In general, a breakdown voltage decrease with the dose was observed. However, some samples showed a local increase in the breakdown voltage at doses between 5 and 10?kGy. The detector spectrometric properties (the charge collection efficiency (CCE), the energy resolution and the detection efficiency) were evaluated from measured spectra of the ²⁴¹Am radionuclide gamma source before and after electron irradiation. The CCE and energy resolution showed minor changes after irradiation. The detection efficiency noticed an initial increase (up to a dose of 5?kGy) followed by a permanent decrease. At 30?kGy, the overall degradation of detector functionality was observed with all samples.     

1 MeV电子辐照对短波Hg1-xCdxTe光伏探测器的影响

研究了1 MeV电子辐照对短波Hg1-xCdxTe光伏探测器的影响。通过测试电子辐照前后光伏探测器的响应光谱、信号、噪声、暗电流等性能参数,分析了电子辐照对HgxCdxTe光伏器件的影响机制。实验结果发现：电子辐照后器件响应光谱在短波处有变窄的趋势,但响应峰值波长和截止波长基本无变化;随着辐照剂量的增加,通过p-n结的暗电流有所增加,光伏器件的探测率有减小的趋势。     

1 MeV电子辐照对短波Hg1-xCdxTe光伏探测器的影响

 研究了1 MeV电子辐照对短波Hg_1-xCd_xTe光伏探测器的影响。通过测试电子辐照前后光伏探测器的响应光谱、信号、噪声、暗电流等性能参数，分析了电子辐照对Hg_xCdxTe光伏器件的影响机制。实验结果发现：电子辐照后器件响应光谱在短波处有变窄的趋势，但响应峰值波长和截止波长基本无变化；随着辐照剂量的增加，通过p-n结的暗电流有所增加，光伏器件的探测率有减小的趋势。     

Spectrally resolved thermoluminescence of highly irradiated LiF:Mg,Cu,P detectors

Well known, widely applied high sensitive thermoluminescence (TL) detector LiF:Mg,Cu,P (MCP-N) was investigated. This paper analyses changes of the TL emission spectrum of MCP-N after irradiation with ultra high doses (up to 500 kGy). Spectral dependence of TL on dose is very complex especially in the region of very high doses (>1 kGy). As a general trend we found that the number of peaks increases with dose in the long-wavelength region indicating new types of recombination centres (RCs). Wavelength peak positions for increasing doses are quite stable. Only some of them show slight red-shift.     

Features of thermoluminescence in anion-defective alumina single crystals after highdose irradiation

The effect of high-dose irradiation by electron beam with nanosecond duration and by gamma-rays on thermoluminescence (TL) yield of anion-defective dosimetric Al₂O₃:С crystals is studied. It is shown that in a wide dose range up to 10 kGy no significant changes in the TL curve shape and the temperature position of the main dosimetric peak (T = 460 K) are observed. The TL yield of this peak is in saturation in the high-dose range 5–80 kGy. Then anomalous increase in TL yield is registered at the dose growth up to 800 kGy. With that an intensive band appears in the green spectrum region in the photoluminescence spectrum. The role of aggregate defects forming F₂-type centers with the increase of TL yield in Al₂O₃:С crystals under high-dose irradiation is discussed.     

Evaluating the influence of experimental conditions on the photon energy response of Al2O3:C optically stimulated luminescence detectors

This work presents a determination of the photon energy response of Al₂O₃:C optically stimulated luminescence (OSL) detectors (single crystals and Luxel^® detectors) to photons with mean energies from 10 keV to 1225 keV. Irradiations were performed free-in-air using standard X-ray fields (narrow-spectrum series) specified by the International Organization for Standardization. The OSL readouts were conducted under different conditions (e.g., different optical filters; continuous or pulsed stimulation) and the analyses were performed using the initial OSL intensity or total OSL area. The measured photon energy response of the OSL signal was compared to the ratio between the mass–energy absorption coefficient for Al₂O₃:C and air. The results demonstrate that the photon energy response of Al₂O₃:C is not only dependent on the energy deposited, but also on the experimental conditions. This is attributed to the effect of ionization density on the OSL properties of Al₂O₃:C, which affects the shape of the OSL curve and the relative intensity of the OSL emission bands. The results highlight the importance of maintaining similar OSL readout conditions and using similar types of detectors when determining and applying photon energy correction factors.     

The influence of temperature distribution in a sample on thermoluminescence glow curves

This paper deals with the analysis of thermoluminescence glow curves when the distributions of temperature and concentration of trapping centers in a sample are taken into account. A check on NaClMgCl₂ confirms the theoretical model.We wish to thank Dr. A.Bohun, DrSc. for his kind guidance and advice given to us during our work on this paper.     

