Dose dependence of thermoluminescence peaks (original) (raw)
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Non-monotonic dose dependence of thermoluminescence
Radiation Protection Dosimetry, 2006
The thermoluminescence (TL) intensity in different materials is usually a monotonic increasing function of the dose, which quite often reaches a saturation value. In several materials, however, non-monotonic dose dependence has been observed. The TL intensity reached a maximum at a certain dose and decreased at higher ones. Some authors refer to this effect as 'radiation damage'. In the present work, we show that the non-monotonic dependence can easily be demonstrated to result from competition between transitions model with two trapping states and two kinds of recombination centres. Two kinds of competition are considered. One in which competition during excitation dominates, the filling of the active luminescence centre is non-monotonic, and the resulting TL is non-monotonic. In the other, the filling of traps and centres is monotonically increasing, but the competition during heating causes TL intensity to reach a maximum and decline at higher doses.
Radiation Measurements, 2009
In the use of thermoluminescence (TL) and optically stimulated luminescence (OSL) for dosimetry and for geological and archaeological dating, the nature of the dose dependence of the luminescence signal is of great importance. Non-linear dependence has been shown to result either from non-linear filling of the relevant traps or recombination centers during excitation, or by a combined effect of the linear filling of traps and centers due to processes taking place during the read-out stage. Sublinearity, which had been found in several materials, was usually attributed to saturation effects during excitation of either the relevant traps or centers. Sometimes, the competition effects during the excitation between traps result in superlinearity of some TL peaks and sublinearity of others. In the present work, we show that sublinear dose dependence may take place even in the simplest possible case of one trap-one recombination center (OTOR), even when the traps and centers are far from saturation. Analytical derivations as well as simulations consisting of the numerical solution of the relevant sets of coupled differential equations show the occurrence of the sublinear dose dependence under these circumstances. The filling of the traps is shown to behave like D 1/2 where D is the excitation dose, for an appropriate choice of the trapping parameters. This, in turn, may result in a similar dose dependence of the TL and OSL signals.
A model for non-monotonic dose dependence of thermoluminescence (TL)
Journal of Physics: Condensed Matter, 2005
In the applications of thermoluminescence (TL) in dosimetry and archaeological and geological dating, a desirable dose dependence of TL intensity is a monotonically increasing function, preferably linear. It is well known that in many dosimetric materials, nonlinear dependence is observed. This may include a superlinear dependence at low doses and/or sublinear dose dependence at higher doses, where the TL intensity approaches saturation. In quite a number of materials, non-monotonic dose dependence has been observed, namely, the TL intensity reached a maximum value at a certain dose and decreased at higher doses. This effect is sometimes ascribed to 'radiation damage' in the literature. In the present work we show, both quasi-analytically and by using numerical simulation, that such dose dependence may result from a simple energy level scheme of at least one kind of trapping state and two kinds of recombination centres. One does not necessarily have to assume a destruction of trapping states or recombination centres at high doses. Instead, the main concept involved is that of competition which takes place both at the excitation stage and the readout stage during the heating of the sample. This may explain the fact that the phenomenon in question, although very often ignored, is rather common. Cases are identified in which competition during excitation dominates, and others in which competition during read-out dominates.
A model for dose-rate dependence of thermoluminescence intensity
Journal of Physics D: Applied Physics, 2000
In the applications of thermoluminescence (TL) in dosimetry and archaeological dating, it is usually assumed that the measured TL depends on the total dose applied and it is independent of the dose rate. Thus, calibration of a TL specimen is usually performed at a significantly higher dose rate than that of the dose to be determined. A few experimental accounts in the literature report on dose-rate dependences of TL intensity for a given total dose. One theoretical work published gave a numerical solution of the simultaneous differential equations governing the filling of traps and centres at different dose rates. In the present work, the numerical solution is extended so that it includes the other important stage of TL, namely the heating phase. It is shown that with a rather simple model of one trapping state and two kinds of recombination centres, dose-rate effects may occur. An appropriate choice of the relevant parameters indeed yields one emission, which increases with increasing dose rate, whereas another emission decreases with the dose rate with a constant total dose, in agreement with an experimental result in quartz quoted in the literature.
