Cooled optical luminescence dosimetry in plastic matrices

Large-scale dosimetry services such as Landauer, Inc., require cost-effective, easy-to-manufacture dosemeters that are available in high volume with good precision and uniformity between batches. The ability to re-analyse a dosemeter and to perform necessary exposure diagnostics familiar to film dosimetrists are also desirable qualities of a dosimetric system. Battelle has developed a cooled optical luminescence dosimetry (COLD) system that allows all these features to be combined into one practical dosimetry system. COLD technology uses an extremely sensitive phototransfer mechanism manifested in certain solid state materials. Modest cooling below room temperature is required during the readout of the COLD detectors. Excitation with a laser or other light source is required to initiate the phototransfer process. Warming to near room temperature liberates the luminescence that is proportional to the radiation exposure. Due to the low readout temperatures, COLD phosphor materials can be packaged in polymers without fear of melting the polymer matrix, as would occur using a thermoluminescent process. Besides extreme sensitivity (minimum detectable exposure levels of 0.1 mu Sv are possible), the detectors can be re-analysed with minimal loss of signal. An imaging film is created by the mixture of small grains of COLD phosphor in the polymer matrix. A sensitive CCD or microchannel PMT device acquires a two-dimensional image of the dosemeter luminescence. The resulting digital image can then be mathematically interrogated to determine exposure diagnostics in the same way that film is currently used.