光伏型光电探测器的激光软损伤机制

对激光辐照功率密度高于探测器饱和阈值而低于其破坏阈值（中等功率的激光）时光伏型光电探测器的软损伤进行了理论研究,提出了一种新机制。当激光辐照功率密度超过探测器的饱和阈值以后,载流子的带间跃迁达到深度饱和,在半导体内产生热载流子且热载流子的温度高于晶格的温度,从而导致了光伏型光电探测器的电压输出信号随着辐照光功率密度的增加而下降直到零压输出的现象。对激光辐照下光伏型HgCdTe探测器的输出信号进行了模拟计算,结果表明,辐照光功率密度处于一定范围内探测器的输出信号随着辐照光功率密度的增加而逐步下降,甚至接近于零,与实验结果相符合。     

光伏型光电探测器的激光软损伤机制

 对激光辐照功率密度高于探测器饱和阈值而低于其破坏阈值（中等功率的激光）时光伏型光电探测器的软损伤进行了理论研究,提出了一种新机制。当激光辐照功率密度超过探测器的饱和阈值以后,载流子的带间跃迁达到深度饱和,在半导体内产生热载流子且热载流子的温度高于晶格的温度,从而导致了光伏型光电探测器的电压输出信号随着辐照光功率密度的增加而下降直到零压输出的现象。对激光辐照下光伏型HgCdTe探测器的输出信号进行了模拟计算,结果表明,辐照光功率密度处于一定范围内探测器的输出信号随着辐照光功率密度的增加而逐步下降,甚至接近于零,与实验结果相符合。     

Total fluence influence on the detected magnitude of neutron burst using proportional detectors

The measurement of very short neutron bursts, when individual neutrons cannot be counted in the usual manner, is possible with proportional detectors (such as ³He) taking the integration of the total electric charge due to many overlapped interactions, as the measure of the amount of the neutron signal. This method requires a correction related to the total amount of neutrons that interacted with the detector. This correction originates in the well-known build-up of positive electric charge too slow to be dislodged from the detection volume during the neutron burst. This causes self-shielding of the applied electric field with the ensuing reduction of the charge multiplication process in the gas, described in the literature.Short neutron bursts from a plasma focus device and a conventional isotopic neutron source were employed in the experimental phase and the known theory was applied in the analysis, which justifies assigning the observed effects to the space-charge shielding of the externally applied electric field.This work introduces a correction to the neutron yield derived from the registered electric charge, through a model of collected charge reduction as a function of total neutrons measured.     

Effect of gamma irradiation on thermoluminescence and thermodynamic parameters of LiKSO4 doped with Nd2 O3

Abstract

The thermoluminescence and thermo-dynamic parameters of LiKSO₄: Nd were investigated. The effect of Nd dopant concentration in the range 0.1-1% as well as that of γ-irradiation dose in the range 56.3-3.24 × 10⁵ Gy were studied. The glow curves of the material are characterized by a double peak; each behaving seperately with radiation dose. The highest TL enhancement was obtained for Nd concentration of 0.5%; while irradiation dose of few hundreds Gy gave the best TL response. The thermodynamic parameters of LiKSO₄ doped with 0.5% Nd decreased with radiation dose up to about 5000 Gy.     

The influence of neutron and proton irradiation on the magnetization of biotite

This paper reports on the results of investigations into the field dependences of the magnetization for biotite in the initial state, after heat treatment at a temperature of 1000°C for 15 min, and after irradiation with 14-MeV neutrons at a dose of 1.2×10¹³ cm^?2 or with 3-MeV protons at a dose of 2.2×10¹⁴ cm^?2. It is demonstrated that the magnetization of biotite drastically increases after neutron and proton irradiation. This effect can be associated with the formation of oxide melt at radiation-induced thermal peaks and the freezing of high-temperature phase states corresponding to magnetite or magnetite-hematite solid solutions.     

Effect of ion irradiation on the thermoluminescence properties of K2Ca2(SO4)3 phosphor

This paper presents the thermoluminescence (TL) studies of ion-irradiated potassium–calcium mixed sulfate phosphor. The sample was prepared by the solid-state diffusion method. The X-ray diffraction study of the prepared sample suggests an orthorhombic structure with an average particle size of 0.16 μ m. The samples were irradiated with 1.2 MeV argon ions at fluences varying between 10¹¹ and 10¹⁵ ions/cm². The argon ions penetrate to a depth of 1.93 μ m and lose their energy mainly via electronic stopping. Due to ion irradiation, a large number of defects such as oxygen vacancies, radicals and color centers are formed in the sample. TL glow curves were recorded for each of the ion fluences. A linear increase in the intensity of TL glow peaks was found with an increase in the ion dose from 72 kGy to 720 MGy. The kinetic parameters associated with the prominent glow peaks were calculated using glow curve deconvolution, different glow curve shapes and sample heating rate methods.     

高剂量X射线辐照下碲锌镉探测器的深度极化效应

采用双向辐照的方法研究了碲锌镉晶体中的深度极化效应,实验结果表明,深度极化效应与直接辐照的X射线剂量无关。通过对晶体内电场分布的模拟,进一步分析了深度极化的形成机制,认为深度极化效应与极化效应一样,都是由于高浓度的堆积电荷使得晶体内电势畸变从而阳极不能收集信号,但它与通常极化效应有所不同,造成这种极化的高浓度空间电荷是从更高浓度的空间电荷区扩散而来的,发生深度极化的区域本身并没有受到X射线的强烈辐照。     

波段外激光辐照PC型探测器的反常响应机制

提出了PC型半导体探测器对波段外激光辐照的热电子光电导响应机制。响应波段外激光辐照PC型半导体探测器时,探测器有响应且输出电压信号迅速增大,与波段内激光辐照时的响应规律截然不同,这是由光激发能带内热电子而引起的光电导现象。当较强功率的激光辐照时还应考虑热效应。依据该机制进行了模拟计算,计算结果表明当PC型HgCdTe探测器被波段外激光辐照时,热电子的产生使得电导率减小,进而导致探测器的电阻增大。