The evaluation of electret ionization chambers as a field screening method for samples containing natural and depleted Uranium

Electret ionization chambers have been experimentally evaluated as a field screening method for samples containing natural and depleted uranium. Correlation factors relating the electret's response to uranium standards were experimentally determined and tested. The method was tested on unknown samples in an environment similar to what is expected in radiological characterization studies. Results of the tests indicated this method gives satisfactory results provided sample preparation and ambient environmental conditions are satisfied. The loss of radon from the samples during sample collection and processing was investigated with regard to the decay and regrowth of radioactivity during the period of sample analysis by means of a computer code "EQUIL" developed during this work and by experimental methods. The experimental methods included 1) heating a uranium pitchblende standard and evaluating the changes in the radioactive daughters of radon and 2) agitating a pitchblende standard to simulate the mechanical processing and evaluating the changes in the radioactive daughters of radon. Both the heating and agitation were performed at extremes of normal procedures and for the standards tested no more than 10 percent of the radon was lost from the standards. Standards of 10, 30, 50, and 100 pCi g^{-1 238}U were measured on multiple occasions for both natural and depleted uranium. The correlation factor for natural uranium was calculated to be 1.99 V d^-1/ pCi g^-1. The correlation factor for depleted uranium was calculated to be 0.18 V d^-1/ pCi g^-1. These correlation factors are specific to the type of electret, the sample size (20 g), the sample container and the nuclides studied.