Different kinds of thermoluminescence detectors (TLDs) can provide determination of absorbed doses in different environments, including tissues of human organism. The advantage of thermoluminescent dosimeters over other ones for determination of absorbed doses of ionizing radiation (IR) lies in high sensitivity of thermoluminescent detectors to different types of radiation, in integral character of dose accumulation, small sizes, and quite low cost price. Based on the above, one can conclude that TLDs can be effectively used for studying the real topography of radiation fields, for medical application of ionizing radiation and for radioecological monitoring of territories while controlling radiation effects in the environment. In dosimetry, the most widespread thermolumines- cent detectors among the staff who work with IR [6-8] are the ones based on LiF. This is due to the affinity between the effective atomic number of LiF on photoemission (Zeff - 8.65) and the effective atomic number of the human soft tissue (Zeff - 7.8). Substances with identical effective index numbers Z have comparable mass attenuation coefficients μ/ρ, where μ is the linear absorption coefficient, cm-1, ρ is the density, g/cm3. For photon absorption radiation IR is described by the following equation [1, 3, 13]: N = N 0 e -m l = N 0 e- ( m / r ) rl (1) Where N0 - is the number of g-quanta, included in absorber layer, N is the number of g-quanta, passed through the absorber, g/cm3, m/ρ is the mass absorption coefficient, cm2/g, l is the absorber layer thickness, cm, rl is the layer thickness, g/cm2. The mass absorption coefficient values of different substances are close for high-energy radiation and varied widely for low-energy photon radiation. For high- energy radiation, absorption is determined mainly by the absorber thickness, g/cm2, whereas for low-energy g-quanta absorber composition is of crucial importance. This is demonstrated in dependence of thermoluminescence on IR energy, especially in the area of photoelectric emission, i.e. in gamma impact energies lower than 200 keV. Fig. 1 shows the dependence of the mass absorption coefficients on the gamma-quanta energy for some materials [1]. Please cite this article in press as: Aluker N.L., Suzdaltseva, Ya.M., Herrmann M.E., Dulepova A.S. Thermoluminescent detectors for surveillance studies of radiation exposure of the population. Science Evolution, 2016, vol. 1, no. 2, pp. 3-10. doi: 10.21603/2500-1418-2016-1-2-3-10. Copyright © 2016, KemSU. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license. This article is published with open access at http:// science- evolution.ru/ μ /ρ, cm /g μ /ρ, cm /g 2 2 0.1 Eγ, keV Fig. 1. Dependence of the mass absorption coefficients on the gamma-quanta energy for some materials [1]. Fig. 2. Energy dependences of the thermoluminescence yield on a logarithmic scale (with reference to 60Co) for different types of detectors [14]. Fig. 2 shows the energy dependences of the thermoluminescence yield on a logarithmic scale with reference to 60Co for detectors based on different luminophors. The X-axis is the energy; the Y-axis is the relative yield of TL-IЕ/ICo-60 Despite the undoubted merit (equivalence of human soft tissues), detectors made of LiF-based materials, used in personal dosimetry, have a number of significant disadvantages (spread in sensitivity within the lot, a number of thermoluminescence peaks, a complex multi- step heating mode, dose dependence superlinearity at doses of 0.1 Gy, hygroscopicity) [6, 7]. Currently, the range of materials used to produce these detectors, has expanded considerably. Depending on the dosimetry problem, it is expedient to apply the most appropriate type of detector (luminophor). In addition to LiF, fundamentally different classes of substances are currently considered as radiation- sensitive environments, the most important of which are wide-band oxide materials such as Al2 O3 , BeO, MgO, SiO2, and others [8-11, 13]. If you want to study the topography of radiation fields, used, for example, for exposure of semiconductor or ceramic components, it is advisable to use detectors with effective atomic number and element composition as close as possible to the irradiated material [14, 15]. i i If a luminophor has multiple traps in different depths (Е ), TL curve will have some peaks. Various thermoluminescence peaks may have different yield of luminescence, i.e., different probability of photon emission upon recombination, different luminescence spectral composition, which may lead to different luminescence registration efficiencies depending on the spectral sensitivity of the photodetector used. In this regard luminophors having single peak thermoluminescence curve, for example, α-Al O , SiO 2 3 2 (Fig. 3) have clear advantages over luminophors with a complex thermoluminescence curve, for example, LiF: Mg, Ti [13] (Fig. 4). However, single-peaked shape of the thermolumi- nescence curve does not indicate that recombination after the charge carriers release from a trap is carried out at one of the luminescence center, but indicates only that the charge carriers are released from the trap of a certain depth (Е ). The luminescence spectrum