The measurements of high-contrast scenes, where there are very different levels of luminance simultaneously, is necessary for a growing number of applications in lighting. For evaluating this kind of scene, high-dynamic-range (HDR) measurements with imaging systems are required. A methodology must be established and verified to provide traceable HDR luminance measurements. A measurement model for these measurements is proposed and described, which allows traceability of HDR luminance measurements with imaging systems. This model includes the variables that need to be considered to properly evaluate the uncertainty of the measurement. The uncertainty is derived analytically from the measurement model for luminance measured at individual pixels, and the propagation of this uncertainty is considered when the average luminance across several pixels needs to be measured, including the correlations of the errors at different pixels and luminous sources in the scene. This analytical approach to the evaluation of uncertainty is important for understanding the impact of the different sources of uncertainties. The Monte Carlo approach, which is simpler and easier to implement, is also presented and discussed.
Abstract In defined solid-angle (DSA) alpha counting for the primary standardisation of Radon-222 activity, cryogenic operation can modify the measurement geometry through thermomechanical deformation of the source assembly and changes in the potential extent of the deposited source. Coupled heat-transfer and thermomechanical finite-element simulations were used to investigate the influence of nickel support rod length on the source–diaphragm distance and on the radial region in which Radon-222 condensation is thermodynamically possible. Thermomechanical deformation was found to be the dominant contribution to the uncertainty of the source–diaphragm distance for the investigated configurations. Shortening the support rod reduced this contribution but increased the thermally affected source radius. These effects were propagated to the geometry factor using a GUM-compliant uncertainty analysis. Under the assumed uncertainties of the investigated geometrical parameters, the calculated relative combined standard uncertainty associated with the geometry factor decreases from approximately 0.16% for a 120 mm support rod to approximately 0.03% for a 5 mm rod. The results provide quantitative guidance for optimising cryogenic DSA source assemblies, while a complete uncertainty evaluation of the primary Radon-222 standardisation requires consideration of the actual spatial distribution of deposited activity and other measurement-model contributions.
Abstract A common understanding of measurement data is fundamental to our society and the Système International (SI) is a central foundation in that regard. To prepare the SI for upcoming decades, its underpinning knowledge model needs to be accessible by software agents for interoperable use of measurement data. In this work, the knowledge model is extracted from the SI Brochure and implemented using Semantic Web standards. In addition, web services are developed around the knowledge model to showcase and simplify the use of the developed ontology. The quality of the implementation is tested based on key questions which the knowledge model will be expected to answer.
Abstract The first half-value layer (HVL), defined as the thickness of material required to reduce the x-ray beam intensity (air kerma) to 50%, is a key radiation quality specifier. Although HVL has been measured for decades using ionization chambers and aluminum filters, the detailed measurement procedures and associated uncertainties remain insufficiently established. With the growing use of x-ray multimeters (XMMs) capable of measuring HVL directly from the x-ray beam, reliable calibration and uncertainty evaluation are needed. This work presents a detailed approach for determining the first HVL and calibrating XMMs for RQR 2, RQR 5, and RQR 10 standard radiation qualities for radiography as defined in IEC 61 267. The uncertainty budget is structured into three steps: measured HVL, reference HVL, and HVL calibration coefficient, emphasizing the effects of ionization chamber energy dependence and field size. The reference HVLs for RQR 2, RQR 5, and RQR 10 were 1.417 mm Al, 2.570 mm Al, and 6.510 mm Al, respectively, with expanded uncertainties ( k = 2) of 1.0%, 1.1%, and 1.7%. The corresponding HVL calibration coefficients had uncertainties of 1.4%, 1.3%, and 1.8%.
Abstract 4πγ counting is an important method for radionuclide activity standardization, with relatively simple source preparation and experimental operation. However, its accuracy depends strongly on the calculated nuclide-specific total detection efficiency. The efficiency calculation involves numerous input quantities, including detector dimensions, material properties, source geometry, nuclear decay data, photon interaction cross sections, and energy threshold. A comprehensive evaluation of the uncertainties associated with these inputs therefore remains challenging. Detailed particle-transport simulations provide considerable flexibility in efficiency calculations, but become computationally intensive when embedded in a Monte Carlo uncertainty propagation procedure. In this study, the framework described in Supplement 1 to the Guide to the Expression of Uncertainty in Measurement was implemented for 4πγ counting using a custom-built well-type NaI(Tl) detector. The principal input uncertainties were propagated through detailed particle-transport simulations based on a Geant4 model for 134 Cs and 137 Cs. The convergence of the estimated efficiency uncertainty with the number of trials was examined, and 4000 trials were adopted for each calculation. The relative standard uncertainties of the calculated total detection efficiencies were 0.15% and 0.64% for 134 Cs and 137 Cs, respectively. Activity concentrations determined by 4πγ counting agreed with independent results obtained by 4πβ(PC)–γ coincidence counting and efficiency tracing. This implementation provides a practical means of evaluating detection-efficiency uncertainty in 4πγ counting based on detailed particle-transport simulations.
