RESUMEN
Albedo dosemeters remain the most used dosemeters in neutron individual monitoring. In Brazil, most of the neutron occupational fields are from radionuclide sources, often without any moderation, where albedo dosemeters have poor energy response. The purpose of this work is to compare the HP(10) energy response of the IRD and ALNOR TLD albedo dosemeter systems, calculated by their modelling with Monte Carlo code MCNPX. Their energy responses are similar, as expected, but the IRD system is about five times more sensitive than the ALNOR one. IRD albedo system can measure the Brazilian monthly recording level of 0.2 mSv, even for bare 252Cf and 241Am-Be neutron fields. On the other hand, the ALNOR system can measure values higher than 0.2 mSv only after huge moderation of theses sources. These results show that IRD TLD albedo is more suitable than the ALNOR one to measure low doses at occupational fields from radionuclide sources.
Asunto(s)
Dosis de Radiación , Protección Radiológica/instrumentación , Dosimetría Termoluminiscente/instrumentación , Americio , Berilio , Brasil , Simulación por Computador , Diseño de Equipo , Método de Montecarlo , Neutrones , Dosímetros de Radiación , RadiometríaRESUMEN
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
The neutron scattering at the Low Scattering Laboratory of the Brazilian National Neutron Laboratory has been studied using three different methods. The measurements have been done with a traceable standard (241)Am-Be from source-to-detector distances of 0.52-3.00 m. The obtained results with the variation distance methods are in agreement. Measurements with a large shadow cone are not worth for larger distances due to overshadowing. As the quantity required in a calibration is the response of the device being calibrated to the scattered neutron component in order to subtract this from the total response, for these purposes, the distance variation method must be used for each device. To quantify absolutely the scattering contribution on the quantity rates of fluence, Hp(10) and H*(10) in irradiation procedures, a Bonner sphere spectrometer with the shadow cone was employed. The evaluated scattering correction factor value may be employed for a distance of 1.00 m.
Asunto(s)
Neutrones , Protección Radiológica/instrumentación , Radiometría/instrumentación , Dispersión de Radiación , Algoritmos , Americio , Berilio , Brasil , Calibración , Dosis de Radiación , Protección Radiológica/métodos , Radiometría/métodos , Reproducibilidad de los Resultados , EspectrofotometríaRESUMEN
The Monte Carlo program 'Visual Monte Carlo-dose calculation' (VMC-dc) uses a voxel phantom to simulate the body organs and tissues, transports photons through this phantom and reports the absorbed dose received by each organ and tissue relevant to the calculation of effective dose as defined in ICRP Publication 60. This paper shows the validation of VMC-dc by comparison with EGSnrc and with a physical phantom containing TLDs. The validation of VMC-dc by comparison with EGSnrc was made for a collimated beam of 0.662 MeV photons irradiating a cube of water. For the validation by comparison with the physical phantom, the case considered was a whole body irradiation with a point 137Cs source placed at a distance of 1 m from the thorax of an Alderson-RANDO phantom. The validation results show good agreement for the doses obtained using VMC-dc and EGSnrc calculations, and from VMC-dc and TLD measurements. The program VMC-dc was then applied to the calculation of doses due to immersion in water containing gamma emitters. The dose conversion coefficients for water immersion are compared with their equivalents in the literature.