RESUMO
BACKGROUND: Fiber optic dosimetry (FOD) has emerged as a useful technique that can be used in those cases when intracavitary, real time, high spatial resolution dose assessment is required. Among the several factors characterizing a dosimeter, angular response of FOD probes has to be assessed in order to consider possible clinical application. PURPOSE: The objective of this study was to characterize the angular response of a FOD probe based on a cylindrical shaped YVO4 :Eu3+ scintillator under irradiation with a 6 MV photon beam generated by a linear accelerator (LINAC). METHODS: A FOD probe was irradiated inside a plastic phantom using a 6 MV LINAC photon beam at different azimuthal angles (0° to 360°, 15° steps). Scintillation output was measured with a photomultiplier tube. Similar measurements were performed with a second FOD probe having an optical filter interposed between the scintillator and the fiber. Monte Carlo simulations using PENELOPE were carried out in order to interpret the observed results. RESULTS: The FOD output was symmetrical with respect to the scintillator axis. For the unfiltered probe, the signal was maximum at rear incidence (0°) and steadily decreased down to its minimum value at frontal incidence (180°) having a signal ratio of 37%. The output of the filtered probe showed a plateau from 15° up to 115°. The signal was maximum at 60° and minimum at 180° having a signal ratio of 16%. Monte Carlo simulations predicted symmetry of the deposited dose about 0° and 90°, which contrasts with experimental findings. CONCLUSIONS: Photoluminescence (PL) of the scintillator induced by the Cherenkov light increases the angular dependence. Radiation attenuation inside the scintillator and partial light collection of the scintillation yield by the optical fiber (OF) are responsible for asymmetrical response. Results from this study should be considered in order to minimize angular dependence in FOD.
Assuntos
Radiometria , Contagem de Cintilação , Contagem de Cintilação/métodos , Radiometria/métodos , Tecnologia de Fibra Óptica , Fibras Ópticas , Aceleradores de PartículasRESUMO
This paper presents a fast and automatic flow-based method to extract 131I from biological samples and hospital waste, previous to liquid scintillation detection. 131I is a radionuclide extensively used in Nuclear Medicine due to their beta and gamma disintegrations, whereby hospitals have to manage the associated waste generation. The automatic developed system is based on Lab-On-Valve (LOV) flow-technique exploiting Cl-resin (135â¯mg per extraction). This methodology allows performing sample extractions and measurements on the same day, since the extraction frequency takes 1.4-4 h-1, depending on the analysed sample volume, plus up to 2â¯h of measurement for each vial. 131I is retained as iodine ion and eluted with sodium sulphide 0.2â¯molâ¯L-1. The maximum sample volume that can be preconcentrated is 20â¯mL, reaching an extraction efficiency of 85⯱â¯5%. The minimum detectable activity (MDA) is 0.05 Bq, showing a precision of 7% RSD (nâ¯=â¯5). Both, biological samples (urine and saliva) and hospital waste samples can be satisfactorily analysed by the proposed system, obtaining recoveries between 90 and 110%. The developed method is then suitable to implement in hospitals, improving the surveillance of the 131I environmental release.
Assuntos
Análise de Injeção de Fluxo/métodos , Hospitais/provisão & distribuição , Radioisótopos do Iodo/análise , Resíduos de Serviços de Saúde/análise , Contagem de Cintilação/métodos , Humanos , Radioisótopos do Iodo/urina , Saliva/químicaRESUMO
We present the performance evaluation of a large-area detector module based on the ArrayC-60035-64P, an 8×8 array of tileable, 7.2mm pitch, silicon photomultipliers (SiPM) by SensL, covering a total area of 57.4mm×57.4mm. We characterized the ArrayC-60035-64P, operating at room temperature, using LYSO pixelated crystal arrays of different pitch sizes (1.075, 1.430, 1.683, 2.080 and 2.280mm) to determine the resolvable crystal size. After an optimization process, a 7mm thick coupling light guide was used for all crystal pitches. To identify the interaction position a 16-channel (8 columns, 8 rows) symmetric charge division (SCD) readout board together with a center-of-gravity algorithm was used. Based on this, we assembled the detector modules using a 40×40 LYSO, 1.43mm pitch array, covering the total detector area. Calibration was performed using a 137Cs source resulting in excellent crystal maps with minor geometric distortion, a mean 4.1 peak-to-valley ratio and 9.6% mean energy resolution for 662keV photons in the central region. The resolvability index was calculated in the x and y directions with values under 0.42 in all cases. We show that these large area SiPM arrays, combined with a 16-channel SCD readout board, can offer high spatial resolution, without processing a big number of signals, attaining excellent energy resolution and detector uniformity.
