RESUMEN
The Standard Thermal Neutron Flux Unit, TNF2, in (LNMRI/IRD)(1, 2), was built for neutron detector and survey meter calibrations. The facility's fluence is achieved by moderation of four 241Am-Be with a graphite core and paraffin/graphite blocks surrounding it. Due to the small channel dimensions, it is impossible to calibrate personal dosemeters and survey meters for thermal neutrons. A polyethylene filter construction was carried out to allow the external irradiation of personal dosemeters and neutron survey meters. The polyethylene filter was constructed with 29 stacked discs with diameters ranging from 5 to 34 cm. Different thicknesses were simulated to provide the desired effect. This new irradiation configuration was also experimentally tested and compared with simulation results with MCNPX(3).
Asunto(s)
Grafito , Protección Radiológica , Polietileno , Americio/análisis , Método de Montecarlo , Protección Radiológica/métodos , NeutronesRESUMEN
Metrobras, a private company in Brazil, is developing a new laboratory for the calibration of neutron detectors in collaboration with the National Laboratory for Metrology of Ionizing Radiation (LNMRI). This work aimed at assessing neutron spectra, ambient dose equivalent rates, and neutron scattering in the calibration room of Metrobras Neutron Detectors Calibration Laboratory (LCDNM) using Monte Carlo simulation with MCNP5. Three models were simulated: vacuum, air, and the complete with the several materials employed in the actual room. Neutron spectra as a function of the distance from the source were obtained, compared, and used to calculate ambient dose equivalent at different points in the calibration room and results were compared to other neutron laboratories. Results show that LCDNM ambient dose equivalent rates are comparable to those of other neutron laboratories with 531.2 µSv . h-1 at 100 cm from the 592 GBq activity 241AmBe source. This work shows that LCDNM may be used as a calibration laboratory for neutron detectors in accordance with ISO 8529.
Asunto(s)
Laboratorios , Protección Radiológica , Americio/análisis , Brasil , Calibración , Simulación por Computador , Método de Montecarlo , Neutrones , Dosis de Radiación , Protección Radiológica/métodosRESUMEN
A long counter detector was manufactured by the Institute of Advanced Studies (IEAV) and was characterised in the neutron low scattering room at Brazilian National Ionising Radiation Metrology Laboratory (LNMRI/IRD) to deploy a secondary Standard for neutron fluence. The effective centre was measured experimentally with 252Cf+D2O, 252Cf, 241AmBe and 238PuBe neutron sources, having average energies from 0.55 to 4.16 MeV. The experimental arrangement and detector construction were carefully reproduced in Monte Carlo simulations, and the computational results were found to be in good agreement with those from experiment.
Asunto(s)
Americio/normas , Berilio/normas , Californio/normas , Laboratorios/normas , Neutrones , Plutonio/normas , Monitoreo de Radiación/normas , Protección Radiológica/normas , Americio/análisis , Berilio/análisis , Calibración , Californio/análisis , Método de Montecarlo , Plutonio/análisis , Dosis de RadiaciónRESUMEN
Occupational neutron fields usually have energies from the thermal range to some MeV and the characterization of the spectra is essential for estimation of the radioprotection quantities. Thus, the spectrum must be unfolded based on a limited number of measurements. This study implemented an algorithm based on the bee colonies behavior, named Artificial Bee Colony (ABC), where the intelligent behavior of the bees in search of food is reproduced to perform the unfolding of neutron spectra. The experimental measurements used Bonner spheres and 6LiI (Eu) detector, with irradiations using a thermal neutron flux and three reference fields: 241Am-Be, 252Cf and 252Cf (D2O). The ABC obtained good estimation of the expected spectrum even without previous information and its results were closer to expected spectra than those obtained by the SPUNIT algorithm.
