A Practical Procedure to Determine Natural Radionuclides in Solid Materials from Mining

Abstract

There are many regulations related to the radiological control of NORMs (Naturally Occurring Radioactive Materials) in activities such as mining, industry, etc. Consequently, it is necessary to apply fast and accurate methods to measure the activity concentrations of long-lived natural radionuclides (e.g., U-238, Th-234,Th-232,Th-230,Th-228, Ra-228,Ra-226, Pb-210, Po-210, and K-40) in samples characterized by a wide variety of compositions and densities, such as mining samples (wastes, minerals, and scales). Thus, it is relevant to calculate the radioactive index (RI), which summarizes for all radionuclides the ratio between the activity concentration and its respective threshold activity concentration as established by regulations, in order to classify a material as a NORM. To proceed with the determinations of these radionuclides, two spectrometric techniques based on both alpha-particle and gamma-ray detections should be employed. In the case of gamma-ray spectrometry, it is necessary to correct the full-energy peak efficiency (FEPE) obtained for the calibration sample, s o due to self-attenuation and true coincidence summing (TCS) effects. The correction is especially significant at low gamma emission energies, that is, E-gamma < 150 keV, such as 46 keV (Pb-210) and 63 keV (Th-234). On the other hand, in samples which contain radionuclides that are in secular disequilibrium with others belonging to the same series (U-238 or Th-232 series), like wastes or intermediate products, it is necessary to measure some pure alphaemitters (Th-232, Th-230, Po-210) by employing alpha-particle spectrometry. A practical and general validated procedure based on both alpha and gamma spectrometric techniques and using semiconductor detectors is presented in this study.