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Burlin's general cavity theory for intermediate sized cavities incorporated two weighting factors: d, the average reduction in the electron fluence from the medium inside the cavity, and 1 - d, the average fractional build-up to equilibrium of the cavity-generated electron spectrum--both calculated for an average path length g of electrons crossing the cavity. A new weighting factor d' has been introduced expressing the fact that average path length for medium- and cavity-generated electrons are not equal and this leads to a modified general cavity expression. The new expression is applied to 60Co thermoluminescence dosimetry experimental results of other workers. For LiF TLD in all the media agreement with experiment is improved. There is a significant dependence of the theoretical results on the effective mass attenuation coefficient, indicating the need for further studies.

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A three dimensional model is developed to describe the linear-sublinear behaviour of the thermoluminescence JTL) dose response curve induced by heavy charged particles specifically 'low energy' (-1 MeV U-') alpha particles. Supralinearity induced by alpha particles is shown to be suppressed or non-existent owing to the very low probability \<2%) of overlapping tracks in the dose region 10-5000 Gy where electron induced supralinearity is normally observed. Description of the sublinear behaviour is based on calculations using the Monte Carlo as well as analytical methods in which the alpha particle track is described as a cylindrical volume whose height corresponds to the range of the alpha particle and whose effective radius, refir is a single free parameter, determined by fitting the theoretical dose response to experimental results. The calculations are based on the approximation that the sublinear behaviour is a result of overlapping tracks in which the overlapping regions are completely saturated, i.e., the increase in dose in the overlapping volume does not result in an increase in the TL signal. Using this assumption a theoretical dose response curve is obtained which is sublinear at high dose and in excellent agreement with experimental results as shown by X 2 / n values. The values for re* determined from other workers' data (for 5 MeV alpha particles stopping in LiF:Mg, Ti) for the glow peaks appearing at 130, 190, 255 and 390°C are 100 8, i X 2 / n = 1.3), 150 8, i ~* / n = 0.8), 85 8, i(X2/n = 1.07) and 70 8, (,y2/n = 2) respectively. The value of r e * = 150 8, for peak 5 is in excellent agreement with radial dose distribution data for alpha particles stopping in LiF. t The dose-TL response, f k ( D ) , of a uniformly irradiated mass of TL material is the ratio of the TL efficiency, Cik(D) at dose D to q(&) at 'low dose'&: thusfk(D) = a k ( D ) / C i k ( & ) . The thermoluminescent efficiency, Cxk, is the ratio of the mean energy emitted as TL light, Z+, to the mean energy, E, imparted to the TL material by the radiation field, cxk = Z+/E.

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