On-line gamma flux measurements by means of a self powered gamma detector

Gamma flux profiles by means of a Self Powered Gamma Detector (SPGD) have been measured in a gamma irradiation facility using ⁶⁰Co sources, situated in the side pool of the BR2 materials testing reactor. Because of its small size (diameter of only 4 mm), the SPGD is ideally suited to perform very localised gamma flux measurements. It has been shown that the SPGD can provide accurate (order 0.3%) relative measurements of the local gamma flux in the range 0.5 to 30 kGy/h. An attempt was made to perform an assessment of the absolute precision of the SPGD measurements by comparing the SPGD measurements to the fluxes as derived from Red Perspex dosimeters but this turned out to be impossible due to the large uncertainty (20 to 50%) associated with the Perspex dosimeters. A very detailed Monte Carlo code has been developed to relate the gamma flux (for a given gamma spectrum) to the current induced by the SPGD. The obtained conversion factor could thus be used to determine the absolute gamma flux.