Gamma radiation induced sensitization and photo-transfer in Mg2SiO4: Tb TLD phosphor

doi:10.1016/0029-554X(79)90691-8

Nuclear Instruments and Methods

Volume 159, Issues 2–3, 15 February 1979, Pages 585-592

https://doi.org/10.1016/0029-554X(79)90691-8 Get rights and content

Abstract

Mg₂SiO₄: Tb TLD phosphor was found to show enhanced TL sensitivity to both gamma and UV radiations after high pre-gamma exposures (>100 R) and a post-annealing treatment at 300°C for 1 h. Maximum sensitization factors of 2.8 and 55 were obtained at the pre-exposure levels of 5.2×10¹ C/kg and 1.3×10³ C/kg for gamma and UV test radiations respectively. The near constancy of the intensity of the residual TL (RTL) peak at 500°C for the sensitized sample with increasing test-gamma exposures has ruled out the re-trapping model proposed earlier for the gamma radiation induced sensitization in this phosphor. The T_max for the sensitized phosphor was found to occur at a higher temperature compared to that for the virgin phosphor. The dependence of sensitization on RTL was explained qualitatively on the basis of competition between sensitization traps (having higher energy than the dosimetry traps) and RTL traps while capturing the charge carriers generated during the test-gamma exposure.

The sensitization observed in this phosphor to UV test radiation was found to be a consequence of the photo-transfer of charge carriers from deep (RTL) traps to the shallow (dosimetry) traps. The reduction in RTL peak (500°C) intensity of the sensitized sample with increasing test-UV exposure has demonstrated the photo-transfer mechanism in this phosphor.

The TL response of the virgin Mg₂SiO₄: Tb phosphor was found to be supralinear to both gamma and UV radiations. The TL response of the sensitized phosphor was found to be linear to gamma radiation and sublinear to UV radiation.

References (8)

A.R. Lakshmanan et al.
Nucl. Instr. and Meth.
(1978)
T. Hashizume et al.
K. Ayyangar et al.
Phys. Med. Biol.
(1974)
T. Nakajima

