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Corrosion and anodizing behavior of dissimilar AA5052-H32 and AA6061-T6 alloys joined by metal inert gas welding
2023 - KLUMPP, RAFAEL E.; AKBARZADEH, SAJJAD; DELAUNOIS, FABIENNE; COSTA, ISOLDA; OLIVER, MARIE-GEORGES
Enormous efforts have been made to reduce fossil fuel consumption and greenhouse gas emissions in several sectors, such as the transport and agricultural sectors. Weight reduction is an efficient way to reduce fuel consumption. In this context, Aluminum alloys are excellent choices due to their properties of lightweight and high strength. However, corrosion is a major concern when using dissimilar alloys joined by welding. This might result in galvanic corrosion. Also, thermal effects during welding might affect the microstructure and the material corrosion resistance. Consequently, the study of dissimilar materials joined by welding is of great importance. In order to decrease corrosion susceptibility, surface protection of aluminum alloys against corrosion is a core issue in these applications. In this work, the corrosion resistance of the AA5052- H32 and AA6061-T6 alloys welded by metal inert gas (MIG) welding, with or without TSA anodizing, was investigated. The corrosion resistance was evaluated by immersion tests in sodium chloride solution and monitored by electrochemical impedance spectroscopy (EIS) and as scanning vibrating electrode technique (SVET). The anodic layers formed by TSA anodizing were analyzed and characterized by Scanning Electron Microscopy with EnergyDispersive Spectroscopy (SEM-EDS) and Transmission Electron Microscopy (TEM). The results present the correlation between corrosion resistance, microstructure and surface film characteristics.
Characterization of the microstructure and corrosion behavior of electrodeposited FeMn films for bioabsorbable implants applications
2023 - GABBARDO, ALINE D.; FERREIRA, JANE Z.; COSTA, ISOLDA
Corrosion of biodegradable implants is not supposed to be avoided, but controlled to reach a target biodegradation rate [1-4]. Implants made of Fe or its alloys have been studied for this type of applications; however, they have some drawbacks as low corrosion rates for this application, accumulation of bulky corrosion products and ferromagnetic properties, which might be a problem for MRI exams [1-4]. Some improvements have been proposed in the literature, such as using electrodeposition to produce thin strut walls of Fe (or alloys) with high purity and using FeMn alloys (with high concentrations of Mn) that can form an antiferromagnetic phase with higher corrosion rates than pure Fe [1-6]. In the first part of this work, thin films of FeMn alloys were electrodeposited from sulfate electrolytes. The effects of additives and electrodeposition current density were evaluated through electrochemical techniques. The microstructure of the electrodeposited films was characterized by SEM/EDX and XRD. The surface finishing and magnetic properties were evaluated by AFM/MFM techniques. The results showed that FeMn films with a maximum concentration of 18 wt% of Mn were obtained at an applied cathodic current density of 80 mA/cm2 (close to the limiting current density) for a 1:5 ratio of Fe2+ and Mn2+ in the electrodeposition bath. These films were mainly composed of alfa-FeMn phase that still showed magnetic response on MFM analysis. The use of additives such as buffer, surfactant, and leveling resulted in a more homogenous film with improved surface finishing. In the second part of this work, the biodegradation rate of the electrodeposited film will be evaluated through immersion and electrochemical techniques in simulated body fluids.
Characterization of the corrosion behavior of Zn-Al-Mg coated steel under São Paulo acidic rain by Scanning Vibrate Electrode Technique
2023 - BOLSANELLO, MARILIA F.; ABREU, ANDREA; GUEDES, MARIA G.P.; COSTA, ISOLDA; PEREZ, JAVIER I.; ROSSI, JESUALDO L.
Smart coatings tailored to enhance the corrosion protection of steel substrates are the target of the automotive industry, as they ensure the reliability and long-term performance of coated parts. In this field, galvanized steel progresses through the last decades entail the development of more durable, reliable, and sustainable anticorrosive coatings, reducing the need for additional corrosion protection on coated components, while also lowering costs and fuel consumption in automobiles. The addition of aluminum and magnesium to the zinc bath leads to the formation of different metallurgical products in the galvanized layer, as well as more compact and stable corrosion products, increasing the service life of the steel. Also, the addition of those elements contributes to a self-repairing effect on scratches and at the cut edges, a crucial region under corrosive agents. In this study, electrochemical techniques were used to understand the corrosive process that occurs in Zn-3.5%Al3%Mg alloy coated steel (ZM), when exposed to aggressive aqueous electrolytes, and the differences in its corrosion behavior with respect to conventional galvanized steels (GI). Besides the conventional polarization analysis, samples of ZM and GI were investigated by Scanning Vibrate Electrode Technique (SVET), a local probe technique outstanding in providing information about the corrosive process in situ, on the micrometer scale. Through SVET, it is possible to visualize the corrosion progress in terms of identifying anodic and cathodic regions with estimation of the respective currents and their evolution in space and time. The tests were performed synthetic acid rain, reproducing the conditions found in the city of São Paulo. The study was complemented by Scanning Electron Microscope (SEM), Energy Dispersive X-Ray Analysis (EDX) and Glow-discharge optical emission spectroscopy (GDOES) analysis, for the identification corrosion products formed after exposure to the corrosive electrolyte. The superiority of ZM corrosion resistance over GI has been proven and attributed to the different corrosion products formed by the alloying elements added to the coating, therefore not observed in the conventional galvanized steel.
