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)

Lattes

Página do item completo

Resultados de Busca

Agora exibindo 1 - 10 de 18

On the use of coincidence INAA for selenium determination
2021 - RIBEIRO JUNIOR, IBERE S.; ZAHN, GUILHERME S.; GENEZINI, FREDERICO A.; DRESCHER, ADAM; LANDSBERGER, SHELDON
Instrumental Neutron Activation Analysis (INAA) is a widely used technique applied on the determination of several elements in different matrices. Selenium is one of the elements that can be studied by INAA and its determination is usually performed using one, or both, 136:01 and 264:66 keV transitions from 75Se radioisotope. Se determination by INAA is a case that requires special attention, mainly in virtue of three issues: (i) spectral interferences may occur due to intense gamma rays from 181Hf (136 keV) and 182Ta (264 keV); (ii) in samples with high levels of K and Na, the increased background levels due to Compton effect lead to enlargement of the detection limit; (iii) high concentration of P or any other intense high-energy beta emitter can severely impact the detection below 200{300 keV due to bremsstrahlung radiation. A possible solution for these issues is the use of gamma-gamma coincidence INAA (CINAA), as the 136 and 264 keV transitions are part of a strong gamma-gamma cascade. In this work coincidence measurements of the decay of 75Se were performed to compare the results for Se obtained by conventional INAA and CINAA in biological and geological Certi ed Reference Materials (CRMs). The results show that the use of coincidence can drastically reduce the net/gross ratio, which implies in a reduction of the detection limit for 75Se; furthermore, the results of Se concentration obtained using both methodologies are in agreement with the certi ed values, and both techniques provided accurate results.
Determinação de Sm por análise por ativação neutrônica em amostras geológicas
2022 - RIBEIRO JUNIOR, IBERE S.; GENEZINI, FREDERICO A.; ZAHN, GUILHERME S.
Nesse trabalho foi desenvolvido um método alternativo para determinação do fator de interferência do 153Sm como uma função do tempo de decaimento em virtude de interferência espectral de raios-X do 239Pu. Para realizar esse estudo foram irradiados dezoito padrões sintéticos de Sm e U no reator IEA-R1. Os fatores de interferência foram determinados experimentalmente para diferentes tempos de decaimento afim de ajustar uma função/curva teórica para os dados experimentais. Ao final será introduzido uma nova possibilidade de determinação do fator de interferência para o 153Sm utilizando medidas em coincidência gama-gama que apresenta a possibilidade de eliminar as interferências dos raios-X do 239Pu.
Aplicação de técnicas de coincidência gama-gama no LFNA-CRPQ
2022 - ZAHN, GUILHERME S.; GENEZINI, FREDERICO A.; RIBEIRO JUNIOR, IBERE S.
As técnicas de coincidência γ−γ consistem no uso de mais de um detector para registrar a radiação proveniente de alguma amostra, registrando-se apenas os eventosem que fótons foram registrados em mais de um detector. Essa técnica foi trazida ao Laboratório de Física Nuclear Aplicada (LFNA-CRPq) em decorrência da experiência em trabalhos anteriores em estrutura nuclear, e permite uma redução significativa no BG dos espectros, bem como nas interferências espectrais encontradas. Neste trabalho será apresentada uma pequena introdução ao uso da técnica, bem como o estado atual de sua implementação no LFNA-CRPq, possíveis aplicações e perspectivas futuras.
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.
Comparison of two methodologies for spectra analysis in coincidence neutron activation analysis
2021 - RIBEIRO JUNIOR, I.S.; GENEZINI, F.A.; ZAHN, G.S.
The Research Reactor Center (CERPq) of IPEN-CNEN/SP has been developing a facility for Coincidence Neutron Activation Analysis (CNAA), a variation of the Neutron Activation Analysis technique in which gamma-gamma coincidence is used to reduce spectral interferences and improve detection limits of some elements. As the acquisition results in 2D-coincidence spectra, the spectrum analysis has to be dealt with accordingly. There are two distinct ways to perform these analyses, either directly, by fitting bidimensional peaks in the coincidence matrix, or by gating the spectra in one detector around each peak of interest and fitting the resulting 1D-spectrum in the usual way. In this work, the concentrations of As, Co, Cs, Sb and Se were determined in geological and biological reference materials by CNAA using two different methodologies of analysis, using the BIDIM software, which provides 2D-peak-fitting; and a combination of the AnalisaCAEN suite, which gates the 2D-spectra, with Canberra’s Genie2000, which fits the resulting unidimensional spectra. The outcomes allow for a discussion of the advantages and shortcomings of each method, both in terms of usability and of the reliability of the results.
On the use of gamma-gamma coincidence to detect very low activities
2017 - ZAHN, GUILHERME S.; GENEZINI, FREDERICO A.; RIBEIRO JUNIOR, IBERE S.; FAGIONATO, ESNEL A.
