Remeasurement of early Harwell personnel film dosimeters

The A.E.A. epidemiological study depends for its radiation dose data on records of film badge doses which have been stored continuously since 1947. The records were originally kept to assist in the control of radiation hazard to the individual and for that purpose doses below the measurement threshold were unimportant. The epidemiological study could consider these doses to be either zero or equal to the measurement threshold, but both assumptions risk introducing a bias. Samples of old films worn in 1955 and 1960 were therefore remeasured using the present-day lower threshold of 0.005 rems to aid the choice of the most correct estimate. It was found that there had been little change in the blackening on the films or in the assessed radiation dose for 238 films above the original threshold of 0.05 rems, confirming that remeasurement was possible. The 2426 films previously recorded as ''<0.05 rems'' were found on remeasurement to give an average dose of 0.009 rems. A similar epidemiological study of radiation workers at Hanford took threshold doses as equal to zero and considered only positive measured doses. The errors possible with this approach are discussed. (author)