Asunto(s)
Algoritmos , Conducta Apetitiva , Abejas , Neutrones , Monitoreo de Radiación/instrumentación , Protección Radiológica/instrumentación , Americio/análisis , Animales , Berilio/análisis , Biomimética , Californio/análisis , Simulación por Computador , Método de Montecarlo , Dosis de Radiación , Monitoreo de Radiación/métodosRESUMEN
The standard thermal neutron flux unit, TNF2, in the Brazilian National Ionizing Radiation Metrology Laboratory was rebuilt. Fluence is still achieved by moderating of four 241Am-Be sources with 0.6 TBq each. The facility was again simulated and redesigned with graphite core and paraffin added graphite blocks surrounding it. Simulations using the MCNPX code on different geometric arrangements of moderator materials and neutron sources were performed. The resulting neutron fluence quality in terms of intensity, spectrum and cadmium ratio was evaluated. After this step, the system was assembled based on the results obtained from the simulations and measurements were performed with equipment existing in LNMRI/IRD and by simulated equipment. This work focuses on the characterization of a central chamber point and external points around the TNF2 in terms of neutron spectrum, fluence and ambient dose equivalent, H*(10). This system was validated with spectra measurements, fluence and H*(10) to ensure traceability.
Asunto(s)
Americio/normas , Berilio/normas , Laboratorios/normas , Neutrones , Monitoreo de Radiación/normas , Protección Radiológica/normas , Americio/análisis , Berilio/análisis , Calibración , Método de Montecarlo , Dosis de RadiaciónRESUMEN
A TLD-based dosimeter of polyethylene-lead-polyethylene, was developed and characterized with Monte Carlo simulations, using the MCNPX code. This passive system for the determination of the ambient dose equivalent (H*(10)) for neutrons over a wide energy range can be used for the dosimetry of neutrons from atmospheric cosmic radiation, on the ground, and onboard aircraft. A method assisted by Monte Carlo simulations that improves the calibration of fast neutron dosimeters based on moderation and thermalization of the incident fast flux and the measurement of the thermal flux by a sensor, which respond mainly to thermal neutrons, is presented in this work. The H*(10) energy response of this dosimeter was obtained from simulations for monoenergetic neutrons from 10-10 to 104 MeV. The validation of the modeling was done with irradiations for ISO standard neutron fields of 241Am-Be, 252Cf and 252Cf(D2O) at Instituto de Radioproteção e Dosimetria (IRD, Brazil) and at CERN-EU high-energy reference field (CERF).
Asunto(s)
Americio/análisis , Californio/análisis , Radiación Cósmica , Neutrones , Dosímetros de Radiación , Monitoreo de Radiación/métodos , Protección Radiológica/métodos , Simulación por Computador , Método de Montecarlo , Dosis de RadiaciónRESUMEN
The Laboratório de Ciências Radiológicas is developing an irradiator for neutron survey meters calibration. Part of this work is related to the characterization of the neutron source that will be used in the irradiator. Therefore, a source of 241Am-Be(α,n) was characterized according to the following attributes: neutron energy distribution, anisotropy and emission rate. In order to make these values into high-level metrological references traceable by the Bureau International des Poids et Mesures, these measurements were taken at the Neutron Laboratory part of the Laboratório Nacional de Metrologia das Radiações Ionizantes. Results obtained for the source spectrum have strong adherence to the reference spectrum established by ISO 8529-1. The new laboratory for neutron calibration will allow calibration in an approximate ambient dose equivalent ranging 20-4500 µSv/h.
Asunto(s)
Partículas alfa , Americio/análisis , Americio/normas , Laboratorios/normas , Monitoreo de Radiación/normas , Protección Radiológica/normas , Dosis de RadiaciónRESUMEN
The objective of this work is to obtain fluence to effective dose conversion coefficients for neutron point sources, using the GEANT4 toolkit. These calculations aim to investigate the aspects of neutron transport in the human body through Monte Carlo simulation using the International Commission on Radiological Protection (ICRP) voxel phantoms, described in its publication 110. A benchmarking of the code was made for the case of monoenergetic plane parallel neutron beam in the antero-posterior (AP) irradiation geometry and organ absorbed dose conversion coefficients were compared with those found in the ICRP publication 116. The results showed good agreement with ICRP results in the studied energy range. Conversion coefficients were presented for specific conditions with 241Am-Be and 252Cf point neutron sources 1 m away from the phantom in the AP geometry.
