RESUMEN
The Health Physics Measurements Group at the Los Alamos National Laboratory (LANL) has initiated a study of neutron reference fields at selected US Department of Energy (DOE) calibration facilities. To date, field characterisation has been completed at five facilities. These fields are traceable to the National Institute for Standards and Technology (NIST) through either a primary calibration of the source emission rate or through the use of a secondary standard. However, neutron spectral variation is caused by factors such as room return, scatter from positioning tables and fixtures, source anisotropy and spectral degradation due to source rabbits and guide tubes. Perturbations from the ideal isotropic point source field may impact the accuracy of instrument calibrations. In particular, the thermal neutron component of the spectrum, while contributing only a small fraction of the conventionally true dose, can contribute a significant fraction of a dosemeter's response with the result that the calibration becomes facility-specific. A protocol has been developed to characterise neutron fields that relies primarily on spectral measurements with the Bubble Technology Industries (BTI) rotating neutron spectrometer (ROSPEC) and the LANL Bonner sphere spectrometer. The ROSPEC measurements were supplemented at several sites by the BTI Simple Scintillation Spectrometer probe, which is designed to extend the ROSPEC upper energy range from 5 to 15 MeV. In addition, measurements were performed with several rem meters and neutron dosemeters. Detailed simulations were performed using the LANL MCNPX Monte Carlo code to calculate the magnitude of source anisotropy and scatter factors.
Asunto(s)
Agencias Gubernamentales , Neutrones , Radiometría/normas , Valores de Referencia , Calibración , Dosis de Radiación , Estados UnidosRESUMEN
Initial calibration of a multisphere spectroscopy system has been completed at Los Alamos National Laboratory using four standard calibration scenarios. Spectrum unfolding was performed using three methods of constructing the default spectrum: simple parameter models, Monte Carlo calculations and physical measurement. Comparisons of the resulting spectra for each solution method are presented. Implications of the spectral solutions upon dosemeter characterisation are addressed.
Asunto(s)
Algoritmos , Análisis de Falla de Equipo/normas , Neutrones , Protección Radiológica/normas , Radiometría/normas , Medición de Riesgo/normas , Análisis Espectral/normas , Carga Corporal (Radioterapia) , Diseño de Equipo , Análisis de Falla de Equipo/métodos , Estudios de Factibilidad , Humanos , Transferencia Lineal de Energía , Método de Montecarlo , Dosis de Radiación , Protección Radiológica/instrumentación , Protección Radiológica/métodos , Radiometría/instrumentación , Radiometría/métodos , Estándares de Referencia , Efectividad Biológica Relativa , Reproducibilidad de los Resultados , Medición de Riesgo/métodos , Factores de Riesgo , Sensibilidad y Especificidad , Análisis Espectral/instrumentación , Análisis Espectral/métodos , Estados UnidosRESUMEN
The Los Alamos National Laboratory Model 8823 whole-body TLD has been designed to perform accurate dose estimates for beta, photon, and neutron radiations that are encountered in pure calibration, mixed calibration, and typical field radiation conditions. The radiation energies and field types for which the Model 8823 dosimeter is capable of measuring are described. The Model 8823 dosimeter has been accredited for all performance testing categories in the Department of Energy Laboratory Accreditation Program for external dosimetry systems. The philosophy used in the design of the Model 8823 dosimeter and the associated dose algorithm is to isolate the responses due to beta, photon, and neutron radiations; obtain radiation quality information; and make functional adjustments to the elemental readings to estimate the dose equivalent at 7, 300, and 1,000 mgcm(-2), representing the required repoting quantities for shallow, lens-of-the-eye, and deep dose, respectively.
Asunto(s)
Algoritmos , Modelos Teóricos , Dosis de Radiación , Dosimetría Termoluminiscente/instrumentación , Dosimetría Termoluminiscente/métodos , Partículas beta , Calibración , Diseño de Equipo , Guías como Asunto , Humanos , Neutrones , FotonesRESUMEN
Research efforts towards developing a new method for calibrating in vivo measurement systems using magnetic resonance imaging (MRI) and Monte Carlo computations are discussed. The method employs the enhanced three-point Dixon technique for producing pure fat and pure water MR images of the human body. The MR images are used to define the geometry and composition of the scattering media for transport calculations using the general-purpose Monte Carlo code MCNP, Version 4. A sample case for developing the new method utilizing an adipose/muscle matrix is compared with laboratory measurements. Verification of the integrated MRI-MCNP method has been done for a specially designed phantom composed of fat, water, air, and a bone-substitute material. Implementation of the MRI-MCNP method is demonstrated for a low-energy, lung counting in vivo measurement system. Limitations and solutions regarding the presented method are discussed.