Study of real time temperature profiles in routine TLD read out--influences of detector thickness and heating rate on glow curve shape.

This paper reports the results of a study using a commercial routine read out system with non-contact hot nitrogen heating and linear heating gas profiles. Glow curves of LiF:Mg,Ti as well as LiF:Mg,Cu,P were analysed for different linear heating rates beta from 1 to 30 degrees K s(-1). Different thermoluminescent detectors (TLDs) of different thicknesses (0.38-0.90 mm) were studied and compared. By means of the application of CGCD program considering kinetic parameters of the used TL-material the analysis of the peak temperature of the individual TL peaks lead to the approximation of the real heating profile T(chip)(t) in the TL chip. The real heating profile deviates strongly from linearity and can be characterised by the solution of a differential equation T(chip)(t) = F [T(gas)(t)]. The model of this equation is discussed in the paper. The difference between gas and chip temperatures are heating rate and chip thickness dependent and reach values of up to 100 degrees C (for thick detectors and fast heating rates). Especially for LiF:Cu,P, knowledge of the real chip temperature is essential, since read out shall be performed at the highest possible temperature, without destroying the dosimetric properties of the material. On the basis of this work, an optimisation of the readout parameters for LiF:Cu,P is possible.