Porcelain slices have been used as a dosemeter to measure low gamma doses at 300 oC in the Prototype Fast Reactor at Dounreay. At the 1980 Toulouse Conference Aitken, Bussel and Voice reported the use of the 430 oC peak of natural fluorite to measure the gamma flux at 250 oC and comparisons were first made against this technique. By using porcelain slices cut into sections 7 mm square and 200 µm thick and encapsulated in aluminium, it is possible to measure the gamma flux up to a temperature of 500 oC. The sensitivity changes induced in the 100 oC peak (the so-called pre-dose effect) enable minimum dose evaluations to 10 mGy ± 10% to be made. This sensitivity change is activated by post-irradiation heating to 600 oC; at 300 oC only 4% of this change has been activated, but at 500 oC, 25% change is observed. This limits the temperatures at which exposure can be made although higher temperatures are possible if lower accuracy is acceptable. There is no detectable loss due to thermal fading. Allowance is made for irradiation at elevated temperature by laboratory tests using a 60Co source. An added advantage with this technique is that after suitable thermal treatment, the slices can be re-used.
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