Standard Uncertainty Research Articles

APMP/TCRI key comparison report of measurement of air kerma for medium-energy x-rays (APMP.RI(I)-K3.2013)

Main textThe APMP/TCRI Dosimetry Working Group initiated the APMP.RI(I)-K3.2013 key comparison of measurement of air kerma for medium-energy x-rays (100 kV to 250 kV); measurements took place between 2015 and 2017. In total, 11 institutes took part in the comparison, among which 8 were APMP member laboratories, two from AFRIMETS and one from SIM. Three commercial cavity ionization chambers were used as transfer standards circulated among the participants. All the participants established 100, 135, 180 and 250 kV x-ray beam qualities equivalent to those of the BIPM. The ARPANSA and the NMIJ were linking laboratories and two participants subsequently made comparisons with the BIPM. The 7 other participants' degrees of equivalence fell within 11 parts in 103 of unity, well within the relevant expanded uncertainty (k = 2) in all cases. Excluding the BARC, the results were within 5.7 parts in 103, well within the relevant combined standard uncertainty. These results indicated that the calibration capabilities of most laboratories were in very good agreement and there were no serious discrepancies between them. The effect of implementing the recommendations of ICRU Report 90, which occurred on 1 January 2018 (after this comparison), is discussed and we deduce that the effect on the degrees of equivalence is negligible. The increase in the uncertainty in Wair has been added to all laboratories so that the degrees of equivalence and the uncertainties published here are applicable to post-ICRU 90 measurement results.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Traceability Technology of DC Electric Energy Metering for On-Site Inspection of Chargers

The on-site inspection of high-power DC chargers results in new DC high-current measurement and DC energy traceability system requirements. This paper studies the traceability technology of electric energy value for automotive high-power DC chargers, including: (1) the traceability method of the built-in DC energy meter and shunt of the charger; (2) precision DC high current and small precision DC voltage output and measurement technology. This paper designs a 0.1 mA~600 A DC high current measurement system and proposes a 0.005 level DC power measurement traceability system. The uncertainty evaluation experiment of the DC power measurement calibration system and the high-power DC charger’s on-site calibration experiment results verify the method’s effectiveness and feasibility in this paper. The experimental results show that the combined standard uncertainty of the DC power metering verification system can be 0.0451%.

Improvements of the NIM-2 Joule Balance Since 2020

The joule balance, which relates the mechanical energy and the electrical energy, was proposed by National Institute of Metrology (NIM) to measure the Planck constant and realize the kilogram with the Planck constant based on the new definition of the kilogram. In 2019, the NIM-2 joule balance participated in the first key comparison of kilogram realizations (CCM.M-K8.2019) with a combined relative standard uncertainty of 4.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> . After the first key comparison, a series of improvements on the mechanical, electrical, and the alignment systems have been carried out. To improve the accuracy of the electrical measurement, the periodical calibration of the digital voltmeter (DVM) with the Programmable Josephson Voltage System (PJVS) was also realized. The calibration period of the DVM was reduced from 5 days to 3.5 hours. With these improvements, the corresponding uncertainties were decreased significantly.

Bilateral comparison of 1.018 V and 10 V standards between DEFNAT (Tunisia) and the BIPM, April to June 2022 (part of the ongoing BIPM key comparison BIPM.EM-K11.a and b)

Main textAs part of the ongoing BIPM key comparison BIPM.EM-K11.a and b, a comparison of the 1.018 V and 10 V voltage reference standards of the BIPM and the Laboratoire de Métrologie Électrique, DEFNAT (Tunisia), was carried out from April to June 2022. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_E (ZE) and BIPM_F (ZF), were transported by freight to DEFNAT to be measured and back to the BIPM for checking the stability of the traveling standards. At DEFNAT, the reference standard for DC voltage is a Josephson Voltage Standard (JVS). The output EMF (Electromotive Force) of each travelling standard was measured by direct comparison with the primary standard.The final result of the comparison is presented as the difference between the values assigned to DC voltage standards by DEFNAT, at the level of 1.018 V and 10 V, at DEFNAT, U DEFNAT, and those assigned by the BIPM, at the BIPM, U BIPM, at the reference date of the 15th of May 2022. U DEFNAT - U BIPM = 0.03 μV; u c = 0.03 μV, at 1.018 V U DEFNAT - U BIPM = 0.44 μV; u c = 0.12 μV, at 10 Vwhere u c is the combined standard uncertainty associated with the measured difference, including the uncertainty of the representation of the volt at the BIPM and at DEFNAT, based on K J, and the uncertainty related to the comparison.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K4 of the absorbed dose to water standards of the BFKH, Hungary and the BIPM in 60Co gamma radiation

