NICOLE PEREIRA DE LIMA
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Artigo IPEN-doc 25757 Determination of uranium in tree bark samples by epithermal neutron activation analysis2019 - LIMA, N.P.; SAIKI, M.In this study uranium (U) concentrations were determined in certified reference materials (CRMs) and in tree bark samples collected in “Cidade Universitária Armando de Salles Oliveira” (CUASO) USP, São Paulo. CRMs were analyzed using the experimental conditions used for barks for analytical quality control of U determina-tion. The barks were collected from different species namely Poincianella pluviosa and Tipuana tipu. These bark samples were cleaned, dried, grated and milled for the analyses by epithermal neutron activation analysis meth-od (ENAA). This method consists on irradiating CRMs, samples and U standard in IEA-R1 nuclear reactor with thermal neutron flux of 1.9 x 1012 n cm-2 s-1 during 40 to 60 seconds depending on their matrices. The U was iden-tified, using gamma-ray spectrometry, by the peak of 74.66 keV of 239U with half-life of 23.47 minutes. Concen-tration of U was calculated by comparative method. Results obtained for CRMs presented good precision and accuracy, with |Z score| ≤ 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 %.Resumo IPEN-doc 24563 Determination of uranium in tree bark samples by epithermal neutron activation analysis2017 - LIMA, N.P.; SAIKI, M.It is well known that uranium is a toxic element to human beings and it is considered as an environmental pollutant. This element presents accumulative property and can be concentrated on the organs causing various types of diseases. Uranium is widely distributed in the environment, so it is of great interest to improve the method of neutron activation analysis to be applied in its determinations in tree barks used as environmental pollution biomonitor. For analytical quality control of the U results, certified reference materials (CRMs) were analyzed. The tree bark samples were collected from the Tipuana tipu (Tipuana) and Poincianella pluviosa (Sibipiruna) species and, for the analyses the outer layer of the bark was grated and then ground to obtain a powder. Aliquots of CRMs or tree bark samples were weighed in polyethylene envelopes and, irradiated together with U synthetic standard, inside a Cd capsule for epithermal neutron activation analysis (ENAA). The irradiation was performed a pneumatic transfer system at the IEA-R1 nuclear research reactor at IPEN - CNEN/SP. The thermal neutron flux used was of 1:9 1012 n cm2s1 and the irradiation time was of 60 seconds. After adequate decay time, the sample and U standard were measured using a HGe detector coupled to a digital spectrum analyzer DSA 1000, both from Canberra. Uranium was identified by gamma ray peak of 74.66 keV of 239U and half-life of 23.47 minutes. The concentration of U was calculated by comparative method. A total number of five CRMs were analyzed and its results presented relative standard deviations lower than 13.4%, relative errors lower than 3.1% and |Z score| values lower than 0.29. Results obtained in the analyses of tree barks varied from 81.8 to 222.1 ng/g, indicating that U concentrations in the analyzed samples were very low.Artigo IPEN-doc 24068 Determination of uranium in tree bark samples by epithermal neutron activation analysis2017 - LIMA, NICOLE P. de; SAIKI, MITIKOIn 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 cm2 s1 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 g1 and the relative standard deviations of these results ranged from 1.8 to 10%.