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

摘要

A cryostat based integrated TL/OSL reader has been designed and developed to study the temperature dependence of photoionization cross-section at various low temperatures. The system has the facility to record thermoluminescence (TL) as well as optically stimulated luminescence (OSL) at various low temperatures from -150 to 250 degrees C. It facilitates the measurement of OSL at various temperatures thus; temperature dependence of OSL at various low temperatures can be studied. A PID (Proportional-Integral-Derivative) based temperature controller has been designed and incorporated for generating and controlling user defined heating profiles for the TL measurements in the reader system. The reader system can measure the temperature of the planchet within +/- 1 degrees C precision. The optical stimulation unit consists of two high power LEDs fitted in two channels and optically focused on the sample. In the OSL operation, besides the conventional CW-OSL, LM-OSL modes a nonlinear OSL (NL-OSL) method has been incorporated in the reader system. The sensitivity of the system is found to be comparable to that of commercial Riso reader system in OSL mode. The OSL grade alpha-Al2O3:C phosphor was used to test the reader system and investigate the temperature dependence of OSL in this phosphor at low temperature regime. We report the results of OSL experiments on alpha-Al2O3:C, and of generalized numerical simulations of potential OSL behaviour with temperature. The photoionization cross-section of shallow as well as dosimetric traps has been evaluated numerically as well as experimentally. The design concept of the reader system and the results of low temperature OSL are discussed.