AbstracCA composite thermoluminescent dosimeter (TLD), composed of four, thin TL elements with a high-speed reader, has been developed by employing an optical-heating method. Each TL element, which is 15mg/cm2 thick with a 3 m m dia., is prepared by applying Li2B407:Cu or CaS04:Tm to a plastic substrate 14 mg/cm2 thick. Each element can be heated to 350°C within 0.8sec. by IR radiation from a tungsten lamp. The characteristics of this TLD system include the following: (1) the detection limit of the Li2B407:Cu is 3 mR and the limit for CaS04:Tm is 0.1 mR; (2) the energy-dependence curves are similar to the doseequivalent curve, showing slight under-responses by 15% near 70 keV for Li2B407:Cu, and over-responses by 50% at high energies for CaS04:Tm; (3) despite quick heating, the residual dose is as low as 0.1% of the last exposure signal; (4) responses are very stable for more than 1 ,OOO cycles of repeated exposure readings; (5) no false signal could be detected, even in the cases of sweat or soil contamination; (6) the thin Li2B,07:Cu element can be used for skin dose monitoring; and (7) the processing time of the automatic reader for the composite dosimeter is 3 hr/SOO dosimeters. This TLD system can be applied to personnel dosimetry, gate monitoring and environmental monitoring.

Lithium or sodium doped beryllium oxide, BeO(Li: 0.5 mol%) and Be0 (Na: 0.5 molx), were found to be efficient and reliable thermoluminescent phosphors. Glow curves of both BeO(Li) and BeO(Na) have simple peaks at 18OoC. The thermoluminescent spectrum shows a broad band in the ultra-violet region peaking at 330 mp with shoulders near 300 and 390 mp.Besides featuring the characteristic that this material has a photoelectric absorption equivalent to that of biological tissue, the main characteristics of the phosphors, from the point of view of dosimetry include:(1) Exposure response of BeO(Li) is linear from 1 mR to 500 R, and that of BeO(Na) is linear from 2 mR to 100 R.(2) Fading of BeO(Li) is less than 20 % within the first hour and 8 % within the following 30 days, and that of BeO(Na) is less than 10 % within the first hour and 5 % within the following 30 days. Light fading of pray exposed BeO(Li) and BeO(Na) is less than 10% for a light exposure of 300 lux for 10 min.(3) After repeated use, easy annealing (heating at 450 -5OO0C for 1 -10 min) removes the residual dose.(4) The thermoluminescent efficiency remains unchanged after more than 100 cycles of repeated exposure-readout operations.(5) A small amount of tribo-thermoluminescence is emittable; about 15 mR dose equivalent for dropping 10 times from a height of 1 m to concrete floor.

Composite thermoluminescence dosimeters with elements attached to a small plate have been developed for use in mixed fields of y-rays, X-rays, /?-rays, and thermal neutrons.For photon dosimetry, CaS0,:Tm contained in a glass capsule or formed into a thin sheet with a resin is used. The glass capsule element covered with a tin shield is used to measure the photon dose over 70 keV and the sheet element covered with a carbon shield, that below 70 keV. A similar sheet element without a carbon shield is used for P-ray dosimetry. For thermal neutron dosimetry, a glass capsule element with a mixture of CaS0,:Tm powder and a 6Li compound is used. All of these elements are attached to an aluminum plate, 25 x 24 x 2.5 mm, on which small coded holes corresponding to individual personnel can be punched.The dose ranges of the elements are: 0.3mR-200R for photons over 70keV, 1 mR-200R for photons from 10keV to 70keV, 10mrem-2000rem for /?-rays, and 0.1 mrem-5 rem for thermal neutrons. Measurements of y-rays at 10 mR with a superposed dose of as much as 100 mrem from other kinds of radiation can be made with a standard deviation of less than 7%.

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