Determination of soil depth profiles for ¹³⁷Cs and ²¹⁰Pb using gamma-ray spectrometry with Compton suppression

Summary

¹³⁷Cs and to a lesser extent, ²¹⁰Pb have been widely used for soil erosion and sedimentation studies. The accuracy of their quantification is greatly dependent on the proper handling of the sources of error that may affect the results. These include ambient background variation, attenuation for the ²¹⁰Pb 45 keV gamma-photons in the sample, efficiency calibration and large statistical errors due to low levels of radioactivities and small sample quantities combined with Compton scattering of high energy photons during acquisition. In this study, we investigated the distribution of both ²¹⁰Pb and ¹³⁷Cs in three soil cores from Konza and Fort Riley, Kansas. Special attention was given to the analytical treatment of the spectra and the uncertainty budget. We show here that the ambient background is a major factor in the results. If it is not well monitored, errors of as high as 25% can result. We investigated the advantages of using Compton suppression with gamma-ray spectrometry for ¹³⁷Cs and ²¹⁰Pb quantification. Natural matrix certified reference materials (CRM) were used for efficiency calibration and quality assurance.