Asunto(s)
Modelos Biológicos , Neutrones , Fantasmas de Imagen , Protección Radiológica/métodos , Radiometría/métodos , Recuento Corporal Total/métodos , Americio/análisis , Antropometría , Carga Corporal (Radioterapia) , Californio/análisis , Simulación por Computador , Humanos , Dosis de Radiación , Efectividad Biológica RelativaRESUMEN
After almost fifteen years of successful waste disposal operations, the first unambiguous airborne radiation release from the Waste Isolation Pilot Plant (WIPP) was detected beyond the site boundary on February 14, 2014. It was the first accident of its kind in the 15-year operating history of the WIPP. The accident released moderate levels of radioactivity into the underground air. A small but measurable amount of radioactivity also escaped to the surface through the ventilation system and was detected above ground. The dominant radionuclides released were americium and plutonium, in a ratio consistent with the known content of a breached drum. The radiation release was caused by a runaway chemical reaction inside a transuranic (TRU) waste drum which experienced a seal and lid failure, spewing radioactive materials into the repository. According to source-term estimation, approximately 2 to 10Ci of radioactivity was released from the breached drum into the underground, and an undetermined fraction of that source term became airborne, setting off an alarm and triggering the closure of seals designed to force exhausting air through a system of filters including high-efficiency-particulate-air (HEPA) filters. Air monitoring across the WIPP site intensified following the first reports of radiation detection underground to determine the extent of impact to WIPP personnel, the public, and the environment, if any. This article attempts to compile and interpret analytical data collected by an independent monitoring program conducted by the Carlsbad Environmental Monitoring & Research Center (CEMRC) and by a compliance-monitoring program conducted by the WIPP's management and operating contractor, the Nuclear Waste Partnership (NWP), LLC., in response to the accident. Both the independent and the WIPP monitoring efforts concluded that the levels detected were very low and localized, and no radiation-related health effects among local workers or the public would be expected.
Asunto(s)
Contaminantes Radiactivos del Aire/análisis , Residuos Radiactivos/análisis , Radioisótopos/análisis , Americio/análisis , New Mexico , Plutonio/análisis , Monitoreo de RadiaciónRESUMEN
After almost 15 years of operations, the Waste Isolation Pilot Plant (WIPP) had one of its waste drums breach underground as a result of a runaway chemical reaction in the waste it contained. This incident occurred on February 14, 2014. Moderate levels of radioactivity were released into the underground air. A small portion of the contaminated underground air also escaped to the surface through the ventilation system and was detected approximately 1 km away from the facility. According to the source term estimation, the actual amount of radioactivity released from the WIPP site was less than 1.5 mCi. The highest activity detected on the surface was 115.2 µBq/m(3) for (241)Am and 10.2 µBq/m(3) for (239+240)Pu at a sampling station located 91 m away from the underground air exhaust point and 81.4 µBq/m(3) of (241)Am and 5.8 µBq/m(3) of (239+240)Pu at a monitoring station located approximately 1 km northwest of the WIPP facility. The dominant radionuclides released were americium and plutonium, in a ratio that matches the content of the breached drum. Air monitoring across the WIPP site intensified following the first reports of radiation detection underground to determine the extent of impact to WIPP personnel, the public, and the environment. In this paper, the early stage monitoring data collected by an independent monitoring program conducted by the Carlsbad Environmental Monitoring & Research Center (CEMRC) and an oversight monitoring program conducted by the WIPP's management and operating contractor, the Nuclear Waste Partnership (NWP) LLC were utilized to estimate the actual amount of radioactivity released from the WIPP underground. The Am and Pu isotope ratios were measured and used to support the hypothesis that the release came from one drum identified as having breached that represents a specific waste stream with this radionuclide ratio in its inventory. This failed drum underwent a heat and gas producing reaction that overpowered its vent and lifted its lid to allow release of waste into the underground air.