Assuntos
Tomografia por Emissão de Pósitrons/instrumentação , Calibragem , Radioisótopos de Césio , Desenho de Equipamento , Radioisótopos de Flúor , Mamografia/instrumentação , Contagem de Cintilação/instrumentação , SilícioRESUMO
Fiberoptic dosimetry (FOD) is an experimental technique suitable for in-vivo, real time dosimetry in radiotherapy treatments. FOD relies on using a small scintillator coupled to one end of a long optical fiber. The scintillator is placed at the point where the dose rate is to be determined whereas a light detector at the other end of the fiber measures the intensity of the radioluminescence emitted by the scintillator. One of the problems hampering the straightforward application of this technique in clinics is the presence of Cherenkov radiation generated in the fiber by the ionizing radiation, which adds to the scintillating light and introduces a bias in the dose measurement. Since Cherenkov radiation is more important in short wavelength range of the visible spectrum, using red-emitting scintillators as FOD detectors permits to reduce the Cherenkov contribution by using optical filters. In this work, the performance of red-emitting tellurium-doped zinc selenide crystal as FOD detector is evaluated and compared to the response of an ion-chamber.
Assuntos
Fibras Ópticas , Radiometria/métodos , Compostos de Selênio , Telúrio , Compostos de Zinco , Sistemas Computacionais , Tecnologia de Fibra Óptica , Humanos , Medições Luminescentes/métodos , Neoplasias/radioterapia , Radiocirurgia , Dosagem Radioterapêutica , Contagem de Cintilação/métodosRESUMO
It is proposed a method for the determination of (226)Ra in offshore platform liquid effluent samples (produced water). The method is based on a two-phase liquid scintillation counting system and allows for the direct and simple determination of (226)Ra content. Samples with high barium content may also have high (226)Ra concentration. Therefore, the sample volume is based on the barium concentration and ranges from 10 mL to 100 mL. Our new method was tested using multiple real samples and was compared with the BaSO4 precipitation method. The results based on the LSC were 30% higher than the precipitation method, which is attributed to the self-absorption of alpha particles in the BaSO4 precipitate. The determination of both (226)Ra and (228)Ra in the liquid effluent of offshore oil platforms is mandatory in Brazil. Thus, a second method of accurately assessing (228)Ra content remains necessary.
Assuntos
Campos de Petróleo e Gás , Rádio (Elemento)/análise , Poluentes Radioativos da Água/análise , Bário/análise , Sulfato de Bário/química , Brasil , Precipitação Química , Rádio (Elemento)/química , Contagem de Cintilação , Poluentes Radioativos da Água/químicaRESUMO
An automatic system based on multisyringe flow injection analysis (MSFIA) and lab-on-valve (LOV) flow techniques for separation and pre-concentration of (226)Ra from drinking and natural water samples has been developed. The analytical protocol combines two different procedures: the Ra adsorption on MnO2 and the BaSO4 co-precipitation, achieving more selectivity especially in water samples with low radium levels. Radium is adsorbed on MnO2 deposited on macroporous of bead cellulose. Then, it is eluted with hydroxylamine to transform insoluble MnO2 to soluble Mn(II) thus freeing Ra, which is then coprecipitated with BaSO4. The (226)Ra can be directly detected in off-line mode using a low background proportional counter (LBPC) or through a liquid scintillation counter (LSC), after performing an on-line coprecipitate dissolution. Thus, the versatility of the proposed system allows the selection of the radiometric detection technique depending on the detector availability or the required response efficiency (sample number vs. response time and limit of detection). The MSFIA-LOV system improves the precision (1.7% RSD), and the extraction frequency (up to 3 h(-1)). Besides, it has been satisfactorily applied to different types of water matrices (tap, mineral, well and sea water). The (226)Ra minimum detectable activities (LSC: 0.004 Bq L(-1); LBPC: 0.02 Bq L(-1)) attained by this system allow to reach the guidance values proposed by the relevant international agencies e.g. WHO, EPA and EC.
Assuntos
Radiometria/métodos , Rádio (Elemento)/isolamento & purificação , Poluentes Radioativos da Água/isolamento & purificação , Rádio (Elemento)/análise , Contagem de Cintilação , Poluentes Radioativos da Água/análiseRESUMO
The investigation of scintillation properties of europium doped yttrium orthovanadate shows the suitability of this material for fiber-based dose rate measurements. All measurements were carried out with a 6 MV Varian linear accelerator. The temperature dependence of the signal is lower than that of the plastic scintillators reported so far. By measuring the afterglow of probes between Linac-pulses, the signal due to the stem effect can be successfully eliminated. Comparison of depth dose profiles in a water phantom for radiation field dimensions between 1 x 1 cm(2) and 10 x 10 cm(2) shows that the probes are suitable for small fields having dimensions up to 1 x 1 cm(2). The high light yield of probes having dimensions of 1 mm opens up the possibility for their use in spatially confined radiation fields, such as in intensity-modulated radiotherapy (IMRT) and volume-modulated radiation therapy (VMAT).
