IBERE SOUZA RIBEIRO JUNIOR

IBERE SOUZA RIBEIRO JUNIOR

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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.
Uso de sistema de coincidência gama-gama associado à espectroscopia simples em medidas de análise por ativação neutrônica
2019 - RIBEIRO JUNIOR, IBERE S.
Nesse trabalho foi desenvolvido um sistema de aquisição γγ que possibilita realizar medidas de Análise por Ativação Neutrônica Instrumental por espectroscopia gama unidimensional e em coincidência simultaneamente para os elementos As, Co, Cs, La, Sc, Se e Sm. Para tal foram realizadas medidas preliminares em sistemas de aquisição γγ baseados em instrumentação analógica e digital a fim de se verificar a eficiência da técnica a partir de medições de padrões sintéticos e análises de materiais de referência certificados. Essas medidas também auxiliaram na escolha do tipo de instrumentação mais apropriada para o desenvolvimento do sistema de aquisição no Laboratório de Física Nuclear Aplicada (LFNA) do IPEN. O sistema montado no LFNA é composto de uma placa digitalizadora da marca CAEN modelo v1724 e dois detectores de germânio hiperpuro. A aquisição dos dados é controlada pelo software MC2Analyzer, que fornece dados brutos de energia e tempo dos pulsos registrados. Foram desenvolvidos dois programas de redução de dados que selecionam os eventos em coincidência a partir dos espectros unidimensionais: o DPP que prepara os dados para serem analisados em programas de análise de espectros bidimensionais; e o AnalisaCaen que trata os dados para sejam analisados em programas de análises de espectros unidimensionais. Foram realizadas análises de materiais de referência certificados biológicos e geológicos, e também padrões sintéticos utilizando-se as técnicas de Análise por Ativação Neutrônica convencional e em coincidência. Os resultados permitiram verificar a confiabilidade dos valores das concentrações dos elementos As, Co, Cs, La, Sc, Se e Sm obtidos com o sistema de coincidência desenvolvido. Os resultados obtidos por ambas as técnicas, Análise por Ativação Neutrônica Convencional e Análise por Ativação Neutrônica em Coincidência, foram comparados e valiados em termos de precisão e exatidão pelo critério de Enscore. Em alguns casos, os resultados de concentração obtidos por meio das medidas de coincidência forneceram melhores do que os resultados obtidos pela espectroscopia gama convencional.
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.
Hyperfine interactions in Pd foils during D/H electrochemical loading
2016 - SILVA, ERIC B. da; CORREIA, JOAO G.; ZOGHBY, MICHEL; GAHL, JOHN; SCHELL, JULIANA; MATOS, IZABELA T. de; RIBEIRO JUNIOR, IBERE S.; CARBONARI, ARTUR W.; HUBLER, GRAHAM K.; VIOLANTE, VITTORIO; THIOYE, MOUSTAPHA; HE, JINGHAO
The Fleischmann and Pons Effect (FPE) is the appearance of anomalous excess heat during electrolytic loading of hydrogen in metal. Although observed well above measurement uncertainties [1] this effect still remains unexplained. Unlike previous studies where hydrogen (H) was pre-loaded before Time Differential Perturbed Angular Correlations (TDPAC) [2,3] was performed, this present work probes, at the nanoscopic scale, palladium (Pd) samples during H and deuterium (D) loading in 0.1M LiOH or LiOD electrolyte. Radioactive 181Hf (181Ta) was implanted at 80 keV (HISKP-Bonn) and experiments were performed at the ISOLDE-CERN SSP laboratories after vacuum annealing to recover implantation defects. An almost “flat” unperturbed PAC – R(t) spectrum was observed, as expected for Hf/Ta atoms at cubic Pd sites with no remaining point defects in their vicinity. Upon D loading the “flat” unperturbed R(t) spectrum changes to a characteristic Gaussian-like EFG distribution, centered near zero EFG, due to the random distribution of D atoms inside the Pd lattice. With increasing D concentration, the central value of the distribution becomes nonzero, thus revealing that the Pd crystalline structure is relaxed from cubic, consistent with the phase diagram for Pd hydrides. The data also shows that, while being an impurity in the system under study, the Hf/Ta atoms do not trap nor significantly interfere with the H/D atoms in the Pd lattice that would bias the present studies. Thus, further experiments aimed at studying the FPE under external excitations are envisaged.
On neutron activation analysis with gamma gamma coincidence spectrometry
2017 - ZEISLER, ROLF; CHO, HANA; RIBEIRO JUNIOR, IBERE S.; SHETTY, MARTIN G.; TURKOGLU, DANYAL
A new gamma gamma coincidence system has been set up at NIST. It is operated with a digital data finder supported by new software developed at NIST. The system is used to explore possible enhancements in instrumental neutron activation analysis (INAA) and study applicability to neutron capture prompt gamma activation analysis (PGAA). The performance of the system is tested with certified reference materials for efficiency calibration and quantitative performance. Comparisons of INAA results based on conventional gamma-ray spectrometry data with INAA results based on coincidence data obtained from the same samples show improvements in the counting uncertainties and demonstrates the quantitative accuracy of the new system.
In and Cd as defect traps in titanium dioxide
2017 - SCHELL, JULIANA; LUPASCU, DORU C.; CORREIA, JOAO G.M.; CARBONARI, ARTUR W.; DEICHER, MANFRED; BARBOSA, MARCELO B.; MANSANO, RONALDO D.; JOHNSTON, KARL; RIBEIRO JUNIOR, IBERE S.
We present a study of TiO2 single crystals from the point of view of the dopant atom that simultaneously behaves as the probing element. We used gamma-gamma time dependent perturbed angular correlations working with selected tracer elements (In-111/Cd-111, Cd-111m/Cd-111) together to investigate the different behavior of Cd and In dopants, particularly their interaction with point defects in the TiO2 lattice. Results show that the hyperfine interactions observed at Cd-111 from In-111 or Cd-111m decay are quite different. In-111/Cd-111 results show a single site fraction characterized by a quadrupole frequency with asymmetry parameter similar to those observed for the same probe nuclei in bulk TiO2 oxides. Results for Cd-111m/Cd-111 reveal two site fractions, one characterized by the same hyperfine parameters to those measured in bulk TiO2 and another fraction characterized by a quadrupole frequency and asymmetry parameters with higher values, as observed in thin TiO2 films and correlated with point defects. The results are discussed emphasizing the differences for Cd and In as defect traps on TiO2.
Ion implantation in titanium dioxide thin films studied by perturbed angular correlations
2017 - SCHELL, JULIANA; LUPASCU, DORU C.; CARBONARI, ARTUR W.; MANSANO, RONALDO D.; RIBEIRO JUNIOR, IBERE S.; DANG, THIEN T.; ANUSCA, IRINA; TRIVEDI, HARSH; JOHNSTON, KARL; VIANDEN, REINER
The local environment in titanium dioxide was studied by the time dependent perturbed gamma-gamma angular correlation of In-111/Cd-111 and Hf-181/Ta-181 at the Helmholtz-Institut fur Strahlen-und Kernphysik, Bonn. An introduction to the implantation methodologies performed at the Bonn Radioisotope Separator is presented. The investigation was carried out on thin films, which were deposited by magnetic sputtering on Si. The results show two different sites for both probe nuclei with unique electric quadrupole interaction. Using Cd-111 one of them has been attributed to the substitutional Ti at the rutile structure. For Ta-181, the spectra show the anatase phase, with a well-defined electric quadrupole frequency.