Asunto(s)
Contaminantes Radiactivos del Aire/análisis , Americio/análisis , Plutonio/análisis , Monitoreo de Radiación , Liberación de Radiactividad Peligrosa , Residuos Radiactivos/análisis , New Mexico , RadiactividadRESUMEN
The Brazilian Instituto de Radioproteção e Dosimetria (IRD) runs a neutron individual monitoring system with a home-made TLD albedo dosemeter. It has already been characterised and calibrated in some reference fields. However, the complete energy response of this dosemeter is not known, and the calibration factors for all monitored workplace neutron fields are difficult to be obtained experimentally. Therefore, to overcome such difficulties, Monte Carlo simulations have been used. This paper describes the simulation of the HP(10) neutron response of the IRD TLD albedo dosemeter using the MCNPX transport code, for energies from thermal to 20 MeV. The validation of the MCNPX modelling is done comparing the simulated results with the experimental measurements for ISO standard neutron fields of (241)Am-Be, (252)Cf, (241)Am-B and (252)Cf(D2O) and also for (241)Am-Be source moderated with paraffin and silicone. Bare (252)Cf are used for normalisation.
Asunto(s)
Dosis de Radiación , Dosímetros de Radiación , Monitoreo de Radiación/instrumentación , Protección Radiológica/instrumentación , Dosimetría Termoluminiscente/métodos , Algoritmos , Americio/análisis , Berilio/análisis , Boro/análisis , Brasil , Calibración , Californio/análisis , Simulación por Computador , Humanos , Ensayo de Materiales , Método de Montecarlo , Neutrones , Exposición Profesional/análisis , Parafina/química , Monitoreo de Radiación/métodos , Protección Radiológica/métodos , Sensibilidad y Especificidad , Silicio/química , Programas InformáticosRESUMEN
Radioactive lightning rods (RLR) were manufactured and installed in Brazil for almost two decades, before they were prohibited in 1989. Structures protected by this type of lightning preventers included residential buildings, schools, commercial and industrial facilities, among others. It is estimated that about 3.4 TBq of 241Am were used by manufacturers, and a total of 75,000 pieces with a mean activity of about 46 MBq were in the market. While only a fraction of the total has been recovered, the almost twenty thousand pieces already collected at the Nuclear and Energy Research Institute (IPEN) had their sources successfully separated from the remaining recyclable metal scrap and are now encapsulated in lead containers for final disposal.
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Americio/efectos adversos , Residuos Radiactivos , Administración de Residuos , Americio/análisis , Brasil , Humanos , Relámpago , Monitoreo de Radiación/métodos , Protección Radiológica/métodos , Residuos Radiactivos/efectos adversos , Residuos Radiactivos/análisis , Administración de Residuos/métodosRESUMEN
The National Laboratory for Metrology of Ionizing Radiation (LNMRI)/Brazil acquired (166m)Ho and (243)Am/(239)Np solutions from commercial suppliers in order to realize primary standardization and therefore reducing the associated uncertainties. The method used in the standardization was the live-timed 4πß(LS)-γ(ΝaI(Tl)) anticoincidence counting. The live-timed anticoincidence system is operated since 2006 in LNMRI and is composed of two MTR2 modules donated by Laboratoire National Henri Becquerel (LNE-LNHB)/France. The data acquisition system uses a homemade LabView program and an Excel file for calculus. These systems have been used for primary standardization at LNMRI for many radionuclides and recently took part in the (124)Sb and (177)Lu International Key Comparisons with good performance.
Asunto(s)
Americio/análisis , Americio/normas , Holmio/normas , Neptunio/análisis , Neptunio/normas , Radiometría/normas , Programas Informáticos/normas , Americio/química , Brasil , Semivida , Holmio/análisis , Internacionalidad , Lenguajes de Programación , Dosis de Radiación , Estándares de Referencia , Valores de ReferenciaRESUMEN
With the aim of improving the monitoring of workers potentially exposed to neutron radiation in Brazil, the IPEN/CNEN-SP in association with PRO-RAD designed and developed a passive individual gamma-neutron mixed-field dosemeter calibrated to be used to (241)AmBe sources. To verify the dosimetry system response to different neutron spectra, prototypes were irradiated with a (252)Cf source and evaluated using the dose-calculation algorithm developed for (241)AmBe sources.