Assessment of pitting corrosion in anodized 2xxx aluminum alloys
2023 - ARAUJO, JOAO V. de S.; CHEN, JINGHUI; ZHOU, XIAORONG; COSTA, ISOLDA
This work focus on the characterization of pitting corrosion initiated in 2xxx Al alloys anodized in Tartaric Sulphuric Acid (TSA), specifically the 2024-T3 alloy substrates, and the 2198, in the T8 and T851 tempers. The results were compared to that of anodized pure Al (99.99 wt.%). The pitting corrosion resistance of the anodized samples was tested by potentiodynamic polarization in 0.1 mol L-1 NaCl solution. The tested surfaces were then characterized by optical microscopy, optical profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and image analysis by ImageJ. The polarized samples presented pits of different sizes. Some pits presented diameters of several hundred microns, with the anodic films remaining as pit covers. The pits in all anodized samples showed similar characteristics, such as, a continuous pit cover with a central hole or a pit cover detached from the substrate in some small areas. The central hole serves as a diffusion channel for dissolved species within the pits. Detachment of the pit cover occurs due to accumulation of corrosion products within the pits leading to swelling of the anodic film and its detachment from the substrate. The results showed that pit size and depth analysis measured by optical profilometry can be misleading. Depth assessment should be carried out after removal of the anodic layer followed by crosssection of the anodized sample. The pits developed under highly occluded conditions. It was also observed that in the anodized alloys, as opposed to pure Al, pits are related to the defects in the anodic films due to dissolution of micrometric intermetallic particles during the anodizing process. Pitting attack propagation occurred according to the microstructure characteristics of the tested material.
Verification of the PTOSL signal from radiation detectors using a 60Co beam and UV light from LEDs
2023 - ANTONIO, PATRICIA L.; CALDAS, LINDA V.E.
Radiation processing techniques induce physical, chemical and biological changes in the structures of materials, instruments and food to reach a certain desired benefit. For this reason, the systematic and periodic radiation dosimetry is so essential to determine the absorbed dose of radiation sources. If the absorbed dose applied to the materials does not correspond to the desired one, the effects in their structures can be adverse. Solid state dosimeters are radiation detectors that are already well established in routine procedures and described in the literature for gamma radiation dosimetry, such as 60Co, with beams employed em radiation processing. This work aims to study the response of commercial dosimeters based in their luminescence phenomenon using the optically stimulated luminescence (OSL) technique. Then, it seeks to verify the phototransfer effect presented by the dosimeters employing the phototransferred OSL technique (PTOSL), for further analysis of the possibility of applying these materials and these techniques for 60Co beam dosimetry. In this work, the OSL/PTOSL responses of LiF:Mg,Ti (TLD-100), CaF2:Dy (TLD-200), CaF2:Mn (TLD-400) and CaSO4:Dy (TLD-900) commercial dosimeters were studied in three steps: 1) OSL after irradiation; 2) OSL after irradiation + thermal treatment post-irradiation (TTPI); 3) PTOSL after irradiation + TTPI + illumination with UV of light-emitting diodes (LEDs). The irradiations were carried out with a 60Co beam from a Gamma-Cell system (383.65 Gy/h - October/2022). All the measurements were taken using the Risø reader system, model TL/OSL-DA-20, and with an illumination time of 100 s. The first phase was to irradiate the dosimeters with the following absorbed doses: 0.7 Gy (TLD-100 and -900), 20 Gy (TLD-200) and 50 Gy (TLD-900), and to measure the OSL signal. The values of the initial decay of the OSL curves were about 3x103 counts (TLD-100), 1x103 counts (TLD-200), 5.4x103 counts (TLD-400) and 9.5.102 counts (TLD-900). For the second phase, the pellets were initially irradiated with the same doses previously given and submitted to the TTPI of 280°C/15 min (TLD-100 e -900), 250°C/15 min (TLD-200) e 350°C/15 min (TLD-400); the first point of the OSL signal was observed at about 400 counts (TLD-100), 460 counts (TLD-200), 530 counts (TLD-400) and 660 counts (TLD-900). In the third phase, the dosimeters were irradiated, treated with TTPI and illuminated with UV of 265 nm/10 min (TLD-100) and 365 nm/10 min (TLD-200, -400 and -900). Comparing these last results with those from the second step, it was possible to observe PTOSL for TLD-100 and -900, because an increase in the signal intensity was observed for both materials. For TLD-200 and -400, the signals were similar for the second and third steps, but more studies are necessary for a final conclusion.
Effects of eletromagnetic radiation of different energies in blue quartz - thermoluminescence dosimetry
2023 - SILVA-CARRERA, N.B.; NILO F.C.M.; CRUZ, SOFIA P.S.; CHUBACCI, J.F.D.; WATANABE, S.
