Berestov R. The method of extending the service life of closed sources of ionizing radiation

The dissertation is devoted to the study and solution of the problem of extending the service life of sealed ionizing radiation sources used in Ukrainian industry. The analysis of metrological support of sealed sources of α-, β-, and γ-radiation was carried out. The analysis of different types of ionizing radiation sources and their technical characteristics is carried out. The reference base of ionizing radiation sources and methods for measuring the activity of nuclides are considered. The legislative and regulatory support of sealed radiation sources is considered. The aim and objectives of the study are formed. The requirements for the method of extending the service life of sealed sources based on calibration results are formulated. A mathematical model in the form of a system of inequalities for the method of extending the service life of sealed radiation sources based on the analysis of changes in their metrological characteristics during their service life was developed. The existing method of calibration of sealed sources was analyzed and the need for its improvement was determined by adding the process of checking ionizing radiation sources for leaks. A methodology for checking a sealed ionizing radiation source for leakage is developed and the components of its uncertainty are analyzed. The necessity of leakage testing of sealed sources before their calibration is substantiated. The equation of the extended uncertainty of the results of calibration of sealed sources with regard to the leakage test was formed, which made it possible to increase the accuracy of the uncertainty assessment. A methodology for the use of control cards to control the statistical controllability of the process of changes in the metrological characteristics of a closed source has been developed. In order to predict the process of changes in the metrological characteristics of a closed source, a comparative analysis of the application of extrapolation methods was carried out and the use of regression analysis and the least squares method was proposed. The calibration results for the life cycle of a sealed radiation source were described by different regression functions. The choice of the function for prediction, which most accurately described the results obtained, was substantiated. Taking into account all the results obtained, a method for extending the service life of sealed radiation sources was developed. The choice of the period for which the service life of a sealed source is extended is substantiated. Experimental studies and mathematical modeling of the method for extending the service life of sealed sources were carried out. The uncertainty of calibration results was estimated. The modeling of the choice of function for describing changes in the activity of a sealed source based on the results of calibration and for predicting the service life of a sealed radiation source was carried out.