Supralinearity and LET dependence of thermoluminescence dosemeters

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Abstract
The authors recent investigations indicate that the major factor responsible for supralinearity of TL response to low-LET radiation is possibly the transfer of energy to the dosimetry traps or luminescent centres during irradiation (and readout) as a result of sublinear rise (caused by radiation damage) of the competitors with increasing dose. The nature of the traps (1- or 2-hit) has no perceptible bearing on the dose-response relations for low LET radiations. Experiments have shown that a 1-hit trap (Z3 centre in LiF TLD-100 giving rise to peak 10) is more supralinear than a 2-hit trap (Z2 centre in LiF TLD-100 giving rise to peak 7). These observations indicate that Katz's supralinearity model of dose against TL response at low LET is inappropriate. Similar to biological systems, the nature of the trap has some perceptible bearing on its TL-LET response. However, a 2-hit trap (Z2 centre in LiF TLD-100) has been found to have higher TL (RBE=2) efficiency for X-rays (30-100 keVeff) rather than for high LET radiation. This was explained on the basis of increased probability of filling of traps with 2 electrons in the X-ray (30-150 keV) region and energy wastage in the high-LET range compared with 60Co gamma radiation. It is likely that a 3-hit trap in LiF might mimic biological systems and thereby exhibit the desired LET response (RBE approximately=10 for high-LET radiation) for fast neutron dosimetry.

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