Quartz, which is the second most abundant mineral in the continental crust, is found in igneous, metamorphic and sedimentary rocks, and it belongs to the silica group, which has SiO2 as its basic composition. The quartz phase presents modifications of the α and β types, being that α-quartz is stable for temperatures below 573 °C and crystallizes trigonally, and β-quartz system is stable in between 573 °C – 870 °C and crystallizes in a hexagonal structure. Its symmetry class is 32, which means it presents structural enantiomorphism. The difference in electronegativity between oxygen and silicon creates covalent bonding (40%) as well as ionic bonding (60%). The objective of this present work is to study the dosimetric properties of blue quartz such as its reproducibility, repeatability, linearity, signal fading, and energy dependence, for its possible use as a thermoluminescent dosimeter. The natural blue quartz, purchased at the LEGEP stone store in São Paulo, was pulverized with a mortar and pestle, both made of high-hardness ceramic; the sample was then sieved to select for grains measured between 80 µm and 180 µm in diameter, and grains smaller than 80 µm were used for X-ray diffraction and X-ray fluorescence. In the powder sample, measurements were done of the thermoluminescence readings of the sample in natura, as well as of the dependence of the dose to the TL response. The blue quartz grains were sensitized using two methods: heat treatment and pre-dosing, to thus obtain the best combination of synthesis temperature, sensitization dose and activation temperature. The TL glow curve of the quartz in natura shows the TL peaks, the first being around 200 °C and the second at around 325 °C. The 325 °C peak is widely used in dating works (CANO, et al., 2015; VICHAIDIS and SAEINGJAEW, 2022; GU, et al., 2021). The selected grains were separated into packages, and irradiated with increasing doses of gamma radiation from 50 Gy to 3 kGy, and, in the emission curves obtained, it is possible to observe the TL peaks around 121 °C, 169 °C, 203 °C, 257 °C and 342 °C. Peaks below 190 °C are considered unstable in dosimetry because they disappear within a few hours, and peaks above 190 °C are considered stable peaks. For the thermal treatment method, blue quartz grains were thermally treated at 400 °C, 600 °C, 800 °C, 1000 °C and 1200 °C, followed by a rapid cooling, and then irradiated with a dose of 1 Gy. It was observed that, for the temperature of 600 °C, the emission curve presents two peaks, at 150 °C and 350 °C; for 800 °C, peaks appear around 140 °C, 204 °C and 340 °C; for the thermal treatment at 1000 °C, 2 peaks can be observed at 140 °C and 200 °C, and the peak of 340 °C is not observed; and for the treatment of 1200 °C, the TL emission curve presents a well-defined peak around 204 °C. For the pre-dosing method, eight different pre-doses between 50 Gy and 20 kGy were tested, and it was found that the blue quartz sample with a pre-dose of 500 kGy has the highest TL intensity value, and, beyond that dose, the response begins to decrease. Thus, the pre-dose of 500 Gy was chosen for testing different values of thermal activation, in which the quartz grains, after being irradiated with the pre-dose of 500 Gy, were thermally treated with temperatures of 300 °C, 400 °C , 500 °C, 550 °C, 600 °C, and 650 °C for one hour, and then irradiated with a test dose of 1 Gy. It was observed that, for 550°C, the TL intensity is maximum, and, beyond that temperature, the TL intensity begins to decrease, due to thermal deactivation occurring. Blue quartz pellets have thermoluminescent properties that make them suitable for gamma radiation dosimetry. The TL emission glow curve of the material was reproduced with the GlowFit program, showing that the curve is composed of six peaks. The linearity of the TL response was proven for up to 5 Gy, and, beyond that, it then presents a sublinear behavior. The minimum detectable dose for the pellets studied is 2.34 mGy, and the TL peak at 221 °C has less than 5 % fading, indicating that this peak can be used for dosimetry. In conclusion, blue quartz pellets can be used as passive dosimeters in gamma radiation applications, and their thermoluminescent properties have been well studied and characterized.
Study of radioluminescence from CaSO4:Eu films for real-time dosimetry
2023 - GASPARIAN, PATRICIA B.R.; MALTHEZ, ANNA L.M.C.; CAMPOS, LETICIA L.; TRINDADE, NEILO M.; OLIVEIRA, ALDO R. de; MARTINS, ROBERTO T.E.K.
Active detectors based on semiconductors and diodes are largely applied for clinical dosimetry, however they present limitations mainly related to complex electronic structure, limited spatial resolution and high cost. Several materials which exhibit thermoluminescence (TL) and optically stimulated luminescence (OSL) also present radioluminescence (RL), as Al2O3:C,Mg. In principle, RL materials can be used in real-time dosimetry as active detectors if the intensity of the RL signal can be associated with the absorbed dose. The sensitive material can be coupled to optical fibers, CCD devices, or other device to collect its light emission. The phosphor CaSO4:Eu has been studied as TL and OSL detector and literature reports good reproducibility, linear dose-response and negligible fading. Previously, CaSO4:Eu OSL films were produced and applied for two-dimensional dose mapping in radiotherapy. Considering the potential application of CaSO4:Eu films for medical applications, in this work we studied the RL emission of CaSO4:Eu films. Firstly we used a Horiba Absorbance and Fluorescence Spectrometer, model Duetta, and obtained the emission spectra of the CaSO4:Eu films, exciting with different wavelenghts and observed two emission centre groups. The first group is at 385 nm, related to Eu2+ and the second group, related to Eu3+ is at 580 nm, 600 nm and 700 nm. Secondly, to study the RL emission from the CaSO4:Eu film, we used a custom made equipment named LUMI22, which has an X-ray tube (Moxtek 50kV) powered and controlled by a standard controller (FTC-200) to irradiate the samples, and a miniature fiber optic spectrometer (Ocean Optics, FLAME-S-XR1-ES) that is used to identify the wavelength of the emitted light (range 200-1050 nm). Results showed a radioluminescent peak at 390 nm, which should be related to Eu2+. The RL sensitivity is (46.1 ± 1.3) 103 counts/Gy. The film does not need thermal or optical treatment and the radioluminescent peak is reproducible. Comparing the RL intensity after 10 consecutive irradiations with the same conditions, the maximum coeficient of variation is 2.5%. The dose response of the RL is linear (R-square 0.9959) from 0.04 to 0.3 Gy. Results show that the CaSO4:Eu film is promissing for use with the RL technique in real-time clinical dosimetry. It should be possible to evaluate dose distributions in real time using the film and a reader with several fiber optics, for example.
