Uncertainty assessment of measurement of Cs-137 in water using gamma spectrometry method

A useful benchmark for the reliability of gamma spectrometry results is to provide measurement uncertainty. Due to the importance and necessity of radiation monitoring in water resources, this research has been oriented toward providing measurements of the gamma- emitting radionuclides along with introducing the expression for the uncertainty that appeared in these measurements. To calculate the uncertainty of the activity measurements in water, a sample, where its radioactive elements were obtained from the PolAtom Company, was used. The calculations were performed based on the 661 keV peak of 137</sup>Cs radionuclide and a high-purity germanium detector (HPGe). The investigations show that the factors affecting the measurement uncertainty are composed of two parts, including counting with the gamma spectroscopy system and sample preparation, where each of these parts comes from several sources of uncertainty such as uncertainties associated with the counting process, efficiency calibration, emission probability, the counting correction factors, and the mass measurement. The results of analyses show that the relative uncertainty is about 3.7% (Coverage factor = 1) for a water sample with an activity of 425 Becquerel from 137</sup>Cs.