R. Bernal

Thermally and optically stimulated luminescence of new ZnO nanophosphors exposed to beta particle irradiation

In this work, we report on the thermoluminescence (TL) and the optically stimulated luminescence (OSL) of ZnO nanophosphors obtained by thermal annealing of ZnS powders synthesized by precipitation in a chemical bath deposition reaction. To obtain nanocrystalline ZnO, ZnS pellet-shaped samples were subjected to a sintering process at 700 °C during 24 h exposed to air at atmospheric pressure. Some samples were exposed to beta particles in the 0.15–10.15 kGy dose range and the integrated TL as a function of dose increased with dose level, with no saturation indication for the tested dose levels. Computerized glow-curve deconvolution of the experimental glow curves in individual peaks revealed a second-order kinetics. In order to test the OSL response, samples were irradiated with beta particles with doses up to 600 Gy, and an increasing intensity as dose increased was observed. We conclude that the new ZnO phosphors under investigation are good candidates to be used as dosimetric materials.

Biocompatibility of crystalline opal nanoparticles

BackgroundSilica nanoparticles are being developed as a host of biomedical and biotechnological applications. For this reason, there are more studies about biocompatibility of silica with amorphous and crystalline structure. Except hydrated silica (opal), despite is presents directly and indirectly in humans. Two sizes of crystalline opal nanoparticles were investigated in this work under criteria of toxicology.MethodsIn particular, cytotoxic and genotoxic effects caused by opal nanoparticles (80 and 120 nm) were evaluated in cultured mouse cells via a set of bioassays, methylthiazolyldiphenyl-tetrazolium-bromide (MTT) and 5-bromo-2′-deoxyuridine (BrdU).Results3T3-NIH cells were incubated for 24 and 72 h in contact with nanocrystalline opal particles, not presented significant statistically difference in the results of cytotoxicity. Genotoxicity tests of crystalline opal nanoparticles were performed by the BrdU assay on the same cultured cells for 24 h incubation. The reduction of BrdU-incorporated cells indicates that nanocrystalline opal exposure did not caused unrepairable damage DNA.ConclusionsThere is no relationship between that particles size and MTT reduction, as well as BrdU incorporation, such that the opal particles did not induce cytotoxic effect and genotoxicity in cultured mouse cells.

Thermally stimulated luminescence of Mg-doped ZnO Nanophosphors

Nanosized ZnO:Mg phosphors were synthesized through a controlled chemical reaction. X-ray diffraction patterns confirmed that Mg entered in a substitutive way in Zn sites. To investigate their thermoluminescence (TL) properties, some samples were exposed to beta-particle irradiation. The results reported here show that Mg doping improves ZnO TL features that are important for TL dosimetry applications, such as the shape of the glow curve, the temperature at which the maximum TL intensity is observed, and the TL fading and reproducibility. No saturation clues of the TL response as a function of the dose is observed for doses below 1600 Gy.

Thermoluminescence of novel zinc oxide nanophosphors obtained by glycine-based solution combustion synthesis

High-dose thermoluminescence dosimetry properties of novel zinc oxide nanophosphors synthesized by a solution combustion method in a glycine-nitrate process are presented for the very first time in this work. Sintered particles with sizes ranging between ∼500 nm and ∼2 µm were obtained by annealing the synthesized ZnO at 900°C during 2 h in air. X-ray diffraction patterns indicate the presence of the ZnO hexagonal phase, without any remaining nitrate peaks observed. Thermoluminescence glow curves of ZnO obtained after being exposed to beta radiation consists of two maxima: one located at ∼149°C and another at ∼308°C, the latter being the dosimetric component of the curve. The integrated TL fading displays an asymptotic behavior for times longer than 16 h between irradiation and the corresponding TL readout, as well as a linear behaviour of the dose response without saturation in the studied dose interval (from 12.5 up to 400 Gy). Such features place synthesized ZnO as a promising material for high-dose radiation dosimetry applications.

Thermoluminescence of Tequila-based nanodiamond

Nanodiamond thin films were deposited onto Si (100) substrates using Tequila as precursor by pulsed-liquid injection chemical vapour deposition at 850 degrees C. Some samples were exposed to beta particle irradiation in the dose range from 100 to 1600 Gy, and it was found that the thermoluminescence (TL) response is a linear function of dose. The glow curve displays two maxima centred at 170 and 350 degrees C, which does not shift when dose changes, indicating that first-order kinetics processes are involved. From the results, it is concluded that the new nanodiamond films are promising high-dose TL dosimeters.