First dates from the Guaibituguçu archaeological site, Japaratinga, Alagoas, Brazil
2023 - MAMANI, EDWAR A.C.; ALLEN, SCOTT J.; SULLASI, HENRY S.L.; MAMANI, NILO F.C.; SANTOS, CLARA D.F.; ASFORA, VIVIANE K.; MUNITA, CASIMIRO S.; RIBEIRO, ROGÉRIO B.
The archaeological site, Guaibituguçu, located in the State of Alagoas, Brazil, is an open air site that revealed artifacts indicating an indigenous presence in context with objects of European and local non-indigenous manufacture. This study seeks to define chronological parameters for the site and to correlate the pottery chronology with the stratigraphic layers identified during excavations. Four pottery fragments were dated using Thermoluminescence techniques (TL). Each fragment was subject to mechanical treatment that removed approximately 2 mm of the artifact’s surface and the samples were ground and the grains sieved to obtain a size of >150μm. Chemical treatment to screen and select quartz grains of 75-150μm employed hydrogen peroxide, chloric acid and fluosilicate acid. The samples were used to determine the accumulated dose (Da) using multiple aliquots by way of regenerative dose method (MAR). The sediment collected associated with each fragment was sealed in a plastic container for a period of four weeks to determine the level of U, Th and K using gamma spectrometry. From these values, the external dose was inferred. Additionally, the internal dose was determined using the neutron activation technique from the U, Th and K concentrations of the artifact fragment. The sum of these two values and the cosmic radiation permitted determination of the annual dose (TD), and the calculation of sample age from the Da and TD values. All of the TL measurements were conducted using the Harshaw TLD 3500 Reader, heat rate of 5 oC/s at the Departamento de Energia Nuclear (DEN) of the Universidade Federal de Pernambuco (UFPE). A Canberra Hyperpure Germanium (GeHP) detector, coupled with and Eagle 5004 multichannel analyzer in laboratory conditions with low background radiation was used to determine the concentration of the levels of U, Th and K. The individual fragments were sent to the Instituto de Pesquisas Energéticas e Nucleares (IPEN) of the Universidade de São Paulo (USP) to determine the concentrations of U, Th and K of the samples. Analysis and discussion of results took place at the Laboratório de Estudos Arqueométricos (LEARQ) of UFPE. At this time, the age of three samples has been estimated, with accumulated doses of: 0.74±0.36 Gy; 0.79±0.12 Gy; 1.03±0.13 Gy and the TD dose levels of 0.669 mGy/year; 1.108mGy/year; 1.419 mGy/year. The resultant ages are 1148, 712, 723 and 739 years AP, considering samples S-949, S-1107 and S-1109, respectively. Sample S-5747 has not been finalized, though the ages already estimated indicate a direct relation between the age and depth where the sample was obtained. Provenance of S-949 at the deepest level and the other two at the same level may indicate two occupations. Ongoing investigations involving excavations, sampling and laboratory analysis continue with the objective of refining the chronology of Guaibituguçu.
TL and OSL characterization of CaSO4:Tb, CaSO4:Mn AND CaSO4:Mn,Tb phosphors
2023 - SILVA, ANDERSON M.B.; RODRIGUES, DANIEL S.; GUEDES, BEATRIZ D.; SILVEIRA, IURY S.; ANTONIO, PATRÍCIA L.; JUNOT, DANILO O.; CALDAS, LINDA V.E.; SOUZA, DIVANIZIA N.
The objective of this work was to investigate the luminescence properties of CaSO4:Tb, CaSO4:Mn e CaSO4:Mn,Tb synthesized by slow evaporation route. The crystalline structure, morphology, thermal and optical properties of the phosphors were characterized by X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and radioluminescence (RL). Moreover, using thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques, the dosimetric properties of the phosphors were comprehensively investigated, such as emission spectra, glow curve reproducibility, dose-response linearity, fading of the luminescent signal, OSL decay curves, correlation between TL and OSL emissions and minimum detectable dose (MDD). For dosimetric analyses the samples were irradiated with doses of between 169 mGy and 10 Gy. TL emission spectra confirmed the presence of Tb3+ and Mn2+ ions in crystalline matrices. The samples showed a typical exponential OSL decay curve with the predominance of a fast decay component, indicating that the traps have a high photoionization cross-section for blue LEDs, and a MDD on the order of mGy. The luminescent signals showed to be linear and reproducible in the studied dose range. The trapping centers located between 0.63 eV and 1.07 eV were revealed. The high TL sensitivity of phosphors was proven when comparing with commercially available dosimeters. It was also observed that co-doping with Mn and Tb contributed to a reduction in fading compared to CaSO4:Mn and CaSO4:Tb.
