Influence of thermal quenching on the thermostimulated processes in alpha-Al2O3. Role of F and F+ centres.

Anion deficient alpha-Al2O3 is highly sensitive to ionising radiations and is widely used as a thermoluminescence and optically stimulated luminescence dosemeter in environmental monitoring. Two types of alpha alumina were studied and it was observed that both were affected by thermal quenching of luminescence. This effect, which manifests itself by the decay of the TL response when the heating rate increases, can be described by the Mott-Seitz theory. It was observed that thermostimulated exoemission response increased when the heating rate increased, whereas thermostimulated conductivity remained constant. However, none of the available theories could explain the dependence of the F- centre emission on the heating rate. A model is proposed to describe simultaneously the various thermally stimulated processes.

A new model for numerical analysis of simultaneously thermally stimulated luminescence and exoelectron emission phenomena of alpha-Al2O3 single crystals.

An efficient model to analyse numerically the simultaneously detected thermally stimulated luminescence (TL) and exoelectron emission (TSEE) dosimetric peak D' (450 K) of a-alumina is proposed. In this model, the TSEE obeys a thermionic mechanism. To take into account the fact that TL is a bulk phenomenon and that TSEE results from surface processes, a multilayer structure of the sample is adopted. In this work, two different approaches are discussed and compared. The first implies that the charge neutrality condition is applied to the sample alone, whereas in the second, the condition concerns the sample added to the detection equipment. The two models are applied to the dosimetric peak D' (at about 450 K) of alpha alumina and give very good results in both cases.

Characterisation of thermoluminescent LiF:Mg,Ti (MTS-N) detectors in the 85-550 K temperature range.

Miniature LiF:Mg,Ti (MTS-N) pellets, specially designed for dosimetry in proton radiotherapy, were studied in the 85-550 K temperature range. TL glow curves for differently Mg- or Ti-doped detectors were recorded, showing the preponderant influence of Mg concentration on the intensity of peak 5. The presence of a three-peak complex was also confirmed near 140 K; spectral emission of this peak consists of two bands whose maxima occur at 290 and 420 nm. TSEE glow curves above 300 K similar to those of TL were observed. The behaviour of TSEE and TL peak 5 following an X ray exposure from 33 to 500 Gy was studied: its intensity is a linear function of air kerma in both cases.