Main textA new key comparison of the standards for absorbed dose to water of the Budapest Főváros Kormányhivatala (BFKH), Hungary, and the Bureau International des Poids et Mesures (BIPM) was carried out in the 60Co radiation beam of the BIPM in October 2021. The comparison result, based on the calibration coefficient for a transfer chamber and evaluated as a ratio of the BFKH and the BIPM standards for absorbed dose to water, is 0.9965 with a combined standard uncertainty of 4.5 parts in 103. The result agrees within the uncertainties with the comparison carried out in 2002. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database KCDB.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Key comparison BIPM.RI(I)-K1 of the air-kerma standards of the BFKH, Hungary and the BIPM in 60Co gamma radiation

Main textA new key comparison of the standards for air kerma of the Budapest Főváros Kormányhivatala (BFKH), Hungary and the Bureau International des Poids et Mesures (BIPM) was carried out in the 60Co radiation beam of the BIPM in October 2021. The comparison result, based on the calibration coefficients for a transfer chamber and expressed as a ratio of the BFKH and the BIPM standards for air kerma, is 1.0029 with a combined standard uncertainty of 2.2 parts in 103. The result agrees within the uncertainties with the comparison carried out in 2016. The results are analysed and presented in terms of degrees of equivalence, suitable for entry in the BIPM key comparison database.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Real-Time Correction of Gas Concentration in Nondispersive Infrared Sensor

Non-dispersive infrared (NDIR) sensors have been widely used in measuring gas concentration in process industry. However, the inhomogeneous gas diffusion in the gas chamber of NDIR sensor increases the response time and causes measurement error. In this case, the fast-and-accurate measurement of gas concentration is of great importance in avoiding accidents. This article focuses on constructing a novel gas diffusion model among normalization concentration (N-concentration), inlet flow velocity, and diffusion time. Firstly, the structure model of gas chamber is constructed based on Fluent 15.0 and the turbulence intensity is calculated based on dynamic viscosity, inlet flow velocity, concentration, temperature and pressure. The simulation model is constructed based on the assumption of simultaneous reaction and mass transfer. The initial result shows that the N-concentration along the optical path is mainly influenced by inlet flow velocity and diffusion time, while the temperature, pressure and inlet concentration have less influence on gas diffusion. According to the velocity distribution map, the critical zone of inlet flow velocity is defined to divide the gas diffusion state into different zones. Then, a novel Multi-interval exponential diffusion model is proposed to calculate the N-concentration and the real-time measurement of gas concentration can be achieved based on inlet flow velocity, diffusion time and the pre-defined critical zone of inlet flow velocity. The proposed model is suitable for the gas concentration correction of different gases. Finally, the validation indexes include the coefficient of determination (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), Mean Squared Error (MSE) and standard uncertainty shows the accuracy of the proposed model can be obviously increased.

COOMET regional comparison of the national standards of air kerma for x-radiation qualities used for radiation protection and diagnostic radiology (COOMET.RI(I)-S3)

Main textThe results of the COOMET supplementary comparison of the national measurement standards of air kerma for x-radiation qualities used for radiation protection and diagnostic radiology are presented. Nine National Metrology Institutes from the COOMET organization and the International Atomic Energy Agency participated in this COOMET project no.641. The BelGIM acted as a pilot laboratory. The comparison reference value (CRV) was obtained as the mean result of the PTB and the VNIIM. Almost all participants obtained valid results which were consistent within the relative standard uncertainties of the comparison ranging from 0.28% to 2.6%. Some participants had unacceptable results.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Type B uncertainty of two-channel measurements

The paper presents the problems of evaluating the standard uncertainty of measuring a quantity using the type B method, the result of which is the average value of the results obtained from two channels with the same parameters, for example, as the indications of two measuring instruments of the same type. It is shown that for given values of maximum permissible errors (MPE) of measuring instruments and their readings x1 and x2, the uncertainty of the result determined a posteriori is not equal to the uncertainty determined by the conventional method (GUM). It is shown that when the measurement result is determined as arithmetic mean y=(x1+x2)/2, additional information as the half distance of readings v=|x1-x2|/2 can be used to correctly determine the standard uncertainty of such measurement. Depending on the half distance of readings, the standard uncertainty can theoretically vary from its maximum value (the readings of both meters are equal) to zero (with maximum difference in readings). The analysis of the uncertainty was carried out for uniform distributions of possible deviations of the readings of measuring instruments within their MPE. The results of simulations by the modified Monte-Carlo method, which show good convergence with theoretical results, are given.

