Alkali hallde thermoluminescent dosimeters

Single crystals of KCl: Ca have been studied as thermoluminescent dosimeters for the measurement of X-radiations from Cu and Mo targets in the range of 5 mR to 50000 R. Depending upon the amount of radiations received by these crystals, thermoluminescence peaks at 85°, 35° and 190°C are observed for a heating rate of 40°C/min. The total area under the thermoluminescence curve is observed to be directly proportional to the amount of radiations received by these crystals. The effect of the lag of time between the exposure to radiations and the heating for thermoluminescence has also been studied.     

Thermoluminescence and optical studies on X-irradiated terbium-doped potassium bromide crystals

This paper reports the thermoluminescence (TL) and other optical studies made on terbium-doped KBr crystals X-irradiated at room temperature. Photoluminescence studies confirm the presence of terbium ions in the KBr matrix in their trivalent form. Formation of Z₁ centres on F-bleaching of X-irradiated crystals is observed. The characteristic emission due to Tb³⁺ ions in the spectral distribution under optically stimulated emission and thermoluminescence emission confirm the participation of the Tb ions in the recombination process. TL process has been identified to be due to the thermal mobilization of electrons produced during the colouration process.     

Mechanism of formation of nonlinearity in the dose dependence of the thermoluminescence output for anion-defect α-Al2O3 crystals

The mechanism of formation of nonlinearity in the dose dependence of the thermoluminescence output was investigated for anion-defect α-Al₂O₃ single crystals. The experiments revealed a new specific feature: the nonlinearity of the dose dependence of the thermoluminescence output depends on the heating rate of crystals during recording of thermoluminescence. It was established that this effect and other thermoluminescence features studied earlier for anion-defect α-Al₂O₃ crystals are adequately described in the framework of a unified mechanism associated with the interactive interaction of dosimetric and deep traps. Recommendations are given for a decrease in the range of the superlinear portion in the dose dependence of the thermoluminescence output for the crystals under investigation.     

Specific features of luminescence of radiation-colored α-Al2O3 single crystals

Results of a comparative study on specific features of luminescence of thermochemical and radiation-colored crystals of aluminum oxide have been described. It is shown that crystals containing oxygen vacancies of different origins have identical main optical properties. A vacancy or vacancy-impurity origin of deep traps has been assumed. Some specific features of thermoluminescence (TL), which are common for both types of crystals, such as the dependence of the TL output on the heating rate and the occupancy of deep traps described by the model of interactive trap system, have been established.     

Simulation of the superlinearity of dose characteristics of thermoluminescence of anion-defective aluminum oxide

The specific features revealed in the superlinearity of dose dependences of thermoluminescence of anion-defective aluminum oxide single crystals have been considered theoretically in terms of the model of an interactive trap system. The model explains the decrease in the degree of superlinearity at a low heating rate, as well as with an increase in the dose increment, the occupancy of deep traps, and the sensitivity of the crystals to radiation due to the increase in the concentration of luminescence centers. The obtained results indicate a widening of the possibilities of the model for interpreting experimental data in the investigation of the dose characteristics of thermoluminescence of the studied crystals.     

Molecular dynamics simulation of the interaction of low-energy Ar ions with polyethylene and pentacene surfaces

The normal bombardment of bulk polyethylene and pentacene crystals with 100-eV Ar ions has been investigated by molecular dynamics simulation using the many-body potential for covalent bonds. Polyethylene targets with and without chain folds on the surface have been used. The sputtering yield and changes in the atomic structure of targets are discussed.     

On the role of hole trapping centers in the interactive mechanism of the trap interaction in anion-defect alumina single crystals

The effect of deep hole traps on the intensity and shape of the dosimetric peak of thermoluminescence (TL) has been studied at 450 K in anion-defect alumina single crystals. It has been shown that filling of deep hole centers leads to a decrease in the sensitivity to radiation of crystals with a small half-width of the TL peak and has no effect on the sensitivity of crystals with a broadened peak. It has been assumed that traps responsible for the TL dosimetric peak broadening are of hole nature, which can be caused by the presence of Ti3+ ions in the corundum lattice. The results obtained have been interpreted within the modified model of the interactive system of traps.     

CRYSTALLIZATION OF A LOW MOLECULAR WEIGHT POLYETHYLENE AND PARAFFINS UNDER A TEMPERATURE GRADIENT

A low molecular weight polyethylene (PE) and even-number paraffins were crystallized under a temperature gradient. Highly oriented crystalline textures were developed by the temperature slope crystallization. The in situ crystallizing surface was observed by an optical microscope and X-ray diffraction. Polyethylene has a b-axis orientation in which the lamellar normal and crystalline c-axis are perpendicular to the temperature gradient. On the contrary, in the even-number paraffins, both axes are parallel to the temperature gradient. The results of the in situ measurements and the crystalline orientation are compared and discussed for both cases.     

