Studies of naturally occurring radioactive materials by direct gamma-ray spectrometry and after chemical separation

Naturally occurring radioactive materials (NORM) have been present in our environment since the creation of the earth. The 232 Th, 235U and 238U radionuclides and their decay products are of much interest among the NORM because their emission of alpha- and/or beta-rays could be hazardous to living tissues.;One of the objectives of this thesis was to develop reliable methods for the determination of NORM by gamma-ray spectrometry. The first approach involved direct gamma-ray spectrometry and the reduction of the natural background radioactivity to improve detection limits. The efficacy of adding a lead shield surrounding the gamma-ray spectrometer and a Compton suppression system (CSS) to reduce background activity was assessed. The activities of 228Ac, 228Th, 212Pb, 212Bi, and 208 TI radionuclides belonging to the 232Th decay series; 234Th, 234Pa, 230Th, 214Pb, 214Bi, and 210TI from the 238U decay series, and 235U, 231Th, 231Pa, 227Th, 223Ra and 211Pb of the 235U decay series were measured in water samples and food items using this method. The lowest minimum detectable activity of 1.2 mBq was obtained for 212Pb.;To further improve the detection limits, a pseudo-cyclic epithermal instrumental neutron activation analysis (PC-EINAA) method in conjunction with CSS was developed for the determination of uranium in food items with a detection limit of 0.05 mug g-1. A separation method for uranium and thorium was used to improve the detection limits obtained by PC-EINAA-CSS using a coprecipitation step followed by a separation step using TEVA.Resin and TRU.Spec resins in tandem. The detection limits for thorium and uranium are 2 and 0.8 ng g-1, respectively. The method was applied to food items and drinking water.;Both precision and accuracy of all methods were found to be very good. The expanded uncertainties associated with the determination of activities and concentrations of NORM by gamma-ray spectrometry were studied. The relative standard uncertainties (RSU) were found to range from 6 to 30% with an average of 15% in direct gamma-ray spectrometry of the radionuclides mentioned above. The RSU for uranium in reference materials was observed to vary from 2.3 to 4.2% by PC-EINAA-CSS and to improve to 1.4% by the separation methods developed.