Evaluation of the measurement uncertainty during the tensile tests of high-strength bolts

A developed methodology for evaluating measurement uncertainty during the tensile tests of metals and alloys is presented. In this connection, the various sources of uncertainty are considered. The object of studies included high-strength bolts made of 40Kh “Selekt” steel, which were subjected to tensile tests according to the GOST 1497-85 State Standard using a UMM-100 universal tensile testing machine. The basic sources of uncertainty in the measurement of relative elongation and reduction were shown to include repeated measurements of relative elongation; errors of measuring the finite length by a vernier calliper and marking the initial length of a calculated section, as well as the measurement error of the tensile testing machine. These also include operator reading error, repeated relative reduction measurements, as well as the error of measuring the sample diameter by a micrometer before and after the tests. During the measurements, temperature deviation was demonstrated to constitute an additional source of uncertainty when the ambient temperature is different from the standard temperature value ((20±5)°C). Assumptions underlying laws describing the distribution of input values were assigned. Tensile tests are shown to be characterised by two components of uncertainty evaluated as types A and B. A mathematical model constructed for measuring relative elongation and relative reduction during tensile tests is presented. The standard uncertainties of input values are evaluated based on the assumed laws of their distribution. A correlation between the final length of the calculated section, the diameter of the sample following the test, and the applied force, is revealed. Expressions for the calculation of sensitivity coefficients, which characterize variations in the output value (relative elongation) depending on variations of input values, were obtained. The total and extended measurement uncertainties were evaluated. Based on the performed studies, a procedure for evaluating measurement uncertainty when carrying out tensile tests of high-strength bolts was described. The evaluation of measurement uncertainty during the product testing was shown to be a rather labourconsuming work. In this regard, the authors propose the development of procedures for evaluating the measurement uncertainty during the tests with their inclusion into regulatory documents for control methods.

Analysis and comparison of Bayesian methods for type A uncertainty evaluation with prior knowledge

If a number of observations about a certain quantity may be assumed independent, drawn from a Gaussian distribution, Supplement 1 to the GUM recommends that the standard uncertainty associated with the quantity be obtained by a formula that is applied to more than three observations. Various articles have recently appeared proposing Bayesian methods to surmount this limitation. Some of these methods, which require prior knowledge about the quantity, are reviewed in this article.

DEVELOPMENT OF ABSOLUTE MEASUREMENT SYSTEM FOR 𝑾AIR IN 60CO GAMMA RAYS.

In the ICRU Report 90, the uncertainty of the recommendation for ${{W}}_{{air}}$ was changed from 0.15 to 0.35%. The purpose of this study is to develop an absolute measurement system for ${{W}}_{{air}}$ in electrons with lower uncertainty using 60Co gamma rays. ${{W}}_{{air}}$ was determined by the ratio of the energy deposition to the number of ion pairs created in a given volume of air using a graphite calorimeter and a graphite-wall ionisation chamber. The obtained value for ${{W}}_{{air}}$ was 33.91 eV with a relative standard uncertainty of 0.08 eV (k = 1), and was in good agreement with the recommended value of the ICRU Report 90 (33.97 eV). Additionally, the uncertainty for ${{W}}_{{air}}$ obtained in this investigation is 0.23% and is comparable with that reported by Burns etal., which is the lowest uncertainty in recent studies determining ${{W}}_{{air}}$ In the future, the proposed system can be used to measure ${{W}}_{{air}}$ in high-energy electron beams.

