JOAO PAULO DA SILVA ALVES
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Resumo IPEN-doc 30299 Scintillation characteristics of pure cesium iodide crystals and doped with Tl+, Br- and Li+ ions for use as radiation detectors2023 - PEREIRA, MARIA da C.C.; MADI FILHO, TUFIC; BERRETTA, JOSE R.; ALVES, JOAO P. da S.In recent years, more attention has been devoted in the discovery of new scintillators or to improve the characteristics of known scintillators. Today inorganic scintillators are exploited in many new fields such as positron emission tomography (PET) computerized X-ray tomography, space physics and astronomy. Inorganic crystals are the scintillators most commonly used for the detection of gamma rays, X-rays and thermal neutrons. CsI:Tl, CsI:Br, CsI:Li and pure CsI crystals were grown in our laboratory using the vertical Bridgman technique. The concentrations of dopants ranged from 10-1M to 10-4M. The intentional introduction of a certain ion into a crystal depends on physical and chemical properties, that is, the dopant and the matrix. In physical terms, there is a limitation on the volume of ions that can in principle be introduced into the crystal lattice. Furthermore, any substitutional arrangement must preserve the electrical neutrality of the crystal. In chemical terms, one must consider which dopant will accumulate in the phase in which its introduction results in a smaller increase in the free energy of the system. This parameter is represented by the impurity segregation coefficient. It was observed that the wavelength of maximum luminescence emission is characteristic for each crystal. Pure cesium iodide crystal showed maximum intensity of luminescence at the wavelength of 320 nm. The CsI:Tl crystal showed luminescence at a wavelength of 540 nm. CsI:Br and CsI:Li crystals showed maximum luminescence around 420 nm. Analyses were carried out to evaluate the scintillators concerning neutron radiation from AmBe source, with energy range of 1 MeV to 12 MeV. The activity of the AmBe source was 1Ci Am. The fluency was 2.6 x 106 neutrons / second. The crystals response gamma radiation was evaluated in the energy range of 355keV to 1333 keV. In this work, the main optical properties of pure and doped CsI with different ions were studied in order to understand the scintillation mechanism and its application in devices that use the principle of scintillation to detect radiation.Resumo IPEN-doc 30152 Response of CsI:Pb scintillator crystal to neutron radiation2023 - PEREIRA, MARIA da C.C.; MADI FILHO, TUFIC; BERRETTA, JOSE R.; ALVES, JOAO P. da S.The helium-3 world crisis requires a development of new methods of neutron detection to replace commonly used 3He proportional counters. In the past decades, great effort was made to developed efficient and fast scintillators to detect radiation.[1] These detectors should, then, be carefully characterized both experimentally and by means of advanced simulation code. Ideally, the detector should have the capability to separate neutron and gamma induced events either by amplitude or through pulse shape differences. As neutron sources also generate gamma radiation, which can interfere with the measurement, it is necessary that the detector be able to discriminate the presence of such radiation. Considerable progress has been achieved to develop new inorganic scintillators, in particular increasing the light output and decreasing the decay time by optimized doping. Crystals may be found to suit neutron detection. In this report, we will present the results of the study of lead doped cesium iodide crystals (CsI:Pb) grown in our laboratory, using the vertical Bridgman technique. The concentration of the lead doping element (Pb) was studied in the range 5x10-4M to 10-2M. The crystals grown were subjected to annealing (heat treatment). In this procedure, vacuum of 10-6 mbar and continuous temperature of 350°C, for 24 hours, were employed. In response to neutron radiation, an AmBe source with energy range of 1 MeV to 12 MeV was used. The activity of the AmBe source was 1Ci Am. The fluency was 2.6 x 106 neutrons/second. The operating voltage of the photomultiplier tube was 1300 V; the accumulation time in the counting process was 600 s and 1800 s. The scintillator crystals used were cut with dimensions of 20 mm diameter and 10 mm height. The Monte Carlo method was used to determine the neutron flux arriving in the detector and the calculated values were obtained by means of MCNP code.Artigo IPEN-doc 28299 Growth of scintillating bromide-doped cesium iodide crystals for radiation detection2021 - ALVES, J.P.S.; M.FILHO, T.; PEREIRA, M.C.C.