Radiochemical Separation and Quantitative Assessment of Different Radionuc/ides in Environmental samples

Abstract

Different nuclear spectroscopic teclmiques are used to detennine the specific radioactivity levels of both naturally occuning (uranium, thorium and radium-226) and anthropogenic radionuclides (Pu-238, Pu-239+240, Cs-137 and Sr-90) in different environmental and reference samples. In this study, radiochemical separation metl1ods were developed to separate tl1e natural occurring radionuclide radium-226 from botl1 uranium and thorium isotopes based on iron hydroxide precipitation at pH 8-9.Radium- 226 after being separated in each sample, was measured by gamma-spectroscopy (HPGe -well type detector) to determine the chemical recovery based on Ba-133 non isotopic radiotracer. The specific radioactivity level of Ra-226 was measured by calibrated Photo Electron Rejection Alpha Liquid Scintillation system (PERALS). Uranium and tllorium were separated from each other by using TEVA (for iliorium ) and UTEVA (for uranium) double cohunns conditioned by 3M HN03 . TI1e source preparation for boili uranium and thorium were performed by electrodepostion in acidic medium and/or micro co­ precipitation using NdF3. The chemical recoveries of both uranium and thorium isotopes were determined based on U-232 and Tit-229 radio-spikes , respectively. The chemical recovery and specific radioactivity levels of uranium and thorium were determined by calibrated alpha-spectroscopy. A standard combined meiliod was also used in this work, to separate Pu isotopes from Cs-137 and Sr-90 using TRU colunm conditioned by 8M HN03 . Pu isotopes were re-purified again and ilie Pu sources were prepared by electrodepostion for alpha spectroscopic measurements to detennine ilie chemical recovery (based on Pu-242 radiotracer) and its specific radioactivity level. Cs-137 was purified from Sr-90 by ammonium molybdophosphate (AMP). The chemical recovery (based on Cs-134 radiotracer) and specific radioactivity levels were determined by calibrated gamma­ spectroscopy (HPGe -well type detector). Sr-90 after being separated from Cs-137, was purified using crown eilier conditioned by 3M HN03 . The chemical recovery of Sr-90 in each sample was determined by gravimetric precipitation of Sr using oxalic acid at pH 8- 9 after adding Sr carrier. The specific radioactivity level of pure beta Sr-90 was determined by calibrated low level liquid scintillation counter (LSC) in beta region. The obtained results were discussed in terms of tlle equilibrium attained in ilie samples and different nuclear activities associated with different samples.