Assuntos
Európio/efeitos da radiação , Tecnologia de Fibra Óptica/instrumentação , Fótons , Radioterapia Conformacional/métodos , Contagem de Cintilação/instrumentação , Ítrio/efeitos da radiação , Relação Dose-Resposta à Radiação , Desenho de Equipamento , Análise de Falha de Equipamento , Európio/química , Tecnologia de Fibra Óptica/métodos , Teste de Materiais , Aceleradores de Partículas , Pós , Doses de Radiação , Contagem de Cintilação/métodos , Vanadatos , Ítrio/químicaRESUMO
Presently, two nuclear power plants operate in Brazil. Both are located at Itaorna beach, Angra dos Reis, approximately 133 km from Rio de Janeiro city. The reactor cooling circuits require the input of seawater, which is later discharged through a pipeline into the adjacent Piraquara de Fora Cove. The radioactive effluents undergo ion-exchange treatment prior to their release in batches, causing the enrichment of (3)H relative to other radionuclides in the discharged waters. Under steady state conditions, the (3)H gradient in the Piraquara de Fora waters can be used to determine the dependence of the dilution factor on the distance from the discharge point. The present work describes experiments carried out at the reactor site during batch release episodes, including time series sampling at the discharge point and surface seawater sampling every 250 m to a distance of 1250 m, after a double distillation, the (3)H concentration was measured by liquid scintillation counting applying a Quantulus liquid scintillation spectrometer. The obtained results showed a linear relationship between the (3)H concentration and distance from the discharge point. At 1250 m from the discharge point a dilution index of 1:15 was measured which fits the expected value based on modeling.
Assuntos
Centrais Nucleares , Água do Mar/análise , Trítio/análise , Poluentes Radioativos da Água/análise , Brasil , Monitoramento de Radiação , Contagem de CintilaçãoRESUMO
Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems greater in fliers than in nonfliers, although that conclusion rests mainly on a comparison of flying birds and nonflying mammals because only two frugivorous bat species have been studied. Furthermore, the bats studied so far were relatively large (>85 g, compared with most bat species which are <20 g) and were not insectivores (like about 70 % of bat species). We studied the small (11 g) insectivorous bat Tadarida brasiliensis and tested the prediction that the capacity for paracellular absorption would be as high as in the other bat and avian species studied so far, well above that in terrestrial, nonflying mammals. Using standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption = f) of inert carbohydrate probes: L-arabinose (MM = 150.13) absorbed exclusively by paracellular route and 3OMD-glucose (MM = 194) absorbed both paracellularly and transcellularly. As predicted, the capacity of paracellular absorption in this insectivorous bat was high (L-arabinose f = 1.03 ± 0.14) as in other frugivorous bats and small birds. Absorption of 3OMD-glucose was also complete (f = 1.09 ± 0.17), but >80 % was accounted for by paracellular absorption. We conclude that passive paracellular absorption of molecules of the size of amino acids and glucose is extensive in this bat and, generally in bats, significantly higher than that in nonflying mammals, although the exact extent can be somewhat lower or higher depending on molecule size, polarity and charge.
Assuntos
Quirópteros/fisiologia , Voo Animal/fisiologia , Absorção Intestinal/fisiologia , Análise de Variância , Animais , Arabinose/farmacocinética , Área Sob a Curva , Quirópteros/metabolismo , Cromatografia Líquida de Alta Pressão , Fluorescência , Glucose/farmacocinética , Contagem de Cintilação , Especificidade da EspécieRESUMO
The main interest of this study is to assess whether uranium deposits located in the San Marcos outcrops (NW of Chihuahua City, Mexico) could be considered as a source of U-isotopes in its surrounding environment. Uranium activity concentrations were determined in biota, ground, and surface water by either alpha or liquid scintillation spectrometries. Major ions were analyzed by ICP-OES in surface water and its suspended matter. For determining uranium activity in biota, samples were divided in parts. The results have shown a possible lixiviation and infiltration of uranium from geological substrate into the ground and surface water, and consequently, a transfer to biota. Calculated annual effective doses by ingestion suggest that U-isotopes in biota could not negligibly contribute to the neighboring population dose. By all these considerations, it is concluded that in this zone there is natural enhancement of uranium in all environmental samples analyzed in the present work.