High dosage thermoluminescence diamond dosimeters

Diamond thin films have been irradiated with high doses (up to 12.8 kGy) of 90Sr beta particles. The diamond thin films have been synthesized from commercial Tequila as a precursor using Pulsed Liquid Injection by the Chemical Vapor Deposition (PLICVD) technique reported recently. Thermoluminescence (TL) phenomena at these doses exhibit peak curve shift to higher temperatures (from 370 to 440 K) in the glow curve and the integrated TL curve show a linear behavior. Therefore, it has been considered that diamond thin films could be used as high doses dosimeters.

Synthesis and Thermoluminescence of New ZnO Phosphors

In this work, the synthesis and thermoluminescence properties of new ZnO phosphors obtained by a chemical method are reported. Some samples were exposed to beta particle irradiation for doses ranging from 10.0 up to 6,400 Gy, and it was found that the thermoluminescence response as a function of dose is linear for doses below 200 Gy, and sublinear with no saturation clouds for greater doses. A broad shape glow curve with maximum located above 230 °C, that shifts to lower temperatures as dose increases, indicating that second order kinetics thermoluminescence processes are involved. The lower detection limit was estimated to be 13 Gy. We conclude that the phosphors under study are promising to develop dosimeters for high dose radiation dosimetry.

Thermoluminescence of NaCl:Cu sintered phosphors exposed to beta irradiation

NaCl:Cu pellet-shaped phosphors were synthesized through a sintering process. Some samples were exposed to beta irradiation in order to investigate their thermoluminescence properties and capabilities to be used in detecting and measuring ionizing radiation. The glow curves reveal at least four thermoluminescence peaks below 250°C, and a main one above 300°C when a 5°C/s heating rate is used. The lowest temperature peak vanishes in less than 3 min after irradiation, giving rise to an intense afterglow luminescence, potentially useful for in situ non-thermoluminescence dosimetry, and the next remains for about 3 h, but the high temperature one exhibits no important changes after that time. The thermoluminescence intensity increased as the radiation dose increased in the 0.417–25.0 Gy dose range. Because the position and the remarkable stability of the higher temperature peak, besides the strong afterglow produced by the fast decaying of the lower temperature peak, it is concluded that these phosphors are very suitable candidates to be used in both thermoluminescence and non thermoluminescence dosimetry of ionizing radiation, having advantages over monocrystals of similar composition. The synthesis route here followed can be reproduced in standard college laboratories, and thermoluminescence be measured in home-made systems, allowing design practices for interdisciplinary physics, chemistry electronics, and materials science students.

Fabrication and characterization of new LiF:Eu3+ sintered phosphors exposed to beta particles

Pellet-shaped LiF:Eu3+ phosphors were synthesized by sintering. To improve their thermolumine-scence characteristics, different growth conditions were used. Thermal annealing at 750 °C during 5 h under air atmosphere provided the samples with highest sensitivity. Characteristic glow curves exhibit an absolute maximum centered at 203 °C and another less intense peak between 250 and 300 °C. The first peak has a position very suitable for dosimetry applications. Beta-irradiated samples displayed a thermoluminescence response that increases as the radiation dose increased in the 0.16–42.0 Gy range. A fast fading of<20% occurs in the first 10 s after irradiation, followed by a remarkable stability at room temperature. Computerized glow curve deconvolution of experimental data obtained applying the McKeever method to resolve the individual peaks revealed that the glow curves fit to nine individual peaks. Activation energies were computed by using the initial rise method.

Thermoluminescence characterization of LiMgF3:DyF3 phosphors exposed to beta radiation

LiMgF3:DyF3 phosphors were obtained as polycrystalline solids from the melting of component salts, with two DyF3 concentrations, 2.02% mol and 4.04% mol. In order to guarantee the homogeneity of the composition, the samples were crushed and the resulting powder was pressed to form pellet-shaped phosphors, some of which were sintered at 700 °C for 5 h, under atmospheric air. Thermoluminescence measurements of beta irradiated samples show that these phosphors exhibit adequate properties to be considered for development of thermoluminescence dosimeters. Integrated thermoluminescence as a function of dose displays a linear dependence with dose for doses below 20.0 Gy.