Validating a double Gaussian source model for small proton fields in a commercial Monte-Carlo dose calculation engine

PurposeThe primary fluence of a proton pencil beam exiting the accelerator is enveloped by a region of secondaries, commonly called “spray”. Although small in magnitude, this spray may affect dose distributions in pencil beam scanning mode e.g., in the calculation of the small field output, if not modelled properly in a treatment planning system (TPS). The purpose of this study was to dosimetrically benchmark the Monte Carlo (MC) dose engine of the RayStation TPS (v.10A) in small proton fields and systematically compare single Gaussian (SG) and double Gaussian (DG) modeling of initial proton fluence providing a more accurate representation of the nozzle spray. MethodsThe initial proton fluence distribution for SG/DG beam modeling was deduced from two-dimensional measurements in air with a scintillation screen with electronic readout. The DG model was either based on direct fits of the two Gaussians to the measured profiles, or by an iterative optimization procedure, which uses the measured profiles to mimic in-air scan-field factor (SF) measurements. To validate the DG beam models SFs, i.e. relative doses to a 10 × 10 cm2 field, were measured in water for three different initial proton energies (100MeV, 160MeV, 226.7MeV) and square field sizes from 1×1cm2 to 10×10cm2 using a small field ionization chamber (IBA CC01) and an IBA ProteusPlus system (universal nozzle). Furthermore, the dose to the center of spherical target volumes (diameters: 1cm to 10cm) was determined using the same small volume ionization chamber (IC). A comprehensive uncertainty analysis was performed, including estimates of influence factors typical for small field dosimetry deduced from a simple two-dimensional analytical model of the relative fluence distribution. Measurements were compared to the predictions of the RayStation TPS. ResultsSFs deviated by more than 2% from TPS predictions in all fields <4×4cm2 with a maximum deviation of 5.8% for SG modeling. In contrast, deviations were smaller than 2% for all field-sizes and proton energies when using the directly fitted DG model. The optimized DG model performed similarly except for slightly larger deviations in the 1×1cm2 scan-fields. The uncertainty estimates showed a significant impact of pencil beam size variations (±5%) resulting in up to 5.0% standard uncertainty. The point doses within spherical irradiation volumes deviated from calculations by up to 3.3% for the SG model and 2.0% for the DG model. ConclusionProperly representing nozzle spray in RayStation’s MC-based dose engine using a DG beam model was found to reduce the deviation to measurements in small spherical targets to below 2%. A thorough uncertainty analysis shows a similar magnitude for the combined standard uncertainty of such measurements.

A reference material for evaluating full-field out-of-plane deformation measurement system

Optical techniques such as Digital Speckle Pattern Interferometry(DSPI) and Digital Image Correlation (DIC) have been widely used in deformation measurement for their advantages of full-field, non-contact and high accuracy. To exploit the advantages of those optical techniques and enhance the confidence in the data from the optical system, a physical reference material (PRM) that can generate a deformation field with submicron uncertainty is proposed. The PRM is a circular plate of composite structure including a central rod and the peripheral annular plate clamped at the edge, , the central rod of which has merely displacement and no deformation under displacement loading. The displacement of the central area of the PRM is used for calibration, which provides connection to the national standard for length. Through traceability comparison, the expanded uncertainty of full field deformation of the PRM is 0.03μm, with a coverage factor of K=2. The PRM is used to calibrate a digital speckle pattern interferometry system. The combined standard uncertainty (CSU) of the full-field out-of-plane deformation measurement is 0.090μm. Both theoretical analysis and experiments results show that the proposed device can be applied as a PRM to calibrate and evaluate optical full-field out-of-plane deformation measurement system to a submicron level of uncertainty.

Evaluation of the Influence of Machine Tools on the Accuracy of Indoor Positioning Systems

In recent years, the use of indoor localization techniques has increased significantly in a large number of areas, including industry and healthcare, primarily for monitoring and tracking reasons. From the field of radio frequency technologies, an ultra-wideband (UWB) system offers comparatively high accuracy and is therefore suitable for use cases with high precision requirements in position determination, for example for localizing an employee when interacting with a machine tool on the shopfloor. Indoor positioning systems with radio signals are influenced by environmental obstacles. Although the influence of building structures like walls and furniture was already analysed in the literature before, the influence of metal machine tools was not yet evaluated concerning the accuracy of the position determination. Accordingly, the research question for this article is defined: To what extent is the positioning accuracy of the UWB system influenced by a metal machine tool?The accuracy was measured in a test setup, which consists of a total of four scenarios in a production environment. For this purpose, the visual contact between the transmitter and the receiver modules, including the influence of further interfering factors of a commercially available indoor positioning system, was improved step by step from scenario 1 to 4. A laser tracker was used as the reference measuring device. The data was analysed based on the type A evaluation of standard uncertainty according to the guide to the expression of uncertainty in measurement (GUM). It was possible to show an improvement in standard deviation from 87.64cm±32.27cm to 6.07cm±2.24cm with confidence level 95% and thus provides conclusions about the setup of an indoor positioning system on the shopfloor.

