GUILHERME SOARES ZAHN

GUILHERME SOARES ZAHN

(Fonte: Lattes)

Resumo

Has a bachelor's degree in Physics from Universidade de São Paulo (1991), master's at Nuclear Engineering from Universidade de São Paulo (1994) and doctorate at Nuclear Engineering from Universidade de São Paulo (2006). Has experience in nuclear ans applied physics, focusing on nuclear structure, acting on the following subjects: beta decay, neutron activation, gamma spectroscopy, nuclear structure, neutron flux determination and detection, and also on the development od instrumentation and sotware aimed at nuclear applications. (Text obtained from the Currículo Lattes on October 14th 2021)

Possui graduação em Física pela Universidade de São Paulo (1991), mestrado em Tecnologia Nuclear pela Universidade de São Paulo (1994) e doutorado em Tecnologia Nuclear pela Universidade de São Paulo (2006). Atualmente é pesquisador da Comissão Nacional de Energia Nuclear, lotado no Centro do Reator de Pesquisas do Instituto de Pesquisas Energéticas e Nucleares. Tem experiência na área de Física Nuclear, com ênfase em Estrutura Nuclear, atuando principalmente nos seguintes temas: decaimento beta, detecção de nêutrons, irradiadores de nêutrons, ativação neutrônica, fluxo de nêutrons, desenvolvimento de instrumentação e de software para aplicações nucleares. (Texto extraído do Currículo Lattes em 14 out. 2021)

