In the last 30 days

• Open/close Radionuclide activity measurements in environmental samples of water, soil and grass: CCRI(II)-S4 comparison report

  A Shakhashiro and U Sansone  2009 Metrologia 46 06004 Tag this article

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  In the frame of the Mutual Recognition Arrangement of the International Committee for Weights and Measures, the Consultative Committee for Ionizing Radiation Section II—Measurement of Radionuclides—proposed to the national metrology institutes of Member States signatories of the Metre Convention, to participate in an interlaboratory comparison exercise on the determination of gamma emitting radionuclides in soil, grass and water. The exercise was piloted by the Reference Materials Group at the IAEA's Laboratories in Seibersdorf (Austria).

  The exercise is classed as a supplementary comparison, with reference CCRI(II)-S4 and the present report will be referenced in the Bureau International des Poids et Mesures (BIPM) key comparison database (KCDB).

  Five national metrology institutes took part in the present interlaboratory comparison exercise: the Czech Metrology Institute, the National Centre of Metrology, Bulgaria, National Institute of Standards and Technology, USA, the National Physical Laboratory, UK, and Physikalisch-Technische Bundesanstalt, Germany. In addition, two expert laboratories participated in this comparison: the Japan Chemical Analysis Centre, Japan, and the IAEA Chemistry Unit of the Physics, Chemistry and Instrumentation Laboratory in Seibersdorf, Austria.

  This comparison was aimed at:

  • supporting calibration and measurement capability (CMC) claims of national metrology institutes for radionuclide measurements in different matrices (grass, soil and water), and
  • assigning the certified reference value of the 372 grass Certified Reference Material.

  This report presents the sample preparation methodology, participants' results and data comparison approach.
  
  

  Appendix I contains the analytical results sorted according to the analyte with the Mixture Models Median (MM-median) graphs.

  Appendix II reports tables of results evaluation, including uncertainty budgets sorted by institute.

  Appendix III contains the documentation used in this comparison.

  The comparison study materials were prepared and distributed to the participating laboratories in June 2006. The deadline for receiving the results from the participants was set at 15 September 2006. The participating laboratories were requested to analyse the samples employing the methods used in their routine work.

  The comparison results have demonstrated that in the case of ⁴⁰K, ⁵⁴Mn, ⁶⁰Co, ⁶⁵Zn, ¹³⁴Cs, ¹³⁷Cs and ²⁴¹Am the participating institutes could produce reliable and comparable analytical results of the highest metrological traceability within ±10% for soil, water and grass samples. However, ¹⁰⁹Cd was the most problematic nuclide.

  It was found that there is a need for corrective action to improve the methodology of correction for matrix effect in the case of this nuclide in a mineral matrix, where a complex interference is present.

  The analytical uncertainties associated with the results were, in general, appropriate for the analytes and matrices considered in the current comparison.

  Main text. 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 kcdb.bipm.org/.

  The final report has been peer-reviewed and approved for publication by the CCRI Section II, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

• Open/close Evolution of the 'Guide to the Expression of Uncertainty in Measurement'

  Walter Bich et al  2006 Metrologia 43 S161 Tag this article

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  A number of Joint Committees of the Bureau International des Poids et Mesures and other international organizations carry out particular tasks of common interest. The Joint Committee for Guides in Metrology (JCGM) has amongst its tasks the promotion of the ' Guide to the Expression of Uncertainty in Measurement' (GUM), the preparation of further documents for its broad application, and revision and promotion of the use of the ' International Vocabulary of Basic and General Terms in Metrology'. This paper summarizes the documents relating to the GUM planned by JCGM.

• Open/close The Refractive Index of Air

  Bengt Edlén  1966 Metrologia 2 71 Tag this article

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  Present knowledge of the refractive index of air is reviewed. Regarding the absolute values there are as yet no definite indications that the standard adopted in 1953 on the basis of Barrell and Sears' measurements should be changed, but new experiments aiming at reducing the present uncertainty of about ± 5 × 10 ^-8 would be desirable.

  Several recent investigations have contributed important new information on the dispersion of air, which has made it possible to derive an improved dispersion formula for standard air, ( n − 1) _s × 10 ⁸ = 8342.13 + 2406030 (130 − σ ²) ^-1 + 15997 (38.9 − σ ²) ⁻¹, where σ is the vacuum wave-number in μm ^-1. The deviations from the 1953 formula are small and practically negligible in most spectroscopic work.

  An equation for the dependence of refractivity on temperature and pressure based on theoretical considerations has been derived. For the range of atmospheric conditions normally found in a laboratory the equation can be approximated by the formula ( n − 1) _tp = ( n − 1) _s × 0.00138823 p/(1 + 0.003671 t), with p in torr, t in °C, and ( n − 1) _s given by the dispersion formula for standard air.

  The effect of carbon dioxide and water vapour is discussed. From Erickson's dispersion data for water vapour, combined with Barrell and Sears' absolute measurements, one obtains the equation n _tpf – n _tp = −f (5.722 − 0.0457 σ ²) × 10 ^-8 for the difference in refractive index of moist air, containing f torr of water vapour, and dry air at equal temperature and total pressure. The equation is valid for visible radiations and normal atmospheric conditions.

• Open/close On the validity of methods of uncertainty evaluation

  R Willink  2010 Metrologia 47 80 Tag this article

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  This paper continues a discussion generated by a recent paper of Hall ( 2008 Metrologia 45 L5–8) regarding the performance of methods of uncertainty evaluation. The 'validity' of a method of generating intervals of measurement uncertainty is identified principally with the frequency with which these intervals contain the measurand. Two approaches to the evaluation of such intervals are described, and their performances are compared for the simple measurement function appearing in Hall's paper. The first is a Bayesian approach, which is consistent with the numerical method described in Supplement 1 to the Guide to the Expression of Uncertainty in Measurement. The second is an approach based on frequentist principles. Simulations with fixed values of the unknown parameters are conducted to find the rate at which the methods generate intervals containing the value of the measurand and to find the mean widths of the intervals produced. The results show that the standard Bayesian procedure and its modifications can perform poorly. In contrast, the frequentist procedure achieves the required rate of 0.95 while generating intervals of similar width.

