Table of contents

A method is presented for evaluating the cross-spectral density diffracted by a circular aperture in the Fresnel approximation. Our proposal is a generalization to partially coherent illumination of the classical solution to the problem of near-field diffraction due to a circular aperture. We show that our generalization covers particular cases already reported in the literature and present numerical and experimental results that verify our proposal. This work is a contribution to the treatment of diffraction by multiple apertures.

The Physikalisch-Technische Bundesanstalt (PTB) has used the BESSY I 800 MeV electron storage ring as a primary source standard since 1984. The calculable spectral photon flux Φ_E of a bending magnet with relative uncertainties of 4 × 10⁻⁴ to 4 × 10⁻³ for the photon energy 1 eV to 15 keV was used in a broad spectral range from the visible to the soft X-ray range for the calibration of radiation sources and energy-dispersive X-ray detectors. In 1998, BESSY II was brought into operation. Owing to its higher electron energy, of 1.7 GeV, the useful spectral range could be extended significantly into the X-ray region up to a photon energy of about 50 keV, while special storage-ring operation at 900 MeV results in a spectrum up to about 7 keV. The PTB has established BESSY II as a European primary source standard from the visible to the X-ray range by setting up equipment for the measurement of all storage-ring parameters and geometrical quantities involved in the calculation of Φ_E according to Schwinger. At BESSY II, Φ_E from a bending magnet can be calculated with a relative standard uncertainty of 3 × 10⁻⁴ for photon energies below 3 keV, rising to 2 × 10⁻³ at 50 keV.

The undispersed synchrotron radiation from bending magnets at the primary standard source BESSY I has been used for many years for the calibration of energy-dispersive X-ray detectors. It has the advantage of continuously covering a broad spectral range from a few electronvolts up to a few kiloelectronvolts with lower uncertainty of the calculated spectral photon flux than any other source in that spectral range. With the recent establishment of BESSY II as a primary source standard, the range of radiometry is further extended into the X-ray range up to about 50 keV. In this paper we present results on the calibration of a Si(Li) detector at BESSY I and II. BESSY I was operated at a nominal electron energy of 800 MeV and BESSY II at 900 MeV and 1700 MeV. The comparison of the primary source standards BESSY I and II yielded perfect agreement. The relative uncertainty of the comparison of 0.007 is dominated by the measurement at B1. It is demonstrated that BESSY II operated at 1700 MeV electron energy is much more suitable for the calibration of energy-dispersive X-ray detectors.

We describe some new estimates concerning the recently proposed SEE (Satellite Energy Exchange) experiment for measuring the gravitational interaction parameters in space. The experiment entails precision tracking of the relative motion of two test bodies (a heavy ''Shepherd'', and a light ''Particle'') on board a drag-free space capsule. The new estimates include (i) the sensitivity of Particle trajectories and G measurement to the Shepherd quadrupole moment uncertainties; (ii) the measurement errors of G and the strength of putative Yukawa-type force whose range parameter λ may be either of the order of a few metres or close to the Earth radius; (iii) a possible effect of the Van Allen radiation belts on the SEE experiment due to test-body electric charging. The main conclusions are that (i) the SEE concept may allow G to be measured with an uncertainty of less tha 1 part in 10⁷ and progress up to two orders of magnitude is possible in the assessment of possible Yukawa forces and (ii) Van Allen charging of test bodies is a significant problem but it may be solved by existing methods.

The primary frequency standard LPTF-JPO employs a caesium thermal beam, and optical pumping techniques. We present the main parts of the design. The short-term stability is reported, σ_y(τ) = 3.5 × 10⁻¹³ τ^−1/2, where τ is the averaging time. The general expression for frequency shift for a square-wave frequency modulation is given. We discuss the determination of each frequency shift, and we present new methods to evaluate some of them. A relative combined standard uncertainty of 6.4 × 10⁻¹⁵ (1 σ) is obtained.

We develop a comprehensive approach to the evaluation of the uncertainty of a primary frequency standard. Indirect, model-dependent means are employed for the evaluation of all known biases. This approach leads to a lower combined standard uncertainty (CSU) and leaves frequency measurements under altered conditions as a powerful search technique for unknown biases. We report the results of this evaluation technique applied to NIST-7, one of the United States' primary frequency standards. The best CSU value we have reported to the Bureau International des Poids et Mesures (BIPM) is 5 × 10⁻¹⁵, while a vigorous application of this evaluation process would suggest that a limiting Type B uncertainty of 3.5 × 10⁻¹⁵ is possible. We discuss this difference and the implications of reporting optimistic values. We also discuss the history of reported evaluations of NIST-7 including those made before the full implementation of the techniques presented here.

The working equation of a capillary viscometer, used generally in the form ν = kν − B/τ (where ν is kinematic viscosity; τ is outflow time; k and B are viscometer constants), can be deduced directly from the Navier-Stokes equation. The surface tension only affects the k parameter. For a Ubbelohde-type viscometer with suspended level, the curvature of the meniscus, which compensates the influence of the mean surface tension, has been calculated. The relation often used for the capillary pressure in tubes, p_σ = 2σ/R, is only approximately valid for radii R < 0.3 mm. The Knibbs method, which uses external variable pressure, provides a means of calibrating viscometers to high accuracy using only one reference liquid.

The national metrology institutes of the United Kingdom (NPL), France (LCIE), the United States (NIST), and the Russian Federation (VNIIFTRI) have completed an international comparison of radio frequency (rf) power measurement capability in rectangular waveguide R-400 (WR-22). Each laboratory measured the effective efficiency and reflection coefficient of the same bolometric power sensors in the frequency range from 33 GHz to 50 GHz in 1 GHz steps. This paper summarizes the results of this comparison.

A high-precision comparison of dc voltages generated by a 10 GHz SINIS (superconductor/insulator/normal/insulator/superconductor) Josephson non-hysteretic junction array and a 70 GHz SIS (superconductor/insulator/superconductor) Josephson junction array is described. The paper also describes a method of minimizing the Type A measurement uncertainty. The measurements were carried out at the 10 mV level. The agreement between both output voltages was determined to 0.2 nV with a Type A uncertainty of 0.5 nV.

The results of a bilateral comparison of 10 V Josephson array voltage standards of the Ulusal Metroloji Enstitüsü (TÜBTAK-UME, Turkey) and the Bureau National de Métrologie-Laboratoire Central des Industries Électriques (BNM-LCIE, France), in the framework of EUROMET Project No. 469, are reported. A set of four Zener-diode-based voltage reference standards (Fluke 732B), delivered by the UME, was used as a transfer standard between the two laboratories. The results show an agreement within 97 nV with an overall uncertainty (1 σ) of 98 nV.