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The material is mostly formed of relatively light elements and its effective atomic number is approximately 11 so that it is very suitable for the environmental and personnel monitoring [5]. Thermoluminescence studies on Mg2SiO4: Tb have been carried out by several groups [6–12]. It was noticed that although it has high response to the radiation, TL properties of Mg2SiO4: Tb are not very stable and critically influenced by the preparation method [13].
Magnesium orthosilicate doped with terbium (Mg₂SiO₄:Tb) has been reported as the most efficient thermoluminescence dosimeter material. The results of this paper indicate that further sensitivity improvements of this material are achievable by co-doping with Na⁺ ions. The main peak of the thermoluminescence is enhanced three times with the addition of sodium ions. The optimized concentration of Na⁺ is 11 mol% which is much higher than the expectation for the role of a trace element dopant. The results suggest that the addition of sodium ions may not only remove the charge unbalance problem and enhance the emission intensity, but also play an important role in defining and stabilizing the defect structures.
Morphology and thermoluminescence properties of terbium doped magnesium orthosilicate
2017, Radiation Measurements
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Thus it has a potential as a candidate material for the environmental and personal monitoring. Several studies have already been carried out on the dosimetry properties of Mg2SiO4: Tb (Nakajima, 1972; Mittani et al., 2008; Lakshmanan and Vohra, 1979; Bacci and Furetta, 1992; Prokic and Yukihara, 2008). The response of Mg2SiO4: Tb with different irradiation sources has been revealed and the appearance of a 220 °C glow was seen only after laser irradiation (Miyoshi et al., 2004).
The morphology and structural form of Tb doped magnesium silicate are reported as a function of the dopant concentration of Tb. The preparation method is described. This includes a sintering step which is time sensitive and an optimum processing time is discussed to improve dosimeter sensitivity. The thermoluminescence spectra are remarkable as they reveal peak shifts in the temperature of the characteristic lines of the Tb dopant. A model related to charge capture by different upper state orbitals of the rare earth transitions is offered. Optically stimulated luminescence data are also included.
Thermoluminescence, OSL and defect centers in Tb doped magnesium orthosilicate phosphor
2016, Applied Radiation and Isotopes
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They reported that among all the rare earth doped LMB samples, Tb3+ doped sample yielded the highest TL intensity. Among the Tb ion activated phosphors, magnesium orthosilicate is one of the most sensitive phosphors exhibiting high gamma sensitivity with TL sensitivity more than 40 times and reaching 100 times than that of LiF TLD −100 (LiF: Mg, Ti) (Hashizume et al., 1971; Toryu et al., 1973; Ayyangar et al., 1974; Sun and Becker, 1975; Bhasin et al., 1976; Lakshmanan and Vohra, 1979; Prokic and Yukihara, 2008; Wang et al., 2014; Mittani et al., 2008). The phosphor has other advantages like a linear dose range extending from 5×10−6 Gy to 3 Gy, low fading over long duration of time (3% over two months time duration for gamma irradiation), a simple annealing procedure (500 °C for half an hour), high thermal and chemical stability.
Mg₂SiO₄:Tb phosphor exhibits four thermoluminescence (TL) peaks at 124, 244, 300 and 370 °C for a heating rate of 2 °C/s, 244 °C peak being the main dosimetry peak. The irradiated phosphor exhibits CW-OSL response on stimulation with blue (470 nm) light. Thermal decay of OSL shows that all the TL traps contribute to CW-OSL signal. Its TL and OSL sensitivities are 0.21 and 0.038, respectively, than that of Al₂O₃:C (Landauer Inc.). Its CW-OSL response increases linearly up to 30 Gy, thereafter increase was supralinear up to the studied dose of 1000 Gy. Electron Spin Resonance (ESR) studies were carried out to study the defect centers induced in the phosphor by gamma irradiation and also to identify the centers responsible for the TL process. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least three distinct centers. One of the centers (center I) with an isotropic g-factor 2.0122 is attributable to an intrinsic O^- radical and this correlates with the main TL peak at 244 °C. Center II with an isotropic g-factor 2.0012 is assigned to an F⁺-center (singly ionized oxygen vacancy) and is the likely recombination center for all the TL peaks. Both the centers grow with radiation dose at least up to 1 kGy. Center III with an axial symmetric g-tensor with principal g-values g_||=2.0049 and g_⊥=2.0029 is identified as an F⁺-center and is not related to the observed TL peaks in the phosphor.
Superlinear dose response of thermoluminescence (TL) and optically stimulated luminescence (OSL) signals in luminescence materials: An analytical approach
2012, Journal of Luminescence
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When this behavior takes place in a certain dose range, a plot of L as a function of D on a log–log scale is expected to yield a straight line with a slope of k. Superlinear dose dependence of the TL signal has been reported in semiconducting diamonds [1], CaF2:Tb4O7 [2], Mg2SiO4:Tb [3,4], for several TL peaks in quartz ([5–8]), LiF:Mg,Ti ([9–12]), NaCl:Mg and KCl [13], fused silica [14], Mg2SiO4:Tb [15], and carbon doped Y3Al5O12 (YAG:C) [16]. There have also been several reports of superlinear dose dependence of OSL signal in quartz and mixed feldspars [17], quartz samples [18], annealed quartz samples from bricks [19], and in Al2O3:C [20].
The phenomenon of superlinear dose response of thermoluminescence (TL) and optically stimulated luminescence (OSL) signals has been reported for several important dosimetric materials. We develop new analytical equations for the filling of traps and centers during irradiation and for the read-out stage of annealed luminescence materials, within the context of a two-trap and two-center model. The equations are applicable for both TL and OSL signals in annealed dosimetric materials, and are derived under the assumptions of low irradiation doses and dominant strong retrapping (weak recombination) processes. For low doses all traps and centers display linear dose response, which leads to quadratic dose response of the integrated TL/OSL signals. A new analytical expression is presented for this well-known quadratic dose dependence, in terms of the kinetic parameters in the model. The effect of elevated irradiation temperature on the integrated TL/OSL signals is also considered, and analytical expressions are obtained for this situation as well. A new type of dose-rate effect is reported based on the modeling results, which is due to irradiation during elevated temperatures. The accuracy of the analytical expressions is verified by comparing with the results of numerical simulations.
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2006, Microdosimetric Response of Physical and Biological Systems to Low- and High-LET Radiations: Theory and Applications to Dosimetry
This chapter discusses dose dependence of thermoluminescence (TL) and optically stimulated luminescence with uniform excitation. An ideal dose behavior for dosimetry and dating is a linear dependence in a broad range of doses. The TL dose dependence of β -irradiated quartz is described in the chapter. The dose dependence curve is linear in a broad range, excluding the lowest doses where the TL starts increasing at a small rate with the dose, and the rate increases gradually until it reaches a steady value, which prevails over a broad dose range. The dose dependence function of thermoluminescence (TL) is normally an increasing function, which, ideally, starts linearly and then goes sublinear when the TL maximum intensity approaches a saturation value. It is found that for the applications in dosimetry and archaeological and geological dating, linear dose dependence is desirable because the determination of the unknown dose imparted is simplified under these circumstances. It is observed that at high doses of excitation, the dose dependence behavior is usually of approaching saturation. It is suggested that the measured TL following excitation for a given set of trapping parameters within the present model depends on the competition processes during both the excitation and the heating of the sample.
Supralinearity and sensitization factors in thermoluminescence
1994, Radiation Measurements
Supralinearity and pre-dose sensitization are two characteristics of thermoluminescence (TL) glow peaks which are seen together in many of the TL phosphors. In this paper, theoretical expressions are derived for the supralinearity and pre-dose sensitization factors, based on the interactive trap system model. A new term called sensitization factor (S_nF) is introduced, which differs from the pre-dose sensitization factor (PDSF) but is related directly to the supralinearity factor (SF). The factors SF and S_nF coincide in the low and medium dose range. At high doses the latter departs considerably from the former. The case of LiF TLD-100 is used to demonstrate the application of the theory to actual experimental results.

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Gamma radiation induced sensitization and photo-transfer in Mg2SiO4: Tb TLD phosphor

Abstract

Nucl. Instr. and Meth.

Phys. Med. Biol.

Gamma radiation induced sensitization and photo-transfer in Mg₂SiO₄: Tb TLD phosphor