Ispitivanje aktivnosti radionuklida u otpadnom materijalu – budžet merne nesigurnosti

Abstract

Prema važećoj zakonskoj regulativi u Republici Srbiji kontrola radiološke ispravnosti otpadnih materijala vrši se na graničnim prelazima, kao i kada postoji namera odlaganja u životnu sredinu. Sadržaj radionuklida u otpadnim materijalima u najvećem broju slučajeva odredjuje se gamaspektrometrijskim ispitivanjem. Ova merenja podrazumevaju adekvatnu pripremu uzorka u cilju postizanja željene geometrije merenja za koju je izvršena kalibracija efikasnosti gama spektrometra. U postupku pripreme uzorka otpadnog materijala često nije moguće postići zadovoljavajuću homogenost. Takodje, matriks merenog materijala u većini slučajeva ne odgovara matriksu standarda pomoću kojeg je izvršena kalibracija spektrometra. Iz ovih razloga je potrebno izvršiti odredjene korekcije rezultata merenja (transfer efikasnosti, na pr.), kao i proširenje budžeta merne nesigurnosti. U radu je detaljno prikazan postupak procene doprinosa nehomogenosti uzorka mernoj nesigurnosti, kao i doprinosa koji u budžet merne nesigurnosti unosi transfer efikasnosti i primena korekcionih faktora za koincidentno sumiranje.

According to the current legislation in the Republic of Serbia, the radiological control of waste materials is performed at border crossings, as well as when there is an intention to dispose these materials in the environment. The gamma ray spectrometry is commonly used for determination of radionuclide content in waste materials. These measurements imply adequate sample preparation in order to achieve the desired measurement geometry for which the efficiency of the gamma spectrometer has been calibrated. Satisfactory homogeneity is often not possible to achieve in the sample preparation process. Also, the matrix of the measured material in most cases does not correspond to the matrix of the standard used for efficiency calibration of the spectrometer. For these reasons, it is necessary to make certain corrections to the measurement results (efficiency transfer, for example), as well as to expand the measurement uncertainty budget. The paper presents in detail the procedure for assessing the contribution of inhomogeneity of the sample to the measurement uncertainty, as well as the contribution that the efficiency transfer and coincidence summing corrections introduce to the measurement uncertainty budget.