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Examination of Natural Radioactivity Concentration and Radiological Exposure of Soil Within Mining Site in Umuahia South Abia State Nigeria, Using High Purity Germanium (HPGe) Gamma Ray Spectrometry
2023 - ONUDIBIA, MOSES E.; SILVA, PAULO S.C. da; ESSIETT, ANIESUA A.; ZAHN, GUILHERME S.; GENEZINI, FREDERICO A.; IMEH, EDET E.; NNAMANI, NGENE C.; OGODO, ALLOYSIUS C.; MFOM, CELESTIAL B.; OKOH, FRANCA O.
Mining activity is one of the major sources of exposure to radiation. The main goal of this study was to determine the natural radioactivity level and its radiological exposure risk in mining site Umuahia South Abia State, Nigeria, using High Purity Germanium (HPGe) gamma ray spectrometry. The activity concentration of 40K, 226Ra and 232Th in the soil ranges from 31±2 to 367±27 Bq kg-1, with mean value of 142±11 Bq kg-1; from 26±2 to 65±5 Bq kg-1, with mean value of 49±4; and from 53±9 to 109±17 Bq kg-1, with mean value of 77±16 Bq kg-1, respectively. The activity concentrations of 226Ra and 232Th are above the global values of 32 and 45 Bq kg-1 while 40K is depleted in relation to the global mean of 412 Bq kg-1. Radiological parameters are generally in agreement with the values observed for other Nigerian and other countries soil reported in literature. The main responsible for the values observed for the radiological parameters is 232Th followed by 226Ra. The use of this soil for dwelling construction is unlikely to pose any radiological harm for the residents.
Radioactivity concentration and radiological effect of soil from Umuahia Abia State, Nigeria
2022 - ONUDIBIA, M.E.; SILVA, P.S.C.; ESSIETT, A.A.; ZAHN, G.S.; GENEZINI, F.A.
Determination of scale factor for Ni-59 and Ag-108m in ion exchange resin from Angra 1
2021 - RIBEIRO JUNIOR, I.S.; GENEZINI, F.A.; SILVA, P.S.C. da; ANGELINI, M.; JUNQUEIRA, L.S.; ZAHN, G.S.
Evaluation of the maximum emitting layer of Rn-222 in cementitious building materials
2019 - CORREA, J.N.; PASCHUK, S.A.; BARRETO, R.C.; DENYAK, V.; SCHELIN, H.R.; NARLOCH, D.C.; DEL CLARO, F.; HASHIMOTO, Y.; MATIN, A.C.; SILVA, A.C.M.; ZAHN, G.S.; SILVA, P.S.C.
Introduction – Radionuclides present in construction materials are of interest in the view of environmental radioactivity. The limitations established have focused on the concentration of Ra-226 and the consequent exhalation of Rn-222. A physical/mathematical model developed at the Laboratory of Applied Nuclear Physics (LFNA/UTFPR) correlates the exhaled Rn-222 with the Ra-226 inherent to the material. The model considers the exhalation of Rn-222 by a plane surface that simulates exhalation in fl oors, walls and ceilings. Determination of the maximum emitting layer of Rn-222 that effectively exhales is important to support the model. The objective of this research is to determine the maximum emissive layer of Rn-222 that provides internal diffusion and exhalation of radon-222 in cementitious materials. Methods - Cylindrical samples were made of common cement paste and cement paste with sand of high Ra-226 concentration. The samples (thicknesses 1 to 5 cm) were sealed in order to ensure the exhalation of Rn-222 through one surface. Samples and diffusion chambers containing CR-39 solid-state detectors were inserted into a glass vessel. The samples/detectors were stored for 30 days. Subsequently, the detectors were chemically etched and the nuclear tracks in the CR-39 detectors were counted. Results – For each type of sample a curve was fi tted whose threshold indicated the maximum emitting layer. The results obtained on the samples of common cement paste indicated a maximum emitting layer of 2cm. For samples of cement paste with sand with high Ra-226 concentration, no threshold was observed, indicating that the maximum emitting layer is greater than 5cm. Conclusions - The maximum emitting layer thickness of Rn-222 of common materials determined by curve fi tting was 2cm. For materials with high concentration of Ra-226 there is an indication that the emitter layer is larger than 5cm. The obtained results subsidize the physical/mathematical model developed in the LFNA/UTFPR.
On the feasibility of producing Lu-177 in the IEA-R1 reactor via the direct route
2019 - GENEZINI, FREDERICO A.; ZAHN, GUILHERME S.; SILVA, PAULO S.C. da; NORY, RENATA M.; MOREIRA, EDSON G.; SANTIAGO, PAULO S.
Over the last years the 177Lu radioisotope has attracted great interest for the use in therapeutic and diagnostic procedures simultaneously, being what is now called a theranostic radioisotope. There are mainly two ways of producing this radioisotope, by direct neutron capture in a 176Lu target (the \direct route") or by irradiating a 176Yb sample, producing 177Yb that will then decay to 177Lu (also referred as the \indirect route"). In this work the feasibility of producing 177Lu in the IEA-R1 nuclear reactor via the direct route was assessed, and the speci c activity that could be obtained was estimated both experimentally and theoretically, allowing for a discussion on the feasibility of commercially producing 177Lu by 176Lu neutron capture in the IEA-R1 reactor.
External gamma exposure due to the application of carbonate niobium tailing as soil amendment
2019 - AYLLON, RAFAELLA M.; TORRECILHA, JEFFERSON K.; SAUEIA, CATIA H.R.; NISTI, MARCELO B.; TORQUATO, HENRIQUE; EL HAJJ, THAMMIRIS M.; ZAHN, GUILHERME S.; SILVA, PAULO S.C. da
