A comparison of alpha and gamma spectrometry for environmental natural radioactivity surveys

An α-spectrometry, using automated borate fusion and sequential extraction and exchange chromatography, was used to determine the uranium and thorium based on environmental radioactivity of 20 soil samples. The same set of the samples was analysed using γ-spectrometry with an HPGe detector. The two data sets were checked for coherence using Z-score and χ2 statistical tests. We show that γ-spectrometry is a valid alternative to time-consuming α-spectrometry for the determination of natural uranium and thorium activity in soil (activity range: 12.5–58.2 Bq/kg). The measured activities were compared with the theoretical activities to ensure secular equilibrium in the 238U and 232Th series. For 226Ra, a special study was made on deconvolution of the 186 keV multiplet with the Levenberg–Marquardt algorithm. Finally, the combined use of Z-score and χ2-tests was found to be a powerful tool for comparing the results obtained with two different methods.