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.
Abstract Day-boundary discontinuities at 00:00 in daily GNSS orbit and clock products can introduce nanosecond-level jumps into precise point positioning (PPP) clock estimates and degrade the continuity of station-to-station time transfer. Leveraging recently released “0 to 0” products, this study proposes a new processing strategy that explicitly uses the precisely determined day-boundary jumps. The method first computes the satellite-wise orbit and clock discontinuities at 00:00 from two consecutive “0 to 0” files, then distributes these jumps over a short correction interval on the second day and applies a small process noise to the ionosphere-free ambiguities so that they gradually absorb the residual boundary-induced errors. The approach is implemented within a PPP time-transfer framework and evaluated using 31 days of COD final and GBM rapid products, together with GPS and Galileo observations from four IGS stations forming three time-transfer links. Conventional PPP processing produces clock jumps ranging from less than 1 ns to approximately 6 ns. The proposed method effectively removes these discontinuities while preserving subsequent clock variations. For the three links, the mean absolute difference between the results at 00:00:00 and 00:00:30 decreases from 0.056-0.225 ns to 0.012-0.027 ns, corresponding to reductions of approximately 79-93%. The corrected results are also consistent with COD precise receiver-clock products within 1 ns. These findings demonstrate that the proposed strategy provides a practical way to achieve nanosecond-level continuity across day boundaries in GNSS-based time transfer.
Abstract Ultraviolet radiation is becoming increasingly popular for applications such as germicidal disinfection and photo-polymer additive manufacturing. However, calibrations of UV detectors have been limited by relative expanded uncertainties typically larger than 2% and a lack of National Measurement Institutes that measure wavelengths from 200 nm to 250 nm because of the difficulty working in that range. The National Institute of Standards and Technology (NIST) has established a new facility that achieves diode-to-diode spectral power responsivity transfers with uncertainties of 0.1% or better across the 200 nm to 400 nm wavelength range and a relative expanded uncertainty ( k =2) of less than 1%. The Ultraviolet Spectral Comparator Facility (UVSCF) provides spectral power and spectral irradiance responsivity calibrations of detectors and filter radiometers from 200 nm to 1800 nm. Its low UV transfer uncertainties derive from a combination of common-mode rejection, nitrogen purging the ozone from the system, a careful selection of mirrors, and strategic usage of broadband optical radiation sources, including a laser-driven light source and a deuterium lamp. The measurement stability over long time periods enables spatial mapping of detectors’ responsivities using calibrated x-y motion stages, which allows the facility to directly calibrate the spectral irradiance responsivity. Spectral irradiance is a critical measurement in many UV applications, and legacy calibration methods for spectral irradiance require multiple facilities and measurements. Our detector-based spectral irradiance responsivity method determines the spectral irradiance responsivity of silicon carbide detectors with 1% relative expanded uncertainty ( k =2). Those results agreed to within 0.70% with spectrally integrated irradiance measurements using a calibrated deuterium lamp with an independent scale traceability. This novel comparison of UVC scales validates the performance and uncertainties of the UVSCF and the efficacy of scanning spectral irradiance calibrations down to 200 nm.
