Estimation of below measurement threshold doses following the remeasurement of a sample of old films

An epidemiological study relating the mortality experience of United Kingdom Atomic Energy Authority employees to their radiation dose is currently in progress. For some early years dosimetry films were issued weekly and then assessed quantitatively only if the dose were above the current measurement threshold. This procedure, although satisfactory for protection purposes, is inadequate for epidemiological analysis because a substantial fraction of the collective dose is not quantified. A large random sample of 1953-61 films from Harwell has been remeasured using a threshold equivalent to 50 μS v (5 mrem) and the resulting data analysed using a weighted multiple regression procedure. The remeasured dose on these films below the original threshold can be expressed in terms of (i) the proportion of a wearer's films for the year which were recorded as ''below-threshold'' and (ii) the proportion of all firms worn at Harwell in that year which contained a positive dose at the original measurement. These relationships enable estimates of below-threshold doses to be obtained for other workers in other years. (author)