APMP-APLAC joint proficiency testing programs for elemental analysis in food with metrological reference values: Assessment of participants' performance considering measurement uncertainties

The Asia Pacific Metrology Program (APMP) and the Asia Pacific Laboratory Accreditation Cooperation (APLAC) joint Proficiency Testing (PT) programs for toxic elements such as cadmium (Cd) and lead (Pb) or nutritional elements such as iron (Fe) and zinc (Zn) in food were organized by the Korea Research Institute of Standards and Science (KRISS) with the aim of enhancing the quality of measurement and metrological traceability in various economies of the Asia Pacific region by evaluating the performance with rigorous evaluation. Three APMP-APLAC joint PT programs for elemental analyses were carried out by KRISS sequentially, where candidate certified reference materials (CRMs) were used as the PT materials and metrologically traceable certified reference values (RVs) were used as the PT assigned values for the evaluation of participants' results, which allows reliable evaluation of participant performance. This article describes the operation of the PTs and the overall performance of the participating laboratories. The effectiveness of these joint PT programs and trends in PT performance assessment are also discussed. These PT programs confirm the significant importance of using the metrologically traceable RVs instead of the consensus values from participants as the PT assigned value for reliable assessment. The lack of understanding of the concept of coverage factor, degree of freedom, standard uncertainty, and expanded uncertainty was revealed by some participants in these PT programs. Interpreting the zeta-scores or En scores, which are derived by using measurement uncertainties, in conjunction with the z-scores is highly meaningful for assessing participants' ability in measurement capabilities and measurement uncertainty evaluation. Assessment of participants' performance considering measurement uncertainties helps the participants to check how reasonable their measurement uncertainty estimation was. The results of PTs also demonstrated that these PT programs are useful for improving the measurement capability of the laboratories, whereas more capability-building in uncertainty evaluation is required for further improvement.

Intra-GUM comparisons for the estimation of measurement uncertainty: Application to a chromatographic assay of four statins in a dry form

The chromatographic method (HPLC) is well-known for its dependability and precision in pharmaceutical analyses for assessing the quality and efficacy of drug products. However, the characteristics of the HPLC method make sense only after a careful evaluation of the measurement uncertainty. Nevertheless, it has been observed that precise identification of the sources of uncertainty resulting from the operational mode using the HPLC technique to assess their standard uncertainty based on the ISO-GUM approach is not obvious.Because of our extensive bibliographic search, we noticed that many studies published on the estimate of the uncertainty in chromatographic methods (HPLC) using the Eurachem/Citac guide are somewhat diverse in their use of this approach. The documentary research revealed four mathematical models namely, GUM1, GUM2, GUM3, and GUM4 that are most used to estimate the measurement uncertainty of the HPLC technique. Hence, a comparison between the four GUM mathematical models was carried out graphically and statistically using one-way ANOVA followed by Tuckey and Scheffe tests. The comparison results show a significant difference, which may create confusion in the reporting of measurement results as well as problems in making sound decisions. This leads to the suggestion that alternative approaches, such as the approach of a total error or ISO 11325, be used to check the ISO-GUM method's calculations of measurement uncertainty.

Signal-stabilized Al2O3:C-OSL dosimeter “checking chip” for correcting OSL reader sensitivity variation

Since an OSL reader sensitivity varies 15% over two years, the sensitivity variation should be corrected for every measurement. Conventionally, the OSL reader sensitivity is corrected by either preparing a new reference OSL dosimeter or reusing a reference OSL dosimeter previously used for calibration with corrections for signal depletion and fading effect. To facilitate the correction of the OSL reader sensitivity, a signal-stabilized Al2O3:C-OSL dosimeter “checking chip” was developed in this study. The checking chip has small signal depletion and fading effect, and can correct the OSL reader sensitivity without any corrections. The checking chip was prepared through the following steps. (a) The commercial OSL dosimeter was irradiated with approximately 100 Gy. (b) The irradiated dosimeter was partially bleached by exposing visible light at 30 s to decrease the effect of signal depletion. (c) The partially bleached dosimeter was stored at 50 °C for 30 d to stabilize signal regeneration. To evaluate the usability of the checking chip, dose measurements in a high-energy photon beam were performed for half a year. The absorbed dose to water in a high-energy photon beam was determined by the calibrated ionization chamber and the OSL dosimeter. The sensitivity variation of the OSL reader was corrected by reading the checking chip on every measurement day. The signal stability of the checking chip related to multiple readings and day elapsing were −0.013% per reading and within ±0.5% at 100 d, respectively. The relative standard uncertainty of dose determination with the OSL reader sensitivity correction was 1.7%. The OSL signal of the checking chip was sufficiently stable as a reference signal source and the OSL reader sensitivity variation can be more easily corrected by using the checking chip with the same uncertainty as the conventional method.