Dose-rate dependence of thermoluminescence response
1980
In the applications of thermoluminescence (TL) in dosimetry and archaeological dating, it is usually assumed that the measured TL depends on the total dose applied and it is independent of the dose rate. Thus, calibration of a TL specimen is usually performed at a significantly higher dose rate than that of the dose to be determined. A few experimental accounts in the literature report on dose-rate dependences of TL intensity for a given total dose. One theoretical work published gave a numerical solution of the simultaneous differential equations governing the filling of traps and centres at different dose rates. In the present work, the numerical solution is extended so that it includes the other important stage of TL, namely the heating phase. It is shown that with a rather simple model of one trapping state and two kinds of recombination centres, dose-rate effects may occur. An appropriate choice of the relevant parameters indeed yields one emission, which increases with increasing dose rate, whereas another emission decreases with the dose rate with a constant total dose, in agreement with an experimental result in quartz quoted in the literature.
Supralinearity and sensitization factors in thermoluminescence
Radiation Measurements, 1994
Supralinearity and pre-dose sensitization arc 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,F) is introduced, which differs from the pre-dose sensitization factor (P&SF) but is related directly to the supralinearity factor (SF). The factors SF and S, F 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.
Radiation Measurements, 1999
This paper shows the limitation of general order peak ®tting and peak shape methods for determining the activation energy of the thermoluminescence glow peaks in the cases in which retrapping probability is much higher than the recombination probability and the traps are ®lled up to near saturation level. Right values can be obtained when the trap occupancy is reduced by using small doses or by post-irradiation partial bleaching. This limitation in the application of these methods has not been indicated earlier. In view of the unknown nature of kinetics in the experimental samples, it is recommended that these methods of activation energy determination should be applied only at doses well below the saturation dose. #
High sensitivity thermoluminescence dosimetry
2001
This paper reviews the physics of the phenomenon of thermoluminescence (TL) related to dosimetric applications. Basic concepts are given using the simple model of one trap±one recombination centre. General characteristics of thermoluminescence dosimetry (TLD) materials are reviewed. Two high sensitivity TL materials are discussed in detail namely LiF:Mg, Cu, P and a-Al 2 O 3 :C. What is understood and what knowledge is still lacking of the TL mechanism in both materials is indicated. Field measurements show that in spite of incomplete understanding of the TL mechanism, both materials can be used to measure very low doses in a reliable way. Ó
2001
When thermoluminescence (TL) and optically stimulated luminescence (OSL) are utilized for dosimetry and for dating of archaeological and geological samples, one hopes that the dependence of the measured signal on the dose is linear, and that no dose-rate e ects occur. In TL measurements, however, several cases of superlinear dose dependence have been reported and also some dose-rate e ects have been found. It has been shown theoretically that such superlinearity can result from a simple model of trapping states and recombination centers, provided that a disconnected competing trap or center is involved. Similar circumstances were shown to cause a dose-rate dependence of the measured TL. More recently, some results of OSL superlinearity have been reported. The present work provides a theoretical account of this e ect. A distinction is made between OSL due to relatively short pulses of stimulating light and the integral over a long illumination. It is shown that in the former, one can expect a quadratic dose dependence of the e ect provided one starts with empty trapping states and recombination centers. In the latter, superlinearity can be found only in the presence of competitors, in a similar way to the TL behavior. Also, the possibility of dose-rate dependence of OSL, which has not been reported in the literature is predicted and should be checked in future OSL measurements.
Thermoluminescence (TL) glow peaks were simulated over a wide range of absorbed doses using the interactive multipletrap system (IMTS) model. The absorbed dose range was divided into three regions; a region in which the measured TL signal grows quadratically with the absorbed dose, a supraquadratic dose-response region and dose-saturation region. The properties of the simulated glow peaks were investigated for each dose region. The different behaviors of the maximum peak position (T max ) with the absorbed doses were discussed. The applicability of applying the general-order kinetics (GOK), the mixed-order kinetics (MOK), and the developed one trap-one recombination (OTOR) center expressions on the IMTS glow peaks was investigated. The results showed that, in general, the developed OTOR expressions are the most apt expressions to be used in the peak-fitting method for the deconvolution of the experimental glow curves. The accuracy of the GOK and MOK expressions in describing the IMTS glow peaks is dependent on the value of the ratio of the trapping probability to the recombination probability (R ¼ A 1 /A m ) and the amount of the absorbed dose. New TL expressions based on the non-interactive multiple-trap system (NMTS) model were deduced.