Computational and experimental analyses on the origin of TL and OSL signals in undoped and doped compounds
2023 - VALENÇA, JOAO; TROMBINI, HENRIQUE; OTSUKA, ANDRE; SILVEIRA, IURY S.; CALDAS, LINDA V.E.; SOUZA, ANTONIO O. de; SOUZA, ADELMO S.; SANTOS, JORGE L.O.; COELHO, VINICIUS; MATOS, HEVESON L.L.
The main objective of this work is to present the current knowledge concerning the origin of the luminescent signal generated through Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) techniques in well-known compounds. The discussion about this mechanism involves experimental analysis, atomistic simulation, and literature review. Materials such as undoped or doped magnesium tetraborate (MgB4O7) were examined as examples. The atomistic simulation was carried out using GULP, a well-established tool that enables, among others, the analysis of energy formation of various point defects. The experimental measurements were conducted using the Riso reader on materials that were produced and characterized. Combining different methodologies, it became feasible to ascertain the most likely point defects in each studied compound. The outcomes obtained from the study of undoped MgB4O7 enabled the identification of the likely defects responsible for the emitted signal in this material. We also developed a proposal to explain the formation of the MgO anti-Schottky defect, which presented the lowest energy solution (eV/defect) among the analysed defects. In the case of Li-doped MgB4O7, a hypothesis was postulated to elucidate the suppression in the signal caused by the presence of lithium. Furthermore, computational analysis was conducted on Ce-doped and Ce-doped/Li-codoped MgB4O7, which has garnered significant attention due to its potential applications as TLD and, more notably, OSLD. In this instance, experimental analysis and literature review revealed compelling evidence of a complicated correlation between the dopant concentrations and the resulting signals, which require further investigation in future studies. This type of information is highly significant in the present era when better comprehension of the origin of the signal could lead to an enhanced capability to design new dosimeters and gain deeper insights into the behavior of currently used materials.
Phototransferred thermoluminescence in commercial dosimeters after exposure to beta radiation
2023 - ANTONIO, PATRICIA L.; CALDAS, LINDA V.E.
Radiation dosimetry allows the analysis of the energy deposited in a material to evaluate the effect caused on this material; it can be done using different radiation detectors, and there are several dosimetric materials that can be employed, according to the radiation kind and the purpose of its application. A material can only be considered a radiation dosimeter if it presents certain conditions; for dosimeters that present luminescent response, it is necessary to present specific characteristics in this luminescence signal. However, there are ways to study the signal to allow the response obtained to provide these characteristics, for example, studying the phenomenon of phototransfer of the luminescent signal of a material. The main objective of this work was to analyze the occurrence of phototransfer on the thermoluminescence (TL) of different commercial dosimeters, the phenomenon of the phototransferred TL (PTTL). For this, the TL and PTTL responses of LiF:Mg,Ti (TLD-100), CaF2:Dy (TLD-200), CaF2:Mn (TLD-400) and CaSO4:Dy (TLD-900) dosimeters were investigated using the 90Sr+90Y source of the TL/OSL reader system Risø. During the TL/PTTL measurements, performed with the same reader, the maximum temperatures were 350°C (TLD-200), 400°C (TLD-100 e -900) e 450°C (TLD-400), and the heating rate was kept constant at 10°C/s. The first step was to verify the TL response of the materials, by means of the TL emission curves after irradiation (with absorbed doses of 0.7 Gy for TLD-100 and TLD-900, 20 Gy for TLD-200 and 50 Gy for TLD-400). The main peaks were observed at the temperatures of 252°C for TLD-100, 312°C for TLD-200, 398°C for TLD-400 e 226°C for TLD-900. The second step was to analyze the TL response after irradiation and a thermal treatment post-irradiation (TTPI) of 280°C/15 min for TLD-100 e TLD-900, 300°C/15 min for TLD-200 and 400°C/15 min for TLD-400; the highest TL emission occurred at 362°C (TLD-100), 139°C (TLD-200), 398°C (TLD-400) and 397°C (TLD-900). The third step was the verification of the PTTL signal, obtained after irradiation, TTPI and illumination (with UV leds) of the materials at the conditions of 265 nm/5 min for TLD-100 and 365 nm/5 min for TLD-200, TLD-400 e TLD-900. For TLD-100, a PTTL signal was verified, because two new peaks emerged at 133°C and 261°C; for TLD-200 and TLD-400 no PTTL signal was observed; for TLD-900 it was possible to obtain a PTTL response once a peak appeared at 197°C, which did not exist after irradiation and TTPI (second step). In order to continue studying the PTTL signal, this response was verified varying the illumination time for the four materials between 2.5 min and 25 min. The PTTL response maximum was observed for 15 min illumination for all the materials. The PTTL was also studied in function of the wavelength for 265 nm, 310 nm, 365 nm, 400 nm e 420 nm; the results showed that the most intense signal occurred at 265 nm for TLD-100, -400 and -900, and 365 nm for TLD-200.
Evaluation of TL and OSL responses of recycled crab shell biowaste for radiation dosimetry
2023 - JUNOT, DANILO O.; SILVA, ANDERSON M.B.; REZENDE, YARA R.R.S.; SOUZA, DIVANIZIA N.; REZENDE, MARCOS V.S.; CALDAS, LINDA V.E.