Note on uncertainty in Monte Carlo dose calculations and its relation to microdosimetry

PurposeThe Type A standard uncertainty in Monte Carlo (MC) dose calculations is usually determined using the “history by history” method. Its applicability is based on the assumption that the central limit theorem (CLT) can be applied such that the dispersion of repeated calculations can be modeled by a Normal distribution. The justification for this assumption, however, is not obvious. The concept of stochastic quantities used in the field of microdosimetry offers an alternative approach to assess uncertainty. This leads to a new and simple expression. MethodsThe value of the MC determined absorbed dose is considered a random variable which is comparable to the stochastic quantity specific energy, z. This quantity plays an important role in microdosimetry and in the definition of the quantity absorbed dose, D. One of the main features of z is that it is itself the product of two other random variables, specifically of the mean dose contribution in a ‘single event’ and of the mean number of such events. The term ‘single event’ signifies the sum of energies imparted by all correlated particles to the matter in a given volume. The similarity between the MC calculated absorbed dose and the specific energy is used to establish the ‘event by event’ method for the determination of the uncertainty. MC dose calculations were performed to test and compare both methods. ResultsIt is shown that the dispersion of values obtained by MC dose calculations indeed depend on the product of the mean absorbed dose per event, and the number of events. Applying methods to obtain the variance of a product of two random variables, a simple formula for the assessment of uncertainties is obtained which is slightly different from the ‘history by history’ method. Interestingly, both formulas yield indistinguishable results. This finding is attributed to the large number of histories used in MC simulations. Due to the fact that the values of a MC calculated absorbed dose are the product of two approximately Normal distributions it can be demonstrated that the resulting product is also approximately normally distributed. ConclusionsThe event by event approach appears to be more suitable than the history by history approach because it takes into account the randomness of the number of events involved in MC dose calculations. Under the condition of large numbers of histories, however, both approaches lead to the same simple expression for the determination of uncertainty in MC dose calculations. It is suggested to replace the formula currently used by the new expression. Finally, it turned out that the concept and ideas that were developed in the field of microdosimetry already 50 years ago can be usefully applied also in MC calculations.

Decadal validation of the LASP TRF cryogenic radiometer by NIST, and establishment of a replacement room temperature standard* *Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.

We present the results of a recent, extensive measurement campaign validating the traceability of the solar irradiance record and Earth radiation budget data. The campaign also established future traceability, thus ensuring confidence in the continuing climate-data record. The total solar irradiance radiometer facility (TRF) at the Laboratory for Atmospheric and Space Physics (LASP) Boulder, uses a liquid helium cooled cryogenic radiometer as the reference standard for the validation of spaceflight total solar irradiance (TSI) instrumentation. In 2008 the radiometer was directly compared to the National Institute of Standards and Technology (NIST) Primary Optical Watt Radiometer (POWR) at a wavelength of 532.12 nm. At TSI power levels, a correction factor of 1.000 306 with an associated standard uncertainty (u) of 0.000 098, was reported for the TRF radiometer scale when using external voltage measurement electronics, and not correcting for cavity heating non-equivalence or cavity absorptance. The TRF radiometer has recently been revalidated at LASP using a POWR calibrated silicon photodiode trap transfer standard named TT4. We report a correction factor of 0.999 787, u = 0.000 285 to align the TRF radiometer scale with the current NIST POWR scale. A new room temperature reference standard radiometer was established. It measured 133 parts per million (ppm) higher than POWR using the same silicon transfer standard as above, and in a separate direct measurement, 168 ppm lower than the TRF radiometer shuttered at 400 s full shutter cycle. The difference agrees within stated uncertainties. A correction of 0.999 867, u = 0.000 247 will align the new radiometer scale with the NIST radiant power scale of POWR.