D.N. Souza

Influence of thermal treatment on the Raman, infrared and TL responses of natural topaz

Abstract Analyses of thermoluminescence (TL) and thermally stimulated exoelectron emission have proved that the natural Brazilian topaz is a promising material for dosimetry of ionizing radiation. Topaz is an aluminum fluorosilicate with a general composition of Al 2 (SiO 4 )(F,OH) 2 whose main defect is the presence of OH − groups substituting for the F − ions. Analyses of topaz samples from Santo Antonio do Jacinto, MG, Brazil, showed that their TL responses are strongly affected by the temperature of pre-irradiation thermal treatment. This behavior was correlated to the changes observed in the infrared and Raman spectra and a model could be proposed for the charge trapping and recombination process in colourless topaz.

Thermoluminescence of brazilian topaz

Abstract Thermoluminiscence measurements were performed on samples of yellowish Brazilian Topaz from Acari, MG. Virgin samples revealed peaks 2 and 4 at about 150 and 300°C. respectively, while in samples with extra dose of y-rays, we observed another peak at 80°C. When topaz samples were thermally treated, peak 4 vanished and peak 3 at about 180°C, became visible. Isothermal decay of peak 2 performed on virgin samples showed that peak 3 is present on this samples too. The spectra of the first 3 peaks are very similar in the range of 350 to 500 nm indicating that the recombination processes related to these 3 peaks could be the same. The dose dependency of the TL intensity of the first 3 peaks was mesured from 0.5 to 400 Gy and it sems to start saturating above 400 Gy.

Evaluation of doses in radiotherapy using solid-state composites based on natural colourless topaz

The thermoluminescent properties of composites containing powdered topaz embedded in Teflon or glass were studied and compared with the corresponding properties of the well known TLD-100 commercial dosimeters. Relative sensitivity, TL fading, reproducibility of the sample preparation process, and possibility of re-utilisation of the dosimeters were investigated. Measurements of absorbed doses in simulated radiotherapy treatments were also taken. The irradiations were performed using gamma rays from a 60Co source in the dose range from 1cGy to 2Gy. The dosimeters were installed in badges and attached inside acrylic plates of various thicknesses in the radiation fields. The dose profiles obtained with this procedure are very similar to the ones obtained with equivalent tissues. It is concluded that these composites of natural colourless topaz crystals can be efficiently used as TL dosimeters.

The use of pellets of brazilian natural topaz as radiation dosimeters

Abstract The properties of the thermoluminescent emission (TL) and thermally stimulated exoelectron emission (TSEE) of pellets of colourless natural topaz samples from Santo Antonio do Jacinto, Minas Gerais, Brazil, were studied with the aim of use as solid state dosimeters. Standardized fields of 60Co, 137Cs, 241Am, 90Sr/90Y and X-rays were used for the tests. The TSEE and TL responses were studied as a function of the radiation energy (photons and particles) and as a function of the absorbed dose. The results indicate that colourless topaz from Minas Gerais, Brazil, is a promising material for dosimetric purposes.

A atual situação da braquiterapia de alta taxa de dose em colo do útero realizada no Brasil

Objective To assess the current situation of high-dose-rate (HDR) brachytherapy for cancer of the cervix in Brazil, regarding apparatuses, planning methods, prescription, fractionation schedule and evaluation of dose in organs at risk. Materials and Methods In the period between March/2012 and May/2013, a multiple choice questionnaire was developed and sent to 89 Brazilian hospitals which perform HDR brachytherapy. Results Sixty-one services answered the questionnaire. All regions of the country experienced a sharp increase in the number of HDR brachytherapy services in the period from 2001 to 2013. As regards planning, although a three-dimensional planning software was available in 91% of the centers, conventional radiography was mentioned by 92% of the respondents as their routine imaging method for such a purpose. Approximately 35% of respondents said that brachytherapy sessions are performed after teletherapy. The scheme of four 7 Gy intracavitary insertions was mentioned as the most frequently practiced. Conclusion The authors observed that professionals have difficulty accessing adjuvant three-dimensional planning tools such as computed tomography and magnetic resonance imaging.

