ROBINSON ALVES DOS SANTOS

ROBINSON ALVES DOS SANTOS

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A comparative study on the performance of radiation detectors from the HgI2 crystals grown by different techniques
2011 - MARTINS, J.F.T.; COSTA, F.E.; SANTOS, R.A.; MESQUITA, C.H.; HAMADA, M.M.
There have been attempts to develop room-temperature X- and gamma ray semiconductor detectors for various applications. The main physical semiconductor properties required for fabrication of room temperature semiconductor detectors are: (1) high atomic number; (2) high density; (3) high absorption coefficient; (4) a band gap large enough to keep leakage currents low, at room temperature and (5) large electron and hole mobility-lifetime products, for an efficient charge collection [1, 2]. Among these types of detectors, HgI2 has emerged as a particularly interesting material in view of its wide band gap (2.13 eV) and its large density (7.5 g/cm3 ). HgI2 crystals are composed of high atomic number elements (ZHg=80 and Zi=53) and with high resistivity (>1014 ficm). These are important factors in applications where compact and small thickness detectors are necessary for X- and gamma rays measurements. However, the applications of Hgi2 are limited by the difficulty in obtaining high-quality single crystals and the long-term reliability problems in devices made from crystals [1]. in this work, the Hgi2 crystals were grown using four different techniques: (a) physical vapor transport, (b) solution from dimethyl sulfoxide complexes, (c) vapor growth of HgI2 precipitated from acetone and (d) Bridgman method. The obtained crystals for four methods were characterized considering the following physical chemistry properties: crystal stoichiometry, crystal structure, plan of the crystal orientation, surface morphology of the crystal and crystal impurity. The influence of these physical chemistry properties on the crystals developed by four techniques was studied, evaluating their performance as a radiation detector. The best result of radiation response was found for the crystal grown by physical vapor transport. Also, the dependence of the radiation response on the HgI2 crystal purity was also studied. For this, the HgI2 raw material was purified by the many pass zone refining technique. A significant improvement in the characteristics of the detector-crystal was achieved, when the starting materials became purer.
Purification and crystal growth of the bismuth (III) iodide-influence of trace impurities on the crystal quality
2017 - FERRAZ, CAUE de M.; ARMELIN, MARIA J.A.; OLIVEIRA, RENE R.; OTUBO, LARISSA; MARTINS, JOAO F.T.; SANTOS, ROBINSON A. dos; COSTA, FABIO E.; CARVALHO, DIEGO V.S.; OMI, NELSON M.; MESQUITA, C.H.; HAMADA, MARGARIDA M.
This work describes the experimental procedure of purification and preparation of BiI3 crystals by Repeated Vertical Bridgman technique, aiming a future application of this semiconductor crystal as a room temperature radiation detector. The BiI3 powder used as raw material was purified three times and, at each purification, the crystal was evaluated by systematic measurements of the reduction of the impurities, crystalline structure, stoichiometry and surface morphology. The reduction of the trace metal impurities in the BiI3, at each purification, was analyzed by Instrumental Neutron Activation Analysis (INAA), in order to evaluate the efficiency of the purification technique established in this work. It was demonstrated that the Repeated Bridgman technique is effective to reduce the concentration of many impurities in BiI3, such as Ag, As, Br, Cr, K, Mo, Na and Sb. The crystalline structure of the BiI3 crystal purified twice and three times was similar to BiI3 pattern. However, for BiI3 powder and purified once, an intensity contribution of the BiOI was observed in the diffractograms. Improvement in the stoichiometric ratio was observed at each purification step, as well as the crystal surface morphology.
Influence of impurities on the radiation response of the TlBr semiconductor crystal
2017 - SANTOS, ROBINSON A. dos; MESQUITA, CARLOS H. de; SILVA, JULIO B.R. da; FERRAZ, CAUE de M.; COSTA, FABIO E. da; MARTINS, JOAO F.T.; GENNARI, ROSELI F.; HAMADA, MARGARIDA M.
Two commercially available TlBr salts were used as the rawmaterial for crystal growths to be used as radiation detectors. Previously, TlBr salts were purified once, twice, and three times by the repeated Bridgmanmethod. Thepurification efficiency was evaluated by inductively coupled plasma mass spectroscopy (ICP-MS), after each purification process. A compartmental model was proposed to fit the impurity concentration as a function of the repetition number of the Bridgman growths, as well as determine the segregation coefficients of impurities in the crystals. The crystalline structure, the stoichiometry, and the surface morphology of the crystals were evaluated, systematically, for the crystals grown with different purification numbers. To evaluate the crystal as a radiation semiconductor detector, measurements of its resistivity and gamma-ray spectroscopy were carried out, using 241Am and 133Ba sources. A significant improvement of the radiation response was observed in function of the crystal purity.
Multi-elemental segregation analysis of thallium bromide impurities purified by the repeated bridgman technique
2012 - SANTOS, ROBINSON A. dos; SILVA, JULIO B.R. da; GENNARI, ROSELI F.; MARTINS, JOAO F.T.; FERRAZ, CAUE de M.; HAMADA, MARGARIDA M.; MESQUITA, CARLOS H. de
Mercuric iodide semiconductor detectors encapsulated in polymeric resin
2015 - MARTINS, JOAO F.T.; SANTOS, ROBINSON A. dos; FERRAZ, CAUE de M.; OLIVEIRA, ADRIANO S.; VELO, ALEXANDRE F.; DISH, CRISTIAN; MESQUITA, CARLOS H. de; FIEDERLE, MICHAEL; HAMADA, MARGARIDA M.
Influence of impurities on the surface morphology of the TlBr crystal semiconductor
2013 - SANTOS, ROBINSON A. dos; SILVA, JULIO B.R. da; MARTINS, JOAO F.T.; FERRAZ, CAUE de M.; COSTA, FABIO E. da; GENNARI, ROSELI F.; MESQUITA, CARLOS H. de; HAMADA, MARGARIDA M.
A comparative study on surface morphology from the HgIsub(2) semiconductors prepared by different techniques
2013 - MARTINS, JOAO F.T.; FERRAZ, CAUE de M.; SANTOS, ROBINSON A. dos; MESQUITA, CARLOS H. de; MIRANDA, MARGARIDA M.
Multielementar segregation analysis of the thallium bromide impurities purified by repeated bridgman technique
2011 - SANTOS, ROBINSON A. dos; COSTA, FABIO E. da; GENNARI, ROSELI F.; MARTINS, JOAO F.T.; MARCONDES, RENATA M.; MESQUITA, CARLOS H. de; HAMADA, MARGARIDA M.
A comparative study on the performance of radiation detectors from the HgIsub(2) crystals grown by different techniques
2012 - MARTINS, JOAO F.T.; COSTA, FABIO E.; SANTOS, ROBINSON A. dos; MESQUITA, CARLOS H. de; HAMADA, MARGARIDA M.
Purification of HgISUB(2) crystals from physical vapor transport for application as radiation detectors
2012 - MARTINS, JOAO F.T.; SANTOS, ROBINSON A. dos; COSTA, FABIO E. da; MESQUITA, CARLOS H. de; HAMADA, MARGARIDA M.