may have some bands asisociated with the recombination of carriers at different impurity or structural defects - luminescence centers. Experimental Part. Comparison of characteristics of different types of detectors Thermoluminescent method of dosimetry is used in 90% of all cases of individual radiation control of personnel working in contact with ionization sources worldwide. The advantages of thermoluminescent detectors (TLDs) are: high sensitivity to different types of radiation, integral accumulation of radiation doze, small dimensions and relatively low cost. Due to the small size of TLD, these detectors can be used to detect real topography of ionization fields, including medical application of ionization radiation, as well as for radioecology monitoring of areas exposed to radiation. It is necessary to use exactly the same dosimetric equipment and experimental conditions, and to compare results between the different types of detectors, to be Thermoluminescence Thermoluminescence 120 100 80 60 40 20 0 360 380 400 420 440 460 480 500 520 Temperature, K Fig. 3. Thermoluminescence curve of TLD-K detector (SiO2) at a heating rate of 2°С/sec (a). Fig. 4. Thermoluminescence curve of LiF: Mg, Ti under irradiation by 90Sr/90Y, dose 0.1 Gy, heating rate 1°С/sec (b). able to measure the advantages and disadvantages of different types of detectors. This work has used a modified dosimetric installation DTU-01M. The dosimetric characteristics of various thermoluminescent detectors (made from various materials by differentmanufacturers) weretestedandcomparedduring experiment. A range of detectors was tested, including LiF (USA), LiF (Stavropol, Russian Federation), LiF (China), TLD-100 (LiF, Irkutsk, Russian Federation), TLD-К (SiO2 Kemerovo, Russian Federation), TLD- 500 (Al2O3 ) (Sverdlovsk, Russian Federation), Ca3F, Table 1. Main parameters of the detectors used CaSO and detectors based on the silicon oxide mixed with nanodispersed diamonds (TLD-KAS (SiO 2, С)). TLD-KAS is a synthesized test prototype based on a 4 4 heterogeneous material composed of a luminophor with high luminescence yield, and diamond nanoparticles (varying the percentage of diamond nanoparticles results in variation of Zeff of the detector). A study of dosimetric characteristics was carried out. The test of the experimental material has demonstrated that the addition of diamond particles significantly increases the sensitivity range of the detector, which is important for industrial dosimetry. During the experimental work, the dimensions and volume of detectors were calculated. Slope coefficients of linear dependence on the radiation dose, and sensitivity of detectors and materials were calculated with reference to the DTG-04 detector (relative coefficients taking into account the volume of detector). Table 1 shows the main parameters (appearance, dimensions, peak temperature) of the detectors examined. Table 2 shows relative characteristics of different types of detectors based on different materials (LiF, Al2O3, SiO2 CaF2 CaSO4). Table 3 summarizes some characteristics of the detectors and conditions of their annealing and measurements (experimental and literature data). Table 4 shows literature data for sensitivity of some LiF-based detectors under various irradiation conditions TLD-K detectors have relatively wide detection range. Detector type Diameter, mm Thickness, mm Volume, mm3 Peak temperature, °С Appearance LiF (USA) 4.66 0.73 12.37 207 Non-transparent polycrystalline disk LiF (Stavropol, Russian Federation) 4.41 0.95 14.6 200 Non-transparent polycrystalline disk LiF (China) 4.58 0.75 12.2 200 Non-transparent polycrystalline disk LiF (Irkutsk, Russian Federation) 4.57 0.94 15.3 203 Transparent crystalline disk TLD-K(SiO2) 2.78 0.51 3.9 132 Semi transparent amorphous square TLD-500 (Al2O3 ) 5.04 0.85 17.0 171 Transparent crystalline disk CaF2 5.01 1.01 20.0 346 Non-transparent polycrystalline disk CaSO4 5.08 1.02 20.7 215 Non-transparent polycrystalline disk TLD-KAS (SiO2, С) 4.23 0.9 12.5 168 Non-transparent polycrystalline disk Table 2.Comparative characteristics of detectors Type Material Diameter Thickness V, mm3 Relative sensitivity coefficient (with reference to DTG-04) Relative coefficient (with reference to DTG-04) USA LiF 4.7 0.7 12 0.3 0.4 Stavropol LiF 4.4 1.0 15 0.3 0.3 China LiF 4.7 0.7 13 0.3 0.3 DTG-04 Irkutsk LiF 4.6 0.9 15 1.0 1.0 Kemerovo TLD-K SiO2 2.9 0.5 4 0.8 2.7 Ekaterinburg TLD-500 Al2O3 5.0 1.0 19 32 29 CaF2 CaF2 5.0 1.0 20 6 5 Tartu CaSO4 CaSO4 5.1 1.0 21 13 10 TLD-KAS SiO2 +С 4.2 0.9 13 0.03 0.03 Table 3. Characteristics of the detectors and conditions of their annealing and measurements (experimental and literature data) Detector type Material Annealing conditions Measurement conditions Dose equivalent mSv Repeatability, % Within-lot variation % ТLD-100 LiF - Mg, Ti 60 min at Т 400°С Prior heating to 100°С 0.042±0.008 4 23 ТLD-400 LiF - Mg, Ti 60 min at Т 400°С Prior heating to 100°С 0.040±0.004 5 27 DTG-4 LiF - Mg, Ti 60 min at Т 400°С Prior heating to 100°С 0.039±0.004 4 20 ТLD-1011 LiF - Mg, Cu, P 10 min at Т 240°С Prior heating to 60°С, 10 sec 0.004±0.002 6 24 TLD-500К Intrinsic defects Annealing at 400°С Linear heating