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Americio/análisis , Berilio/análisis , Californio/análisis , Monitoreo de Radiación/instrumentación , Protección Radiológica/instrumentación , Radiometría/instrumentación , Algoritmos , Brasil , Calibración , Interpretación Estadística de Datos , Rayos gamma , Humanos , Neutrones , Dosis de Radiación , Monitoreo de Radiación/métodos , Protección Radiológica/métodos , Radiometría/métodos , TemperaturaRESUMEN
In this paper results of X-ray and gamma-ray emission probabilities per decay of (51)Cr and (241)Am are presented. The measurements were carried out by means of HPGe planar and REGe spectrometers. The activity of (51)Cr and (241)Am samples was determined in a 4pibeta-gamma coincidence counting system. The HPGe spectrometers were calibrated in a well defined geometry by means of (54)Mn, (55)Fe, (57)Co, (133)Ba, (152)Eu, (166m)Ho and (241)Am sources, previously standardized in a 4pibeta-gamma coincidence system. The MCNP Monte Carlo code was used for simulation of the REGe spectrometer calibration curve, for the selected geometry, and compared with the experimental curve. The experimental results were compared with data from literature.
Asunto(s)
Americio/análisis , Radioisótopos de Cromo/análisis , Radiometría/métodos , Espectrometría gamma/métodos , Americio/química , Radioisótopos de Cromo/química , Interpretación Estadística de Datos , Rayos gamma , Semivida , Dosis de Radiación , Rayos XRESUMEN
Radioactive lightning rods were manufactured in Brazil until 1989, when the licenses for using radioactive sources in these products were lifted by the national nuclear authority. Since then, these rods have been replaced by the Franklin type and collected as radioactive waste. However, only 20% of the estimated total number of installed rods has been delivered to the Brazilian Nuclear Commission. This situation causes concern, since there is the possibility of the rods to be disposed as domestic waste. In Brazil, 64% of the municipal solid waste is disposed at garbage dumps without sufficient control. In addition, (241)Am, the radionuclide most commonly employed, is classified as a high-toxicity element, when incorporated. In the present study, (241)Am migration experiments were performed by means of a lysimeter system, in order to evaluate the risk of contamination caused by radioactive lightning rods disposed as common solid waste. (241)Am sources removed from lightning rods were placed inside lysimeters filled with organic waste that was collected at the restaurant of the Instituto de Pesquisas Energéticas e Nucleares. The generated leachate was periodically analyzed, and characteristics such as pH, redox potential, solid content and the concentration of the radioactive material were determined. The equivalent dose for members of the public was calculated considering ingestion of contaminated drinking water as the major path of exposure. Estimated doses were about 20-times below the effective dose limit of 1 mSv year(-1) for members of the public as recommended by the International Commission on Radiological Protection. This suggests the radiation risk caused by lightning rods disposed at uncontrolled garbage dumps to be low. It should be noted, however, that the number of investigated lightning rods was quite small. The results of this study might therefore not be entirely representative and should be interpreted with care. They provide, however, a very first basis for characterizing the transfer of (241)Am from lightning rods to the human food chain.
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Americio/análisis , Contaminación Radiactiva de Alimentos/análisis , Residuos de Alimentos , Americio/efectos adversos , Brasil/epidemiología , Exposición a Riesgos Ambientales/efectos adversos , Sustancias Peligrosas/efectos adversos , Sustancias Peligrosas/análisis , Humanos , Residuos Industriales/efectos adversos , Residuos Industriales/análisis , Monitoreo de Radiación , Residuos Radiactivos/efectos adversos , Residuos Radiactivos/análisis , Radioisótopos/efectos adversos , Radioisótopos/análisis , Medición de Riesgo , Contaminantes Químicos del Agua/análisis , Contaminación Radiactiva del Agua/efectos adversos , Contaminación Radiactiva del Agua/análisisRESUMEN
The standardization of 241 Am solution has been undertaken using a 4pibeta-gamma coincidence system. The 4pi proportional counter used for alpha detection has a 0.1 mm thick Al window in the outside wall in order to minimize gamma-ray attenuation. The extrapolation technique was applied to determine the activity of the solution. The variation of alpha efficiency has been made using external absorbers and by the electronic discrimination. The results from the two methods were compared and are in agreement within the experimental uncertainty.