The storage of tailing from anthropic activities like mining, which may contain radionuclides, is a problematic situation consequent from NORM industries and for which alternatives should be sought. This paper presents the preliminary results for the use of a carbonate tailing derived from niobium extraction as soil amendment from the point of view of the radiological indices, since this material is a NORM residue. The activity concentration of radionuclides 226Ra, 228Ra and 40K were determined in six samples of carbonate by gamma spectrometry and the radiological hazard indices were calculated for the carbonate itself and simulated for soil application. The results indicated that the dilution of the carbonate in the soil do not increase the radiological hazard indices.
Application of semi-empirical model for the evaluation of radium activity in phosphogypsum used as component of clinker
2019 - GERALDO, RICARDO R.; PASCHUK, SERGEI A.; BARRETO, RAFAEL C.; ZAHN, GUILHERME S.; SILVA, PAULO S.C. da; SILVA, AMANDA C.M.da; NARLOCH, DANIELLE C.; ARAUJO, ISABELLE C.
Phosphogypsum is a residue that has been used by the cement industry as a substitute for the natural gypsum, used as a clinker additive during the production of Portland cement. There is a potential increase in this residue use since the large amount of phosphogypsum is generated as outcome of the phosphate fertilizer industries. However, phosphogypsum can be considered a source of radioactive contamination since it has 226Ra in its composition. Depending on the concentration of 226Ra, from the radiological protection point of view, this may cause a problem because this radionuclide and its direct decay product 222Rn along with other decay products, represent the largest fraction of radiation internal dose received by people. In order to evaluate the level of radiological risk that may be associated with the use of phosphogypsum, it is necessary to identify the concentration of 226Ra in building material. The aim of this research is to analyze the samples of phosphogypsum in relation to the concentrations of 226Ra, determined indirectly through 222Rn activity measurements. This measurement process has the advantage of being fast, convenient and relatively inexpensive when compared to traditional 226Ra concentration in samples measurement methods. Proposed physical-mathematical model was used to establish radium concentration from radon exhalation rate from cement mortar samples. The 222Rn activity measurements were performed with a portable detector with cubic phosphate samples with dimensions of 50x50x50mm3 allocated in a closed atmosphere of sampling chamber until secular equilibrium was reached. Obtained concentrations of radium activity in studied samples of phosphogypsum and cement mortars were found below the limits recommended by CNEN and international regulation.
Radionuclide analysis of the IEA-R1 pool water
2019 - TICIANELLI, REGINA B.; ZAHN, GUILHERME S.; SILVA, PAULO S.C. da; GENEZINI, FREDERICO A.
IEA-R1 is a 5MW pool-type research reactor built in the late 1950's. In the last years, it operates at 4.5MW for 8h on Mondays, Tuesdays and Wednesdays. In every day of operation, a sample is taken from the pool water both before starting the reactor and at the end of the day and analyzed in an HPGe detector, in order to verify for possible problems with the fuel elements or other issues. In this work, the results obtained in these analyses spanning for some months are discussed regarding the radionuclides frequently identi ed and the dependence of their activities with time.
Determination of I-129 on radioactive waste from Angra 1 and 2 Power Plants
2019 - JUNQUEIRA, LUCAS S.; ANGELINI, MATHEUS; ZAHN, GUILHERME S.; SILVA, PAULO S.C. da
Radioactive waste must be characterized in order to be deposited in a suitable place for its confinement, avoiding any contamination of the environment. This study determined 129I, one of the difficult-to-measure nuclides that make up the radioactive waste from Angra 1 and 2 nuclear power plants. The methodology used a 129-I (1Bq/mL) liquid certified standard and consisted on guarantying that all the iodine was converted into iodide before the addition of PdCl2 for the precipitation of PdI2. After the separation procedure the 129I was quantified by gamma spectrometry by measuring its X-ray emissions with energies of 29.7 keV and 33.8 keV, as well as the gamma-ray emission of 39.6 keV. The chemical yield of the procedure was 74.4% (0,2).
Ni-59 determination by measurement of annihilation energy
2019 - JUNQUEIRA, LUCAS S.; ZAHN, GUILHERME S.; SILVA, PAULO S.C. da
Radioactive waste is subject to regulations regarding its inventory, transportation and final deposition. Such standards require the knowledge of the tailing contents in a way that is possible to accommodate them in a repository capable of containing their radiation completely. In this study a methodology was established for determining the concentration of 59Ni using the annihilation energy (0.511 MeV) between a positron from its + emission, and an electron that is widely present in matter. To ensure the reliability of the methodology, the area of the annihilation peak was compared to 59Ni Kα and Kβ x-ray peaks. To make this method viable the separations of Ni from the other components of the sample was necessary. This was done by using dimethylglyoxime (DMG) for Ni precipitation. Of all the Ni radioisotopes only 59Ni have a half-life longer than a few days, so that 59Ni can be determined without radioisotopical interferences. After precipitation with DMG, the substrate was vacuum filtered on filter paper, using an apparatus to preserve the geometry of the precipitate in different samples. The 59Ni precipitate was then counted in an extended range gamma spectrometer and the 511 keV peak compared to the Ni x-rays in order to verify the reliability of the method.