The aim of this work was to evaluate the applicability of crab shell biowaste composites as thermoluminescent (TL) and optically stimulated luminescent (OSL) detectors, since recent researchers have found it to be a valuable intrinsic luminescent material. The waste of crabs shells (Ucides cordatus) species was taken from a bar located at Atalaia beach in Aracaju city, Sergipe State, Brazil, and calcined at 800 °C for 2 h. The calcined crab shell powder was mixed with Teflon (2:1 mass ratio) and molded in pellets of 6 mm diameter and 1 mm thickness. The pellets were sintered at 400 ºC for 1 h. The luminescent and dosimetric characterization of the crab shell composites were performed using a TL/OSL Risø Reader, model DA-20. The crab shell composites showed TL signals between 100°C and 400°C, with an intense peak around 155°C and a less intense peak around 350°C. The first peak, although at a relative low temperature, can be used as a dosimetric peak, due to its high intensity and acceptable fading (12% after 7 days). The OSL signal of the samples was very intense and with a very fast decay, which means that the luminescent centers are easily optically stimulated by the reader blue LEDs. The emission spectra of the samples showed a broad emission from 300 nm to 400 nm. All samples produced showed variation coefficients for homogeneity and reproducibility below 9.5%, in addition to a linear response in the dose range used (80 mGy to 1 Gy) and minimum detectable doses of the order of miligrays. Evaluating the dosimetric applicability, the crab shell composites presented potential application as TL/OSL detectors in processes that employ ionizing radiation such as beta particles, X and gamma rays.
Development of CaSO4:TR,Li (TR = Tm, Eu, Tb) composites for beta radiation dosimetry by means of luminescent techniques
2023 - JUNOT, DANILO O.; GALEANO, DIEGO C.; SOUZA, DIVANIZIA N.; CALDAS, LINDA V.E.
The study of new dosimetric materials for investigations in ionizing radiation dosimetry is extremely important to provide sensitive and low-cost detectors. Thus, this work proposed the development of CaSO4:Tm,Li, CaSO4:Tb,Li and CaSO4:Eu,Li composites for application in beta radiation dosimetry, using luminescent techniques such as thermoluminescence (TL) and optically stimulated luminescence (OSL). The CaSO4 crystals were produced by the adapted slow evaporation route and characterized using X-ray diffraction (XRD), radioluminescence, TL and OSL techniques. XRD analyses showed that the doped CaSO4 samples presented a single phase, with orthorhombic symmetry. The CaSO4:Eu,Li composites showed TL signals between 100°C and 200°C, with peaks around 145°C and 180°C. The CaSO4:Tb,Li and CaSO4:Tm,Li composites showed TL signals between 100 ºC and 350 ºC, with peaks around 165 ºC and 275 °C. All samples were irradiated with a 90Sr/90Y source from the TL/OSL Risø reader. For the CaSO4:Tb and CaSO4:Tm samples, the addition of lithium as co-dopant resulted into a significant increase (2x) in the total TL signal of the samples. The CaSO4:Tm,Li samples presented a very intense OSL signal, about 80x greater than the signal of the other samples produced. This allows the applicability of TL/OSL detectors even more sensitives. The OSL decay of the CaSO4:Eu,Li and CaSO4:Tb,Li samples is dominated by a fast decay while the OSL signal of CaSO4:Tm,Li composites decays slowly and remains stored for a long time. The TL emission spectra of the samples showed typical emissions of Eu2+ ions (280 nm), Eu3+ (614 nm), Tb3+ (544 nm) and Tm3+ (455 nm). As no emission corresponding to lithium was identified in the emission spectra, it can be assumed that lithium acts as a capture center and transfers its energy to the nearby TR3+, which increases the emission intensity. All the samples produced showed linearity in the dose range used, good reproducibility, with variations below 10%, and minimum detectable doses of the order of micrograys. The evaluated dosimetric characteristics denote that the developed composites have potential application as TL/OSL dosimeters.
Calibration of 90Sr + 90Y planar sources using thermoluminescent samples, a PMMA phantom and Monte Carlo simulation
2023 - LITVAC, DANIEL; CLDAS, LINDA V.E.
In certain regions of Brazil, 90Sr/90Y clinical applicators continue to be employed for dermatological and ophthalmic treatments, even though newer technologies, such as the 106Ru/106Rh Eye Applicator, are available worldwide. The use of these older applicators persists due to their lower cost and greater ease of use. However, it is crucial to calibrate and periodically recalibrate these applicators to ensure that the absorbed dose rates are accurate, and that the quality of clinical treatments is maintained. This study examines the thermoluminescent response of µLiF pellets to evaluate their reproducibility, linearity of response, and dose-response curves. Two radiation systems were used to characterize the dosimetric material. The first system is part of a Risö reader system (Risö TL/OSL-DA-200 model) with a 90Sr/90Y source, operating at a dose rate of 0.1 Gy/s (2010). The second system is a 90Sr/90Y source from the beta secondary standard system (BSS2) with a dose rate of 123.32 µGy/s (2005), from Amersham Buchler, calibrated in the German Primary Standard Laboratory, Physikalisch-Technische Bundesanstalt (PTB). The BSS2 system presents its calibration certificate in air and in ICRU 4-element tissue (k=2). The uncertainties in the thermoluminescent measurements for some measurement cycles of µLiF samples, irradiated with 1 Gy of beta radiation, Risö system, remained up to 5%. Linearity and dose-response curves were obtained over a dose range from 0.3 to 1 Gy using the BSS2 system. The R2 values for the µLiF samples ranged from 0.9974 to 0.9998. The dose rates for three clinical applicators were determined using µLiF pellets, a PMMA phantom, and the Monte Carlo method. This project followed the guidelines outlined in ISO 21439 (2009), which recommends the use of small detectors like µLiF for this type of calibration. Monte Carlo simulation was used to determine correction factors between absorbed dose in air, water, and PMMA, ensuring the use of PMMA in clinical applicator calibration. The PMMA has a cubic shape, a slot to keep the µLiF at a one-millimeter depth, and dimensions that ensure total absorption of beta radiation without interaction with air. The percentage differences between the µLiF calibration and the manufacturer calibration values were equal to or greater than 10%. The main reasons for these results are discussed in this work.
