Non-monotonic dose dependence of thermoluminescence (original) (raw)
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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.
Dose dependence of thermoluminescence peaks
Journal of Physics D: Applied Physics, 1974
The dependence on the excitation dose of the maximum thermoluminescence intensity as well as of the peak temperature are investigated theoretically. It is shown that certain irregularities of the dose dependences can be explained by assuming the existence of a trapping level, the transition into which competes with the retrapping and recombination of the free carriers. By numerical solution of the appropriate equations, it is demonstrated that the maximum thermoluminescence intensity may depend superlinearly on the excitation dose. The power of the dose dependence was found to be 2 under certain circumstances at low doses, and reached even higher values before saturation of the competing level. The maximum temperature sometimes behaved in an unusual way; namely, it increased with increasing dose. The relation between the area under a glow peak and its maximum intensity is also studied; it is shown that the latter can usually serve as a measure for the former. This finding is of practical importance, especially in thermoluminescent dosimetry, since the evaluation of the maximum intensity is obviously more convenient than that of the area.
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.
Modeling the Pre-Dose Effect in Thermoluminescence
Radiation Protection Dosimetry, 1999
The increase of sensitivity of quartz by  or ␥ irradiation, followed by high temperature activation has been studied. The model previously suggested, including a reservoir through which holes get into the recombination centre, thus increasing the sensitivity to a given test dose, is now given a concrete mathematical form. Sets of simultaneous differential equations for the different stages of irradiation and heating are numerically solved sequentially so as to simulate the physical processes taking place. The dependence of the sensitivity on the excitation dose is followed, in particular at the high doses where the sensitivity approaches saturation. The assumption of exponential approach to saturation is tested, showing that, indeed, even in this complicated situation the exponential approximation is valid.
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.
On the theoretical basis for the duplicitous thermoluminescence peak
Journal of Physics D: Applied Physics, 2009
The simultaneous release of electrons and holes by what seems to be a single trap has been observed experimentally. We previously performed numerical simulations on a phenomenological model which showed similar behaviour. Here, we provide an analytical solution to this model. This model explains trends in radioluminescence, thermoluminescence and thermally stimulated conductivity of a material with one electron trap, one hole trap and one radiative recombination centre, in which thermal excitation of the electron trap occurs before that of the hole trap. It is shown that TL emission due to electron recombination at centres can be controlled by a hole trap and the electron recombination will have a peak shape associated with the hole trap's parameters. When this happens, the peaks in free electron concentration, free hole concentration and TL all occur nearly simultaneously. The analytical model allows this to be explained along with scaling laws and initial rise behaviour. Under the conditions illustrated by this model, the usual methods used to distinguish between electron traps and hole traps will give incorrect results.
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.
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.