Justification and Application of Sufficiency Criterion for Measuring the Activity of Uranium Radioisotopes in Biological Samples

Purpose: Ensuring the fulfillment of the sufficiency n criterion when measuring the activity of uranium radionuclides in biological samples carried out within the individual monitoring programme by calculation of the uncertainty and characteristics limits for measurements. Material and methods: The sufficiency criterion definition is given, which determines the maximum value of the decision threshold for measurements carried out for the individual monitoring of workers at which the fact of non-exceeding of the annual dose limit or permissible level takes place, taking into account the uncertainty of the dose assessment. A model approach is used to calculate the sufficiency criterion and characteristics limits when measuring the radioactive material excrected by individual workers. The model approach consisted in the development of a calculation model based on the functional dependence of measured input values on the process of radiochemical preparation and subsequent spectrometric measurement of the sample. Results: A model has been developed for calculating the activity of uranium radionuclides 234U, 235U and 238U in a biological sample based on the description of the procedure for spectrometric measurement, which consisted in the deposition by the electrolytic method on the target after chromatographic extraction of uranium from the urine sample. The reference radioactive solution of the 232U radionuclide added to the sample as a reference point for determining the efficiency of uranium radionuclide separation (chemical yield). Equations are obtained for calculating the values of the decision threshold and the detection limit for the total activity of the above alpha-emitting uranium radionuclides. Using these equations, the dependence of the decision threshold and the detection limit on measurement time is determined for the given input data. This allows planning the measurement time at which the activity of uranium radionuclides in the sample can be determined reliably or at which the sufficiency criterion of the measurement method will be provided (necessary in the case when the activity is not detected, that is, the measurement result is less than the decision threshold). The values of the activity of uranium radionuclides 234U, 235U and 238U and the corresponding characteristics limits for the measurement were calculated on the basis of a real example of spectrometric measurement of the activity of uranium radionuclides in a sample. Conclusion: Ensuring the fulfillment of the sufficiency criterion when measuring the activity of uranium radionuclides in biological samples is achieved by the correct determination of the sample measurement time. This is determined by time dependence analysis of the characteristics limits (the decision threshold and the detection limit ) for the measurement of the total activity of the above alpha-emitting uranium radionuclides 234U, 235U and 238U.