Nuclear accident dosimetry systems. UK measurements at the fourth I.A.E.A. intercomparison at Harwell, April 1975

An international Intercomparison of Nuclear Accident Dosimetry Systems was held at Harwell in April 1975 under the auspices of the IAEA. The source of radiation was the pulsed reactor VIPER at AWRE Aldermaston. This paper presents the results of the measurements made by the Harwell team which participated in the Intercomparison. For the neutron dose measurements standard nuclear accident dosimeters were exposed on a Bomab phantom and in free air. In the UK system of nuclear accident dosimetry the fast neutron dose is measured by sulphur activation together with, if possible, another detector with a lower threshold, namely either indium (sup(115m)In activation), body sodium (24Na activation) or neptunium. Fast neutron dose estimates were made by sulphur alone and by the other three methods. The results were consistent with those expected on the basis of previous work, except for the method involving body sodium. The results have been compared with those calculated from measurements before the Intercomparison with an ionization chamber system and neutron spectrometers. Some gamma-ray dose measurements were made with the TLD's in the standard criticality lockets, but, because of the large correction expected for (n,γ) dose from the foils in the lockets, the principal gamma-ray measurements were made with experimental TLD's and with special film dosimeters containing no cadmium. These agreed satisfactorily with each other and with the ionization chamber measurements. (author)