Determination of uranium in tree bark samples by epithermal neutron activation analysis

Abstract

In this study uranium (U) concentrations were determined in certi ed reference materials (CRMs) and in tree bark samples collected in \Cidade Universit aria Armando de Salles Oliveira" (CUASO) USP, S~ao Paulo. The barks were collected from di erent species namely Poincianella pluviosa and Tipuana tipu. These bark samples were cleaned, dried, grated and milled for the analyses by epithermal neutron activation analysis method (ENAA). This method consists on irradiating samples and U standard in IEAR1 nuclear reactor with thermal neutron ux of 1:9 1012 n cm����2 s����1 during 40 to 60 seconds depending on the samples matrices. The samples and standard were measured by gamma ray spectroscopy. U was identi ed by the peak of 74.66 keV of 239U with half life of 23.47 minutes. Concentration of U was calculated by comparative method. For analytical quality control of U results, certi ed reference materials were analysed. Results obtained for CRMs presented good precision and accuracy, with jZ scorej 0.39. Uranium concentrations in tree barks varied from 83.1 to 627.6 ng g����1 and the relative standard deviations of these results ranged from 1.8 to 10%.