Measurement of Single Scan Dose Profiles in CT Using a Commercial Photodiode

Computed tomography (CT) is a significant source of medical X-ray for the general population. As an alternative method to the 100 mm long ionization chamber, which is normally used to measure the CT dose index (CTDI), some studies use smaller semiconductor photodetectors to measure the single scan dose profile (SSDP). In this case, the CT dose profiles are obtained by scanning the device through the beam using multiple rotations of the X-ray source. Some advantages of using electronic devices as radiation detectors include their high sensitivity, small physical size, no need for high voltage, and the capability of real time measurements. In this study the SSDP was obtained by using a photodiode in two ways: a detector built with only one device, and an innovative detector based on a time-multiplexing signal from an array of 31 photodiodes. Moreover, since most clinical CT examinations involve multiple scans as the patient is translated through the gantry, the novel detector was also used to obtain the multiple scan average dose (MSAD). Unprecedented results provide details of the single slice dose profile and MSAD curves, showing that such an innovative detector would be an advance in CT dosimetry and quality assurance.

Dosimetric Characterization of LiF Doped with Unusual Dopants

LiF with different dopants has been one of the most investigated materials to use as thermoluminescent dosimeter. Even so, in a previous work we observed that pellets produced with pure LiF have applicability to ionizing radiation dosimetry, showing dosimetric peaks in temperatures high enough to overcome most of fading problems. In this work we studied the thermoluminescent properties of pellets prepared with LiF and unusual dopants. As dopants were tested rare earth metals like europium, terbium, dysprosium and neodymium. The more intense TL response was showed by samples doped with Nd. Although they are bluish due to presence of the Nd, the pellets produced with LiF:Nd exhibited a TL emission two times more intense than the one in pure LiF.

Effects of ion implantation on the thermoluminescent properties of natural colourless topaz

Abstract Natural colourless topaz samples were implanted with different fluences of Cr + , Al + and Fe + ions. The thermoluminescence (TL) sensitivity to beta and gamma rays were tested and it was found that for Cr + implantations in the range of 10 14 –10 16 ions/cm 2 and for Al + in the range 10 14 –10 15 ions/cm 2 , the overall TL emissions of the samples were enhanced. The TL of the Fe + implanted samples, on the other hand, was reduced after implantation.

TL behavior of topaz-glass composite in various irradiation fields.

Abstract Topaz is a natural hard silicate mineral that has the potential to be used as a thermoluminescent dosimeter (TLD). It is difficult to manufacture chips of topaz and problematic to use its powder as TLDs. Topaz-glass composite (in the form of pellets) can be made easily and applied for radiation dosimetry. To produce pellets of topaz-glass composite in 2:1 wt (%), topaz powder was combined with commercial glass. The pellets with 6 mm diameter and 1 mm thickness were sintered in a furnace at 900°C for 1 h. The composite pellets were irradiated with x-ray and gamma photons and alpha and beta particles. The pellets yielded two peaks in the glow curve; Peak 1 at temperature range 150–160°C and Peak 2 at 250–260°C. The intensity of Peak 2 rose linearly with the increase in absorbed dose. The intensity of Peak 2 was comparable with peaks for photons and beta irradiation but relatively low for alpha exposure. The reproducibility of the intensity of Peak 2 was within 5–8%. Two months after irradiation of the pellets, the fading of the intensity of Peak 2 was found to be about 7%. The topaz-glass composite can be used effectively and efficiently for dosimetry of alpha, beta, and gamma radiation.

Aceitabilidade de um futuro banco de objetos simuladores para controle de qualidade em medicina nuclear

OBJECTIVE: The present study was aimed at determining the acceptability of a national or regional phantoms bank to be deployed in Brazil for shared use in quality control activities by nuclear medicine centers. MATERIALS AND METHODS: The authors analyzed the answers to a questionnaire applied to medical physicists and radioprotection supervisors in Brazilian nuclear medicine centers. Initially, the questionnaire was validated by professionals in the city of Aracaju, SE, which is located in the Northeast region. The present study sample was geographically distributed as follows: the Northeast region, with answers from 13 professionals of nuclear medicine centers; the North region, with 2 professionals; the South region, with 7 professionals; the Southeast region, with 43 professionals; and the Midwest region, with 2 professionals. RESULTS: According to the data analyzed, 82% of the respondents consider that the implementation of a phantoms bank would be a suitable alternative for improving nuclear medicine quality control. The interest in sharing the bank was reported by 87% of the respondents. CONCLUSION: The present study demonstrated the motivation for a shared use of a future phantoms bank.