Influence of low and high temperature annealing on the blue and green emission bands of ZnS crystals

After annealing at 350 °C, in the luminescence spectra of pure and Cu-doped ZnS crystals a reversible blue-green conversion has been obtained. The blue-green conversion of luminescence is correlated with analogous reversible variations in the optical transmission and thermoluminescence properties. Besides these low temperature results, in the fluorescence spectra of undoped ZnS crystals, which are annealed at 1,000 °C in sealed evacuated quartz ampoules, a reversible blue-blue conversion has been observed. All these effects, induced by distinct heat treatments, seem to be mainly controlled by changes in the structural disorder or/and by the evaporation of lattice atoms from the surface of the crystals.Dedicated to Prof. Dr. Dr. Ing. E.h.W. Hanle on occasion of his 75^th birthdayPart of thesis, Gießen 1974 (D26)     

Polarization of thermoluminescence of various scheelites

The polarization of the thermoluminescence of various scheelite type single crystals being correlated with the thermal decay of intrinsic hole centres has been measured. The crystals show partial z-polarization of the thermoluminescence. The degree of polarization of the glow light increases with increasing compression of the anionic XO^2-₄ complexes in different crystals. A model explaining the results on the basis of the term diagram of a single oxocomplex is presented.     

Phototransferred thermoluminescence in anion-defect α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystals

Thermally stimulated migration of charge carriers from trapping centers responsible for the main thermoluminescence peak at 450 K to a deep trap was experimentally observed in anion-defect α-Al₂O₃ crystals. Optically induced transport of carriers from the deep trap to the main trap was also observed to cause phototransferred thermoluminescence at 450 K. The results obtained experimentally confirm the adequacy of the basic assumptions made in the model of interactive interaction between main and deep traps in the crystals under study, as well as substantiate the method of repeated obtaining of dosimetric data.     

Influence of low and high temperature annealing on the blue and green emission bands of ZnS crystals

After annealing at 350 °C, in the luminescence spectra of pure and Cu-doped ZnS crystals a reversible blue-green conversion has been obtained. The blue-green conversion of luminescence is correlated with analogous reversible variations in the optical transmission and thermoluminescence properties. Besides these low temperature results, in the fluorescence spectra of undoped ZnS crystals, which are annealed at 1,000 °C in sealed evacuated quartz ampoules, a reversible blue-blue conversion has been observed. All these effects, induced by distinct heat treatments, seem to be mainly controlled by changes in the structural disorder or/and by the evaporation of lattice atoms from the surface of the crystals.     

TL properties of anhydrous CaSO4:Tm improvement

CaSO4:Tm is excellent phosphors for dosimetry of ionising radiations due to their high sensitivity, wide dose range (from 10^?6 to 1 Gy), relatively simple trap structure, good chemical, thermal and physical stability and ease of preparation. Since 1968 have been developed new methods of preparing aim to increase the sensitivity and the linearity of the CaSO₄:Tm thermoluminescence. The objective of this work is to obtain single crystals of CaSO₄:Tm under controlled crystal growth conditions, such as temperature, atmosphere and velocity, aiming to improve the TL sensitivity of the crystals and investigate its dosimetric properties in order to evaluate the applicability of this material to dosimetry.     

Investigation of the electronic structure of the BiSBr and BiSeBr clusters by density functional method

The energy levels of valence bands (VB) of the BiSBr and BiSeBr crystals have been calculated for investigation of the photoelectron emission spectra of BiSBr, BiSeBr and BiSI crystals. The molecular model of this crystal has been used for the calculation of VB by the Density Functional Theory (DFT) method. The molecular cluster, consisting of 20 molecules of BiSBr, BiSeBr, has been used for calculations of averaged total density of states, including atom vibrations. The spectra of the averaged total density of states from VB of BiSBr and BiSeBr clusters have been compared with the experimental photoelectron emission spectra from VB of BiSI crystals. The results clarify that the atomic vibrations in A⁵B⁶C⁷ type crystals with chain structure create a smoother appearance of the averaged total density of state spectrum and the experimental X-ray photoemission spectra (XPS).     

