Gamma dose measurement with film badges in the presence of large fluences of thermal neutrons

Personnel monitoring films in chest holders are used for evaluating X and gamma doses received by the users. This way of measuring gamma doses may not be very accurate if the wearer encounters large thermal neutron fluences because the silver content of the photographic emulsion undergoes activation giving rise to increased optical density which results in the overestimation of gamma dose. This paper gives the results of a study conducted to obtain optical densities due to thermal neutron activation. Kodak Type II films, not studied before, were exposed to a thermal neutron flux of 6.8x108 n/cm2s for various periods and it was found that under the copper filter (1 mm thick) a density equivalent of 4.2 R of 60Co gamma radiation for a fluence of 1010n/cm2. This Division participated in the International Intercomparison Experiments on Nuclear Accident Dosimetry Systems organised by the IAEA and the above result was made use of in arriving at the gamma doses. It was found that the gamma doses measured with the film, after applying the activation corrections, agreed well with the results obtained with CaSO4:(Dy) thermoluminescent dosimeter. (Auth.)