Technical Feasibility of the Dose-to-Curie Conversion Method for a Radwaste Drum Assay

The dose-to-curie (DTC) conversion method is a very simple and easy way to estimate the radioisotope inventory of a drum by a non-destructive assay method. So, in order to make the dose-to-curie conversion method practical, the parameters affecting the measured dose rate were evaluated by using the MCNP code. The major uncertainties associated with measuring the dose rate from a drum could be divided into the impact of the elemental composition of the contained material, and of the spatial distribution of the radioactive sources in a drum. Also, the relative abundance of gamma emitters in a drum, another source of uncertainty at the DTC conversion, could be directly obtained from the measured pulse height spectrum. The dose rate of that drum could then be calculated by using a dose conversion factor which is widely used in the field of environmental radiation measurement. As a result, the impact of the elemental composition and the spatial distribution of radioisotopes within a 200-L drum with a low density could be reduced if the detection points are selected at three times the radius of a drum.