Using inelastic neutron scattering, the frequency – wave vector dispersion relations for the lattice vibrations in a single crystal of palladium have been determined at 120, 296, 673, and 853 °K. Analyses of the results have given force-constant models from which frequency distributions have been computed. First-neighbor interactions are dominant, but weaker interactions also exist, extending beyond sixth-nearest neighbors. The total lattice specific heat (harmonic plus anharmonic) at constant pressure has been calculated, using the frequency distribution at 296 °K and the shifts in the frequencies with changing temperature. Similar calculations were also carried out for copper, using the room temperature distribution reported by Svensson et al.; the temperature dependence of the frequencies was established by carrying out measurements along major symmetry directions of Cu at 296, 473, and 673 °K. The electronic specific heats of Cu and Pd have been calculated at temperatures between 0 and 900 °K. The electronic specific heat of Cu agrees well enough with the linear relation Ce = γT for T < 700 °K. For Pd, Ce is anomalously high at low temperatures, in agreement with experiments at helium temperature, but tends to saturate for temperatures > 200 °K.

The dispersion relations in platinum have been measured at 90 °K by the inelastic scattering of thermal neutrons. Born–von Kármán models of the force system have been calculated by fitting to the dispersion curves. Fourth-neighbor forces, with weaker interactions probably extending to at least sixth neighbors, are required to fit the data. A frequency distribution has been calculated from the force constants of the most realistic model.Some measurements are also reported of frequencies at a temperature of 473 °K. The mean frequency shift from 90 to 473 °K was found to be −2.0%.In the [0ζζ]T1 branch, anomalous behavior, similar to that observed in palladium, has been studied at temperatures of 90, 296, and 473 °K. As in Pd, the anomaly in Pt is markedly broadened and weakened with increasing temperature. The phonon wave vectors corresponding to possible Kohn transitions in the (001) plane have been determined by machine calculation, using Fermi surfaces given in the literature. These results strongly suggest that the anomaly along the T1 branch arises largely from transitions across the "heavy" hole Fermi sheet formed from the fifth-band electrons. A comparison is made with similar results for palladium and nickel.

A key comparison of low absolute pressure standards, organized under the auspices of the Consultative Committee for Mass and Related Quantities (CCM), was carried out at seven national metrology institutes (NMIs) between March 1998 and September 1999 in order to determine the degrees of equivalence of the standards at pressures in the range 1 Pa to 1000 Pa. The primary standards, which represent two principal measurement methods, included five liquid-column manometers and four static expansion systems. The transfer standard package consisted of four high-precision pressure transducers: two capacitance diaphragm gauges to provide high resolution at low pressures, and two resonant silicon gauges to provide the required calibration stability. Two nominally identical transfer packages were used to reduce the time required for the measurements, with Package A being circulated among laboratories in the European region (Istituto di

NIST has characterized two large diameter (35.8 mm) piston/cylinder assemblies as primary pressure standards in the range 0.05 MPa to 1.0 MPa with uncertainties approaching the best mercury manometers. The realizations of the artefacts as primary standards are based on the dimensional characterization of the piston and cylinder, and models of the normal and shear forces on the base and flanks of the piston. We have studied two piston/cylinder assemblies, known at the National Institute of Standards and Technology (NIST) as PG 38 and PG 39, using these methods. The piston and cylinder of both assemblies were accurately dimensioned by Physikalisch Technische Bundesanstalt (PTB). All artefacts appeared to be round within ±30 nm and straight within ±100 nm over a substantial fraction of their heights. PG 39 was dimensioned a second time by PTB, three years after the initial measurement, and showed no significant change in dimensions or effective area. Comparisons of the effective area of PG 38 and PG 39 from dimensional measurements, against those obtained with calibration against the NIST ultrasonic interferometer manometer (UIM), are in agreement within the combined standard (k = 1) uncertainty of the dimensional measurements and the UIM. A cross-float comparison of PG 38 versus PG 39 also agreed with the dimensional characterization within their combined standard uncertainties and with the UIM calibrations. The expanded (k = 2) relative uncertainty of the effective area is about 6.0 × 10 −6 for both assemblies.

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