Impurity Cu+ centers in LiF single crystals

LiF single crystals with copper impurity (0.0004–0.002%) have been grown by the Czochralski method and investigated. The luminescence, excitation, and optical absorption spectra have been recorded. The luminescence spectrum contains a band at 450 nm upon 250-nm excitation. This band is attributed to Cu⁺ centers in the samples grown. The mechanisms of capture and recombination during thermoluminescence are considered.     

Effect of doping with cobalt on radioluminescence and low temperature thermoluminescence of Li2B4O7 crystals

X-ray excited emission spectra at various temperatures, as well as low temperature glow curves of Czochralski-grown Li₂B₄O₇:Co (LTB:Co) single crystals, have been recorded and compared with the data available for undoped LTB and LTB:Eu,Mn. Although the presence of cobalt does not influence the radioluminescence of the material, it clearly alters its thermoluminescence; specifically, the number of peaks in the glow curve of LTB:Co is reduced as against that of LTB and LTB:Eu,Mn. This observation and its possible interpretations shed new light on the issue of shallow traps in lithium tetraborate crystals.     

低温燃烧合成法制备的氧化铝陶瓷粉体的发光特性

α-Al₂O₃∶C单晶具有优良的热释光特性,被用做热释光剂量计,但α-Al₂O₃∶C晶体剂量计的形状不易加工,生产成本高且碳在晶体中难以掺杂均匀。采用低温燃烧合成法以无水乙醇为溶剂,尿素为染料,硝酸铝为反应物制备少团簇、分散均匀的片状α-Al₂O₃∶C陶瓷粉体。探讨不同点火温度和不同退火温度对其光致发光特性的影响,不同退火温度对热释光特性的影响以及热释光与辐射剂量(90Sr β)的关系。通过分析α-Al₂O₃∶C陶瓷粉体的光致发光光谱得出：α-Al₂O₃∶C陶瓷粉体的发射波长在395 nm附近,点火温度T≤800℃时,点火温度为500 ℃制备的α-Al₂O₃∶C陶瓷粉体的光致发光强度最强;在相同点火温度T=500 ℃下,经不同温度退火制备α-Al₂O₃∶C陶瓷粉体,点火温度为500 ℃制备的α-Al₂O₃∶C陶瓷粉体经1 000 ℃退火后光致发光强度最强。通过分析α-Al₂O₃∶C陶瓷粉体的热释光曲线得出：退火后的α-Al₂O₃∶C陶瓷粉体在200 ℃左右的热释光峰值占主导,900 ℃退火的α-Al₂O₃∶C陶瓷粉体在200 ℃附近的热释光峰值最强;通过峰高法对900 ℃高温退火处理后的α-Al₂O₃∶C陶瓷粉体位于200 ℃左右的热释光峰做剂量响应曲线,可以看出,在1～50 Gy剂量范围内具有良好的热释光剂量线性响应关系,在50～200 Gy剂量范围内出现超线性响应关系。与α-Al₂O₃∶C晶体(1～10 Gy)和多孔Al₂O₃∶C薄膜(1～10 Gy)相比,α-Al₂O₃∶C陶瓷粉体的线性剂量响应范围明显扩大。此研究可为提高氧化铝陶瓷粉体的热释光性能提供思路。     

Colored LiF: an optical material for all seasons

Colored LiF salt has been always considered a singular optical material among alkali halides and other dielectric crystals for its peculiar characteristics, which in due time have been applied with success in thermoluminescence and laser technology. Lately, while the two previous topics have been revived, new relevant results have been obtained in the optoelectronic field by using both bulk crystals and newly characterized thin films. In practice, miniaturized photoluminescent patterns can be produced rather easily by using low-energy electron beams and soft X-rays. So, LiF salt is becoming a new interesting photonic material with promising developments in basic reasearch and applications as well.     

Thermoluniscence of x-ray damaged NH4Cl crystals

A relatively intense thermoluminescence peak has been observed at about 245 K in X-irradiated HH₄Cl crystals. This peak is correlated with the optical absorption properties of the crystals and is ascribed to thermal destruction of V_k centres. Various models of the thermoluminescence processes are compared with experimental glow curves, and the parameters giving the best fit to experimental results are reported.     

Photostimulated thermoluminescence of x-irradiated NaCl

The thermoluminescence and photostimulated thermoluminescence of X-ray coloured NaCl crystals has been studied, together with the thermal annealing of F, F′ and M centres. Three glow peaks centred at 315, 341 and 348°K are obtained in the temperature range 300–400°K. The first peak (315°K) is ascribed to electron trapping by Cu²⁺ centres formed by X-irradiation. The other peaks (314 and 348°K) are related to the thermal annealing of M and F centres, respectively.