• Open/close Uncertainty evaluation for measurement of LED colour by Monte Carlo simulations

  N Pousset et al  2009 Metrologia 46 704 Tag this article

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  A measurement bench for colorimetric parameters (chromaticity coordinates, correlated colour temperature and colour rendering indices) of LED lightings is described. The analysis of uncertainty sources on relative spectral measurements is exposed. Calculation results of uncertainties, by Monte Carlo simulations, for spectral measurements as well as colorimetric parameters are presented.

• Open/close Long-term comparison of caesium fountain primary frequency standards

  Thomas E Parker  2010 Metrologia 47 1 Tag this article

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  There are currently nine caesium fountain primary frequency standards regularly reporting calibrations of International Atomic Time to the Bureau International des Poids et Measures (BIPM). An investigation has been carried out using data from the BIPM publication Circular T to evaluate the frequency differences among these standards and to determine whether these offsets are consistent with the stated uncertainties. The fractional frequency uncertainties of some Cs fountains are now in the range of 4 × 10 ⁻¹⁶ to 5 × 10 ⁻¹⁶. The results of this investigation show that the standards agree well with each other. An overall estimate of the caesium frequency is made using the weighted mean of all the fountains.

• Open/close High-precision gravity measurements using atom interferometry

  A Peters et al  2001 Metrologia 38 25 Tag this article

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  We have built an atom interferometer that can measure g, the local acceleration due to gravity, with a resolution of Δ g/ g = 2 × 10 ⁻⁸ after a single 1.3 s measurement cycle, 3 × 10 ⁻⁹ after 1 min and 1 × 10 ⁻¹⁰ after two days of integration time. The difference between our value for g and one obtained by a falling corner-cube optical interferometer is (7 ± 7) × 10 ⁻⁹ g. The atom interferometer uses velocity-selective stimulated Raman transitions and laser-cooled caesium atoms in an atomic fountain. We extend previous methods of analysing the interferometer to include the effects of a gravitational gradient. We also present detailed experimental and theoretical studies of potential systematic errors and noise sources.

• Open/close An Updated Edlén Equation for the Refractive Index of Air

  K P Birch and M J Downs  1993 Metrologia 30 155 Tag this article

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  The Edlén equation for the refractive index of air, published in 1966, is still widely used. Subsequent to its formulation, however, improved data have become available on the density of air and the refractivity of water vapour. The practical temperature scale has also been revised and the carbon dioxide content of normal laboratory air has increased. These effects result in a discrepancy of typically 1 × 10 ^-7. The consequent revision of the equation brings the agreement between calculation and experiment within an experimental uncertainty of ± 3 × 10 ^-8.

• Open/close Recommended table for the density of water between 0 °C and 40 °C based on recent experimental reports

  M Tanaka et al  2001 Metrologia 38 301 Tag this article

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  Experimental results from four recent research reports on the determination of the density/temperature relationship of Standard Mean Ocean Water (SMOW) under a pressure of 101 325 Pa are analysed and a new formula is recommended for metrological applications. This paper determines the formulae of density and relative density, with their uncertainties, in the temperature range 0 °C to 40 °C. The uncertainty estimation of one of the reports included in the analysis has been re-evaluated. Effects on water density due to isotopic mixtures other than SMOW, ambient pressures different from 101 325 Pa, and the presence of dissolved air, are also reviewed.

• Open/close Calculable blackbody radiation as a source for the determination of the spectral responsivity of THz detectors

  B Gutschwager et al  2009 Metrologia 46 S165 Tag this article

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  The spectral responsivity of the detector is important for the layout and quantitative interpretation of spectroscopic experiments. In the terahertz (THz) spectral range the knowledge of the total (integral) responsivity of a detector, as well as its spectral distribution, is often insufficient. PTB determined the spectral irradiance responsivity of two THz detectors, a pyroelectric DLATGS detector working at room temperature and a silicon-composite bolometer working at 4 K, in the wavelength range from 62 µm (4.82 THz) to 1340 µm (0.22 THz) with temperature radiation from blackbody radiators. Our approach is to use two THz cavity radiators in combination with THz bandpass filters to provide calculable spectral irradiances, according to Planck's law of radiation, at several wavelength bands in the THz spectral range. One cavity radiator is working at an adjustable fixed temperature in the range from 15 °C to 90 °C while the other cavity radiator operates at LN ₂ temperature. The radiation of the two cavity radiators is alternately imaged on the detector via a gold-coated chopper wheel. Hereby the background radiation is cancelled and also the necessary modulation for the lock-in detection is provided. The cavity of the high temperature radiator is coated with a dedicated paint providing high wall emissivity in the FIR and THz spectral range to ensure true blackbody behaviour of the radiator. The bottom of the low temperature radiator consists of THz absorber foam providing hereby also nearly blackbody behaviour. All individual filters and, additionally, the employed filter combinations are characterized for their transmittance in the entire wavelength range from 0.8 µm to 1700 µm to obtain a precise knowledge of the transmitted blackbody spectrum. The very reproducible results indicate that this setup allows a fast, simple and reliable determination of the spectral responsivity of THz detectors. In a next step, the uncertainty of this technique will be further evaluated and investigations will be extended to other types of detectors (e.g. LiTaO ₃ detectors and Golay cells).