The theoretical and microdosimetric basis of thermoluminescence and applications to dosimetry

Abstract

TLproperties of many materials and their interaction with various types of radiation fields.+ The thermoluminescent efficiency, ak, is the ratio of the mean energy emitted as TL light, E+, to the mean energy, E, imparted to the TL material by the radiation field, a k = E+/B. d is sometimes referred to as the 'integral' dose in the irradiated volume and is defined as the expectation value of the imparted energy. $ The relative TL response, q k , , of a TL material of mass m, and volume V, is the ratio of the TL efficiences for the two radiation fields, k, I at 'low dose' Do, i.e. where .E+ is increasing linearly with dose:ak(Do)/ar(Do). 9: A tissue-equivalent material is one with atomic composition which closely approximates to the atomic composition of tissue. TL materials such as LiF, Li2B407, Be0 are nonetheless referred to as approximately 'tissue-equivalent' materials in gamma radiation fields because their effective atomic number and mass energy absorption coefficients for photoelectric absorption approximate to those of tissue (e.g. Jayachandran 1971).Y S Horo w itz irradiated material. Johnson also describes the use of an integrating period in the readout cycle which approximately cancels the growth of peaks 4-5 due to storage by including a certain fraction of peaks 2-3 which exhibit stronger fading. Ehrlich (1974) using fast preheating to 160°C did not observe 'sensitivity-transfer' in TLD-700; however, fading increased to 15% after 4 days. Indeed the fading of 'unannealed' LiF-TLDS is strongly dependent on the preheat cycle (Webb and Phykitt 1971, De Planque et a1 1980). Mason et a1 (1976) studied the effect of Ti in TLD-700 ( T1 = 300 "C, tl = 30 min) on the relative trap distributions associated with peaks 2 and 5 and concluded that the results of Booth etal (1972) were inconsistent with their data.'7. '7.' 7.

Alpha particle and proton relative thermoluminescence efficiencies in LiF:Mg,Cu,P:is track structure theory up to the task?

“…The systematics of the decreasing relative HCP TL efficiency with LET was described more than three decades ago (14) along with microdosimetric calculations based on modified TST (15) . In these early studies, D(r) for low-energy alpha particles stopping in LiF was calculated using scaling techniques, which were used to extrapolate from Monte Carlo calculations in gas and f (D) was measured experimentally in both nitrogen and air-annealed samples with 60 Co gamma rays, 50 kV p and 20 kV p X rays as well as 3 H beta rays.…”

“…f(D) max 3-5 for 60 Co gamma rays decreasing to 1.8 for 20 kV p X rays ( Figure 7). This dependence of f(D) on photon energy is attributed to the competition between localised and de-localised recombination in the UNIM (4,29) and motivated the development of modified TST (MTST) (14,15) in which it is required that f (D) be measured with photon or electron energies that create a secondary electron energy spectrum approximately matched to the HCP-generated electron spectrum.…”

“…R max and r max are the maximum axial and radial distances of penetration of the charge carriers from the HCP path (in the radiation absorption stage); f d (D) is the TL dose-response measured with a test electron radiation chosen to mimic the radiation action of the HCP as closely as possible. Further information is available in other publications (4,14,15,33) . Due to the great variability of even relative quantities in TL characteristics, it is necessary to emphasise the importance of measuring f d (D) under experimental conditions and protocol identical to the experimental measurement of h HCP,g (34,35) .…”

“…However, the only relative efficiency of 0.065 obtained by deconvolution (46) for GR-200 is actually the highest of the relative efficiencies-contrary to expectations. The rather low value of 0.02 (47) may be due to the use of grains of powder which are more susceptible to surface effects and possible 'dead' layers (14) . In an additional study (9) , the values of h a,g for 5-MeV alpha particles as a function of Mg concentration were shown to be constant at a value of 0.06 from 0.2 to 0.8 M % and then increase to 0.13 at 0.05 M % correlated with the appearance of supralinearity in the dose -response of this material Measured by computerised glow curve deconvolution.…”

A review of TLD's zero-count based on temperature and radiation history of them

“…Second, the spectrum of the thermoluminescence is highly dependent on the composition of the material and is only slightly affected by the temperature of heating [5]. In the usual thermoluminescence experiments, the system is treated at a temperature at which the phosphorescence intensity is low, and later heated through a temperature range where the phosphorrescence intensity is bright, until a temperature level at which all the charges have been thermally excited out of their metastable levels and the luminescence completely disappear [6,7]. The thermoluminescence emission mainly is used in solid state dosimetry for measurement of ionizing radiation dose.…”