Characterization of mammography digital detectors
2023 - PEREZ, ALESSANDRA M.M.M.; LOPES, LAURA A.S.; CARON, RENATO F.; OLIVEIRA, BRUNO B.; CALDAS, LINDA V.E.; POLETTI, MARTIN E.
Recent measurements introduced in quality control protocols indicate large variations in the evaluated parameters, pointing out as its main cause the different detectors used. The objective of this work was to characterize, in terms of signal transfer property (STP) and noise component analysis (NCA), five mammography digital detectors at different dose levels for a variety of beam qualities. A Carestream EHR-M3 CR detector and Planmed Clarity, Siemens Opdima, GE Pristina and GE Crystal Nova DR detectors were characterized in terms of STP and NCA, as a function of detector air Kerma (DAK) at the X-ray detector input plane, in the range of 4 to 1000 µGy. A PTW Unidos E with PTW Freiburg ionization chamber was used to measure DAK. Attenuated beam qualities (obtained by adding 2 mm Al to the corresponding beam qualities) used were 28 kV with anode/filter combination Mo/Mo for the EHR-M3, Opdima and Pristina detectors; 28 kV with W/Rh for the Crystal Nova; 28 kV with W/Ag for the EHR-M3 and Clarity detectors; and 34 kV with Rh/Ag for the Pristina. STP measures the relationship between the input (DAK) and the output (pixel value) detector signals. NCA gives the fraction of total noise of each of its components and was calculated from the variance in mean pixel value. Both parameters were determined under stipulated (geometric and irradiation) conditions given in EUREF quality control protocol (2013). CR detector showed a logarithmic response and DR detectors showed linear response in the tested dose range (R² > 0.999). Response function was also influenced by the kVp and anode/filter combination used. W/Ag and Rh/Ag beams presented higher slope and intercept for EHR-M3 and Pristina, respectively. NCA showed that Opdima and EHR-M3 detectors are quantum limited below 270 and 900 µGy, respectively. For higher dose values, structure noise is the dominant noise source. For the Opdima detector, structure noise is related to the presence of wide range inhomogeneities in the data, while for CR detectors, it is related to the phosphor grain size. All other detectors are quantum limited in the dose range evaluated. The findings show that the signal transfer and noise characteristics are influenced by the properties of the detection system. Moreover, STP was influenced by the beam quality.
Development of Ce3+-doped magnesium borate glass-ceramic for optically stimulated luminescence dosimetry
2023 - VASCONCELOS, DANIEL A.A. de; SOUZA, MAURICIO L.; ZANOTTO, EDGAR D.; CALDAS, LINDA V.E.
Among several new optically stimulated luminescence (OSL) materials that have been investigated, magnesium borate has been attracting attention as a host material for dosimetry-based techniques, such as OSL and thermoluminescence (TL), for reasons such as effective atomic number similar to water and tissues, and the possibility to produce a neutron sensitive material, by controlling the host content of 10B isotope. More specifically, Ce3+-doped MgB4O7 has also been proposed as a potential OSL material for 2D dosimetry, because of its fast luminescence. Although the literature on sintered MgB4O7:Ce is abundant, the objective of this work is to produce this material (Ce3+-doped magnesium borate) in the form of glass-ceramic, which has many advantages, such as good formability in complex shapes, low cost, fast mass production and denser than conventional powder sintered materials, and might lead to dosimetric improvement. The Ce3+-doped magnesium borate was produced following the composition of 55B2O3 – 45MgO – 0.3 CeO2 (mol), which was normalized thereafter to obtain 100%. After being weighted and mixed uniformly, the mixture was melted at ~1250 °C for 1 h, and the final glass was obtained by splat cooling between two steel plates. Both the powder of ~60 µm and pellets of 5x5 mm2 and 0.6 mm width were obtained for further investigation, which began with a structural analysis of the material. DSC measurements were performed to define the thermal treatments for crystallization. Five temperatures were chosen symmetrically between the glass transition range, 630 °C, and the DSC crystallization peak temperature of 814 °C. Both monoliths and powder were treated at these temperatures for 3 h, and XRD measurements were carried on the crystallized powder to verify if the samples underwent crystallization or not. The samples treated at the first two temperatures, 630 °C and 676 °C remained glassy, whereas the samples treated at 722 °C, 768 °C and 814 °C showed XRD peaks with the same predominant pattern as the reference material for triclinic Mg2BO5 (COD 96-200-3244). A Risø TL/OSL reader, with an integrated 90Sr/90Y beta source (0.08 Gy/s, in 2023) was used for both reading and irradiating the samples. The monoliths treated under all conditions underwent a preliminary dosimetric characterization; first, after being irradiated with 0.8 Gy a TL glow curve was obtained to verify the peak positions and their thermal stability. Both 630 °C and 676 °C treated samples showed one wide peak at around 80 °C, which is related to shallow electron traps, while samples treated with 722 °C, 768 °C and 814 °C showed two main peaks, one at 100 °C, and the second, 220 °C, due to shallow and deep electron traps, respectively. Accounting for the fading of the shallow electron traps, a high reproducibility, from 0.4% to 4.2% standard deviation, was observed in the OSL measurements. The full dosimetric characterization is expected to be completed before the conference.
