Gamma Dosimetry at 250 exp 0 C by Thermoluminescence

摘要

A minor peak in the thermoluminescent glow curve of natural calcium fluoride has been found useful for dosimetry at elevated temperature. In particular it has been used for measuring the gamma dose rate profile along radioactive components under the molten sodium of the Prototype Fast Reactor at Dounreay. The glow peak occurs at about 410 exp 0 C for a heating rate of 10 exp 0 C per second. It corresponds to Peak IV in the numbering system of Schayes and lies 125 exp 0 C above the dominant peak, Peak III. For the same dose the height is about 1% of Peak III: nevertheless with a 5 mg sample a dose of 1 rad can easily be measured. The photon counting system employed a photomultiplier (EMI 9635QB) having a bialkali photocathode and ultraviolet and heat-rejecting filters. In the PFR measurements the dosimeters were exposed to the gamma fluxes at elevated temperature for 24 hours. Separate stability tests indicated that at 280 exp 0 C the loss was <10% in that period, and at a practical reactor temperature of 250 exp 0 C, much less. The low dose rates successfully recorded in this way are highly satisfactory for the operation and maintenance of the reactor at this stage in its life. (Atomindex citation 13:645718)