Destructive and non-destructive measurements of NORM in monazite-rich sands of Brazil

The Earth and its atmosphere contains a range of Naturally Occurring Radioactive Materials (NORMs), with all minerals and raw materials containing trace amounts of radionuclides of natural origin. For most human activities, the levels of exposure to the decay of these nuclides constitute the natural radiation background level. There are areas known for their particularly high levels of background radiation compared to the World average, including some specific Brazilian beaches. These locations have geological and geochemical characteristics which correspond to higher levels of natural occurring radioactivity, an example of which are the monazite sands from the Atlantic coast. The activity concentration of the sand samples from a range of beach locations in Brazil have been deduced for members of the ²³⁸U, ²³²Th and ²³⁵U decay chains, as well as the single primordial radionuclide 40K. This has been performed using a combination of destructive and non-destructive techniques in order to determine the associated radiation hazard indices which can be calculated and compared to the internationally accepted values set by the United Nations Scientific Committee on the effects of Atomic Radiation. Non-destructive measurements were carried out via γ-ray spectrometry on the unprocessed sample material. A 50% relative efficiency ORTEC GEM-FX8530-S HPGe γ-ray spectrometer, with a 0.8 mm thick carbon composite window was used to obtain spectrometric measurements from decay products within these samples. Destructive analysis was carried out using fusion methods to dissolve the samples followed by chemical separation using extraction chromatography to selectively remove the radionuclides of interest. Chemically separated samples were measured using inductively coupled plasma mass spectrometry (ICP-MS) for ²³⁸U and ²³²Th, and α-spectrometry to measure ²¹⁰Po. For alpha spectrometry it is critical that the final spectra are limited from thorium contaminants in the uranium measurements and vice versa. This is of particular importance for NORM measurements where the 4n Thorium series and 4n+2 Uranium series dominate and where interfering alphas lines in the final measurement can hinder the identification and quantification of the isotopes of interest due to spectral overlaps which result from incomplete/failed radiochemical separation. This can degrade the alpha peak spectral response and limit ultimately the achieved energy resolution. A progress report on the analysis performed to date will be presented.

Tea and coffee will be served following the seminar.