Third Personnel Dosimetry Intercomparison Study PDF Download

The Health Physics Research Reactor (HPRR), used unshielded, with a 12-cm-thick Lucite shield or a 13-cm-thick steel shield, provided three neutron and gamma-ray spectra for personnel dosimetry intercomparison studies. The characterisitcs of these fields, such as neutron energy spectrum, intensity, and uniformity, had been measured previously during nuclear accident dosimetry studies. Exposures were made to simulate total exposures likely to be encountered in personnel dosimetry. Neutron dose equivalents of the order of 500 mrem were produced. Dosimeters were mounted on the trunk section of water-filled phantoms, the front edges of which were located three meters from the reactor center. When shields were used they were placed at two meters. Sulfur pellets exposed at a standard location on the reactor during the intercomparison were used to calculate values of tissue kerma for neutrons at the three meter position based on previous measurements. Hurst proportional counter measurements made at the time of the exposures are in good agreement with these results. The gamma component of dose, typically of the order of a few tens of mrad, was measured with LiF thermoluminescent dosimeters (TLD's). Using the fission yield and the calculated leakage of the HPRR, the neutron fluence was calculated for each reactor run. Then the dose was calculated based on the HPRR neutron spectra and the dose conversion factors which had been calculated previously for the three spectra. The results of these personnel dosimetry intercomparison studies reveal that estimates of dose equivalent vary over a wide range. The standard deviation of the mean of participants data was typically in the range of +-30 to +-40%. It is anticipated that this type of dosimetry intercomparison study will be worthwhile on an annual basis until the problems in dosimeter response and interpretation have been identified and solved.