Thermoluminescence, optically stimulated luminescence and radiophotoluminescence dosimetry: An overall perspective

Radiation dosimetric methods are used for the estimation of dose absorbed by radiation in a detector material. These methods are required for estimation of absorbed dose in various applications of radiation, such as personnel and environmental dosimetry, retrospective/ accident dosimetry and medical applications of radiation. The use of thermoluminescence (TL) as a method for radiation dosimetry of ionizing radiation has been established for many decades and has found many useful applications in various fields, such as personnel and environmental monitoring, medical dosimetry, archaeological and geological dating, space dosimetry. Several high sensitivity TL phosphor materials and thermoluminescent dosimeters (TLDs) are now commercially available in different physical forms. There are many commercial TLD systems which are being used for various dosimetric applications and even presently, TL is a major player in the field of radiation dosimetry, particularly in personnel dosimetry. In the last two decades an alternative technique, optically stimulated luminescence (OSL), has been developed, as the optical nature of the readout process does not involve problems of blackbody radiation and thermal quenching. Due to this and some other advantages OSL is also being used for various applications in radiation dosimetry, such as personnel and environmental dosimetry, retrospective/ accident dosimetry and medical dosimetry. The development of Al 2 O 3 :C TL/OSL phosphor by Akselrod et al. and later investigation of its suitability for personnel dosimetry using pulsed OSL (POSL) technique of stimulation by Akselrod and McKeever, resulted in the development of a personnel dosimetry system based on Al 2 O 3 :C OSL phosphor. Therefore, thrust of modern luminescence dosimetry development is more towards OSL. The main advantages of the small size optic fiber based OSL dosimeter over the currently available radiation detectors, such as TLD, used in clinical applications, are the capabilities of measuring both real-time dose rate (using radioluminescence, RL) and absorbed dose (using OSL). Although radiophotoluminscence (RPL) dosimeters were developed in parallel with TLD systems during 1960s, but high pre-dose and photon energy dependent detector material prevented major breakthrough of the glass dosimetry. Therefore, RPL glass dosimeters were used as an emergency dosimeter in accident situations. However, in mid 1980s introduction readout systems using a pulsed UV stimulation, in place of conventional mercury UV lamps, helped in reducing pre-dose by a factor of 100 (from mSv to a few μSv). Use of pulsed stimulation permits electronic discrimination of the signals from the pre-dose and absorbed dose on account of their different fluorescence decay times. This development resulted in the manufacture of improved RPL glass dosimeters and fully automatic RPL reader systems capable of measuring doses in the range 10μSv to 10Sv. In 2001, silver activated phosphate RPL glass dosimetry system has been introduced as the major personnel monitoring service in Japan marketed by Chiyoda Technol Corporation. Some of these developments in the field of TL, OSL and RPL dosimetry are reviewed.