Comparison of field and laboratory methods to measure activity concentration of natural radionuclides in soil

Field gamma spectrometry is a common method for determining activity concentration of natural radionuclides in soil in situ. However, the method requires comparison with laboratory methods. Aim of the study: Comparison of field and laboratory methods for measuring activity concentration of[226] Ra,[232] Th and 40K in soil in the presence of surface radioactive contamination with 137Cs. Materials and Methods: Field measurements and soil sampling were carried out simultaneously at 10 kitchen garden plots located in six settlements of radioactively contaminated ([137] Cs) zone of the Bryansk region of Russia. In situ measurements were performed using the MKS-AT6101D scintillation gamma spectrometer-dosimeter from ATOMTEX (Belarus). For the laboratory measurements, a semiconductor gamma spectrometer from ORTEC (USA) was used. Results and Discussion: No statistically significant differences were found between the two methods for determining activity concentration of the natural radionuclides in soil (Wilcoxon test, P > 0.05). The Spearman’s correlation coefficient was 0.87, 0.77, and 0.89 for[232] Th,[226] Ra, and[40] K, respectively. The maximum discrepancy between the laboratory and in situ results was 32 %; on average, the difference ranged from 2 to 8 %. The largest differences were found for[226] Ra. This is mainly due to the measurement uncertainty, which was highest for this radionuclide, compared to[232] Th and[40] K, in both field and laboratory measurements. Conclusion: The comparison study showed that the results obtained using field gamma spectrometry under conditions of contamination of the territory with the technogenic radionuclide[137] Cs were in good agreement with the results of laboratory measurements. There is no need to adjust the activity concentration values obtained using calibration, which was performed by the manufacturer of the portable gamma spectrometerdosimeter MKS-AT6101D.

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