The detection of very low gamma ray activities is a delicate task, and very important in environmental radiation studies, for instance. It usually requires the use of low-background shielding, as the long counting times required usually make the background subtraction quite tricky, and often result in rather high experimental uncertainties. In this work a different approach is tested, where a two-detector gamma-gamma coincidence system is used to eliminate essentially all of the background continuum - at the cost of reduced overall efficiency and, more importantly, requiring that the radionuclide to be studied presents useful gamma-gamma coincidences. Two distinct methods of analysis are tested, either using an "open-window" coincidence where an event is registered whenever any event is registered in the other detector, or using a strict coincidence analysis, where a valid coincidence between two gamma-rays from the same decay are required; this allow for a discussion on the advantages and problems of each method, as well as for an experimental assessment of the performance of such a system.
AnalisaCAEN, a simple software suite to reduce and analyze coincidence data collected using CAEN v1724 digitizer
2019 - ZAHN, G.S.; GENEZINI, F.A.; RIBEIRO JUNIOR, I.
In this work a small software suite for the reduction and analysis of coincidence data collected using CAEN’s proprietary software was developed. These software check the output files for coincidences, generate a single list mode file with the coincident events, build histograms for each input, plus a time difference histogram and a 2-detector data matrix, perform time gates and allows for the subtraction of accidental coincidences, and perform energy gating on the final data matrices, generating histograms with the gated spectra. Moreover, the suite has an integrator that guides the user through all the required steps.
Comparison of two methodologies for spectra analysis in coincidence neutron activation analysis
2019 - RIBEIRO JR., IBERÊ S.; GENEZINI, FREDERICO A.; ZAHN, GUILHERME S.
The Research Reactor Center (CERPq) of IPEN-CNEN/SP has been developing a facility for Coincidence Neutron Activation Analysis (CNAA), a variation of the Neutron Activation Analysis technique in which gamma-gamma coincidence is used to reduce spectral interferences and improve detection limits of some elements. As the acquisition results in 2D-coincidence spectra, the spectrum analysis had to be dealt with accordingly. There are two distinct ways to perform these analyses, either directly, by fitting bidimensional peaks in the coincidence matrix, or by gating the spectra in one detector around each peak of interest and fitting the resulting 1D-spectrum in the usual way. In this work the concentrations of As, Co, Cs, Sb and Se were determined in geological and biological reference materials by CNAA using two different methodologies of analysis, using the BIDIM software, which provides 2D-peak-fitting; and a combination of the AnalisaCAEN suite, which gates the 2D-spectra, with Canberra’s Genie2000, which fits the resulting unidimensional spectra. The results allow for a discussion of the advantages and shortcomings of each method, both in terms of usability and of the reliability of the results.
Pile-up correction for coincidence counting using a CAEN 1724 digitizer
2019 - ZAHN, GUILHERME S.; RIBEIRO JUNIOR, IBERE S.; GENEZINI, FREDERICO A.
In conventional gamma-ray spectrometry, the probability of pile-up effects is considered to be proportional to the dead-time, and is usually neglected for low dead-times (below 4-5%). In gamma-gamma coincidence spectrometry, though, while the dead time takes into account only events that are actually digitized, the pile-up effects are proportional to the actual gamma-ray detection rate in each detector, not only to the ones that trigger the coincidence gate. Thus, the pile-up corrections may not be so easy to assess as in single spectrometry systems. In this work, a system composed of two HPGe detectors coupled to a CAEN v1724 digitizer is studied. A 3kBq 60Co source was analyzed, both alone and in the presence of other radioactive sources (137Cs, 133Ba and 152Eu), and the resulting coincidence peak areas were compared to assess the effectiveness of two distinct corrections: a simple normalization by the live time of acquisition and the normalization by the count rate obtained using a pulse generator. The results obtained stress the need to use the pulse generator in this specific setup in order to get accurate results.
Pile-up correction for coincidence counting using a CAEN 1724 digitizer
2017 - RIBEIRO JUNIOR, IBERE S.; ZAHN, GUILHERME S.; GENEZINI, FREDERICO A.
In conventional gamma-ray spectrometry, the probability of pile-up effects is considered to be proportional to the dead-time, and is usually neglected for low dead-times (below 4-5%). In gamma-gamma coincidence spectrometry, though, while the dead time takes into account only events that are actually digitized, the pile-up effects are proportional to the actual gamma-ray detection rate in each detector, not only to the ones that trigger the coincidence gate. Thus, the pile-up corrections may not be so easy to assess as in single spectrometry systems. In this work, a system composed of two HPGe detectors coupled to a CAEN v1724 digitizer is studied. A 3kBq 60Co source was analyzed, both alone and in the presence of other radioactive sources (137Cs, 133Ba and 152Eu), and the resulting coincidence peak areas were compared to assess the effectiveness of two distinct corrections: a simple normalization by the live time of acquisition and the normalization by the count rate obtained using a pulse generator. The results obtained stress the need to use the pulse generator in this specific setup in order to get accurate results.