Calibration of 90Sr /90Y Ophthalmic Brachytherapy Planar Sources Using Thermoluminescent Samples, a PMMA Phantom and Monte Carlo Simulation
2023 - LITVAC, DANIEL; CALDAS, LINDA
In some parts of Brazil, 90Sr/90Y clinical applicators are still used for dermatological and ophthalmic treatments, despite the availability of new technologies worldwide and the use of Ru-106/Rh-106 Eye Applicator. This is because they are less expensive and easier to use. Calibration and periodic recalibration of these applicators to verify the absorbed dose rate are essential to ensure accuracy in clinical treatments. In this study, the thermoluminescent response of LiF pellets was evaluated to determine the reproducibility, linearity of response, and dose-response curves. Dose rates for some clinical applicators were determined using the LiF pellets, a PMMA phantom and the Monte Carlo method, following a project based on ISO 21439 (2009). This standard recommends the use of small detectors such as LiF for this type of calibration.
Brazilian aeolian sediments dating using tl, osl and esr
2023 - CARMO, LUCAS S. do; WATANABE, SHIGUEO; DEWITT, REGINA
In this work, a dunefield known as Dama Branca (Brazil) has been dated using the following techniques: Optically Stimulated Luminescence (OSL), Thermoluminescence (TL) and Electronic Spin Resonance (ESR). They are part of what is called “trapped charge dating technique”. Sediments have been collected from several points to study age distribution throughout Dama Branca. These ages are related to events of sediment transportation and stabilization. For Dama Branca specifically, variables related to weather such as rainfall and wind power are suspected to be responsible for its formation. OSL results were obtained applying the SAR protocol. TL and ESR results were obtained using the Multiple Aliquot Additive Dose protocol (MAAD). With respect to ESR measurements, the Ti-Li center was chosen for dating since it can be completely bleached by sun light exposure , which makes it suitable for aeolian sediment dating. The Ti-Li center is strongly dependent upon preheat, its stability has been assessed and a preheat temperature of 180 °C was selected. OSL ages are within 0.05 kyears and 2.05 x kyears. TL ages agree with OSL ages for samples collected from the dune base, however there are discrepancies between OSL and TL ages for the DBM2BASE sample, suggesting that it underwent a quicker burial process. ESR results are satisfactory for two samples, 2DB10 and 2DB11 (they follow OSL and TL results). The ages were compared to a simplified morphological study. In recent works about the weather in the Cabo Frio region it has been seen that the studied areas were formed under influence of arid conditions and cold water, variables that control sediment transportation in the region. Keywords (max. 5): TL, ESR, OSL, quartz, sediments dating.
Thermoluminescence (TL) properties of yellow beryl pellets
2023 - CARMO, LUCAS S. do; CARRERA, BETZABEL N.S.; WATANABE, SHIGUEO; CHUBACI, JOSE F.D.
Beryl is a silicate with chemical formula Be3Al2(SiO3)6 commonly found in Brazil. It has a few colored variations used as jewelry, like Aquamarine (blueish), Emerald (green) and Heliodor (yellow). In this work, Heliodor pellets of 5 mm diameter and 1 mm thickness have been produced and investigated using thermoluminescence (TL) to evaluate its potential for use as gamma ray’s dosimeter. The results show that the pellets exhibited a prominent TL peak at 205 °C that grows linearly with dose when irradiated from 1 Gy to 1000 Gy. Deconvolution of the TL peaks was carried out using CGCD (Computerized Glow Curve Deconvolution) method. The peak positions were determined using the Tm/Tstop method described in McKeever (1985). Samples were stored in dark room at room temperature for 21 days to evaluate the fading of the TL signal, the main TL peak at 205 °C did not show any decrease in intensity.
Microstructure and electrical conductivity of sol-gel synthesized and spark plasma sintered doped-lanthanum gallate
2023 - MUCCILLO, E.N.S.; REIS, S.L.; GONIN, C.F.N.; BERTON, M.A.C.; MUCCILLO, R.
Perovskite ceramics consisting of lanthanum gallate with partial substitutions for strontium and magnesium are candidates as solid electrolyte for application in solid oxide fuel cells operating at intermediate temperatures (~550 to ~750ºC). The main concern related to the application of this perovskite solid electrolyte is impurity phases, usually detected even in chemically synthesized powders. The La0.9Sr0.1Ga0.8Mg0.2O3-d (LSGM) composition display relatively low contents of impurity phases. In this work, the LSGM composition was synthesized by the sol-gel method and consolidated by spark plasma sintering to optimize the microstructure and electrical properties of this solid electrolyte. Chemically synthesized powders were consolidated in the 1100 to 1250ºC for 5 min. Sintered specimens with relative densities higher than 98% were obtained. Rietveld analysis of X-ray diffraction data revealed no detectable impurity phases. The microstructure evolution exhibited submicron sized grains with mixed fracture mode. High values of the electrical conductivity were obtained for all specimens.

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