Asunto(s)
Algoritmos , Americio/análisis , Americio/normas , Radiometría/métodos , Radiometría/normas , Espectrometría gamma/métodos , Espectrometría gamma/normas , Brasil , Guías como Asunto , Dosis de Radiación , Estándares de Referencia , Valores de Referencia , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , SolucionesRESUMEN
This work aimed to determine the irradiator thermal (under-cadmium) and fast (over-cadmium) neutron fluxes, of the Nuclear Experimental Laboratory of the Nuclear Engineering Center (CNEN-IPEN, São Paulo, Brazil), and the possibility of this irradiator use for Neutron Activation Analysis (NAA), by the absolute method. To establish the facility specifications, the neutron flux values along the irradiator axis were determined experimentally and calculated by Monte Carlo method. The irradiator presents the advantage of supplying a stable neutron flux for a long period, eliminating the need to use standard material (comparative method), so that the process becomes agile, practical and economical.
Asunto(s)
Americio/análisis , Berilio/análisis , Diseño Asistido por Computadora , Neutrones , Aceleradores de Partículas/instrumentación , Radioisótopos/análisis , Radiometría/métodos , Diseño de Equipo/métodos , Análisis de Falla de Equipo/métodos , Modelos Estadísticos , Método de Montecarlo , Control de Calidad , Dosis de Radiación , Radiometría/instrumentación , Dispersión de Radiación , Programas InformáticosRESUMEN
A Monte Carlo program, Visual Monte Carlo (VMC) in vivo, was written to simulate photon transport through an anthropomorphic phantom and to detect radiation emitted from the phantom. VMC in vivo uses a voxel phantom provided by Yale University and may be used to calibrate in vivo systems. This paper shows the application of VMC in vivo to the measurement of 241Am deposited simultaneously in the thoracic region, the bones, the liver and in the rest of the body. The percentages of 241Am in the four body regions were calculated using the biokinetic models established by the ICRP, for a single intake via inhalation. The four regions of the voxel phantom were then 'contaminated' in accordance with the calculated percentages. The calibration factor of the in vivo system was then obtained. This procedure was repeated for the radionuclide distributions obtained 5, 30, 120, 240 and 360 days after intake. VMC in vivo was also used to calculate the calibration factor of the in vivo system in which the radionuclide was assumed to be deposited only in the lung, as is normally done. The activities calculated with the radionuclide distributed in the four body regions as a factor of time, and the activities calculated with the radionuclide deposited in the lung only are compared.
Asunto(s)
Americio/farmacocinética , Articulación de la Rodilla/metabolismo , Hígado/metabolismo , Pulmón/metabolismo , Modelos Biológicos , Modelos Estadísticos , Recuento Corporal Total/métodos , Americio/análisis , Simulación por Computador , Humanos , Exposición por Inhalación/análisis , Tasa de Depuración Metabólica , Método de Montecarlo , Especificidad de Órganos , Fantasmas de Imagen , Fotones , Dosis de Radiación , Recuento Corporal Total/normasRESUMEN
The Department of Energy has constructed a deep geologic repository for defense transuranic waste disposal. The Waste Isolation Pilot Plant, located in Southeastern New Mexico, is slated to receive transuranic waste by truck delivery beginning in 1998. The Environmental Evaluation Group (EEG) provides an independent evaluation of the impact on the health and environment in New Mexico of the WIPP project. Since 1985, the EEG has operated a network of air monitoring sites around WIPP and in nearby communities. The radionuclide concentration data from these air samples have been assembled into a useful baseline data base after resolution of a number of methodological and quality assurance issues. Investigation thresholds for the principal radionuclides have been calculated from combined data collected from several sites. These action levels will provide a critical quantitative basis for decisions of whether future airborne radionuclide measurements are attributable to accidental releases.