Sublinear dose dependence of thermoluminescence and optically stimulated luminescence prior to the approach to saturation level (original) (raw)
Related papers
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.
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.
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.
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.
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 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.
Characterization of nonlinearities in the dose dependence of thermoluminescence
Radiation Measurements, 1994
Nonlinearities often occur in the dose dependence of thermoluminescence (TL). These include sublinearity, usually when there is an approach to saturation in the dose dependence, as well as supralinearity, also termed superlinearity in the literature. Different researchers in the field have viewed the effect of supralinearity/superlinearity from two somewhat different points of view. One point of view has to do with the rate of change with dose of the dose dependence function. The other approach is related more to the applications of TL in dosimetry and archaeological and geological dating, and basically has to do with the correction to be made in extrapolation in cases where supra(super)linearity occurs following an initial linear dose range, or prior to such a linear range. In the present work we propose quantitative methods to characterize these nonlinearities. We suggest the use of two different nonlinearity indices, depending upon how one wishes to describe the nonlinearity. We propose use of the term "supralinearity index", f (D ), in cases where the feature of interest is the deviation from linearity, namely, when the correction in extrapolation is the main issue. We propose the term "superlinearity index", g (D ), in dose ranges where the growth is "more than linear" and when extrapolation is not the main issue. We mathematically define each of these indices and give examples of their use for different dose dependencies.
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.