Development of cryostat integrated TL/OSL reader for its application in radiation dosimetry

Thermoluminescence (TL) studies provide vital clues in connection with the mechanism of trap formation, concentration and nature of the traps. For a radiation phosphor generally, dose readout is carried out at the temperatures that are much higher than normal room temperature where shallow traps are ineffective and as such cannot contribute to the TL response. In OSL based dosimetry, however, the measurement is usually carried out at room temperature, where these shallow traps can significantly affect the OSL response. The TL measurement at low temperatures gives the useful information about such shallow traps which may be having metastable life-time of the order of a few ms at room temperature. It has been observed that these traps exercise a decisive influence over the OSL response of samples as they lead to a delayed optically stimulated luminescence (DOSL) in which charges released from dosimetric traps, upon optical stimulation get re-trapped at shallow traps. At lower temperatures (below room temperature), these traps may contribute to the total OSL signal and at the same time the contribution of higher temp TL traps will decrease due to the temperature dependence of photoionization cross-section. Thus, they can seriously affect the overall calibration factor for any dosimeter with the change in the readout temperature. This can have implication in optical fibre based online OSL dosimetry which can find application in medical dosimetry. This lead us to develop the low temperature TL/OSL reader to study the TL/OSL of Al₂O₃:C OSL phosphor to be used in optical fibre based OSL dosimetry