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Simonds, Brian. J. Wang, Yicheng. Zimmerman, N. M. (ELECTRONICS AND ELECTRICAL ENGINEERING LABORATORY - 817)
An Upper Bound to the Frequency Dependence of the Cryogenic Vacuum-Gap Capacitor
Metrologia - September 01, 2006

In attempting to develop a capacitance standard based on the charge of the electron, one question which has been open for many years is the frequency dependence of the vacuum-gap cryogenic capacitor. In this paper, we succeed in putting an upper bound on that frequency dependence from 0.01 Hz to 1 kHz of about 2x10-7. We do this by considering a model for the dispersionin the surface insulating films on the surface of the Cu electrodes; the crucial prediction of this model is that the dispersion falls to very low values at low temperatures. By measuring the frequency dependence over a restricted range of frequencies, we have verified this prediction, and thus provide adequate support to conclude that the model is correct. We also point out that, independent of the capacitance standard, this cryogenic capacitor provides a frequency-independent standard for measurements in fields such as the low-temperature dynamics of amorphous materials.
Keywords: capacitance standard , cryogenic , dispersion , frequency dependence
Availability information updated on September 14, 2006.
Direct ordering of this outside publication may only be available to NIST Staff

Meyer, C. W. Ripple, D. C. (PROCESS MEASUREMENTS DIVISION - 836)
Determination of SPRT Realization Uncertainties Between Points
Metrologia - September 01, 2006

Calibrated Standard Platinum Resistance Thermometers (SPRTs) are used to realize the International Temperature Scale of 1990 (ITS-90) from 13.8033 K to 1234.93 K. The SPRTs are calibrated at a series of fixed points, each assigned a temperature on the ITS‑90, by measuring the ratios of the SPRT resistances at those temperatures to that at the triple point of water (TPW).  For realizing the scale with a calibrated SPRT, a user measures the resistance ratio at the unknown temperature and uses ITS-90-defined equations to interpolate between fixed points. The uncertainty of the SPRT temperature is therefore largely influenced by the propagation of fixed-point resistance-ratio uncertainties.  For properly calculating the total SPRT temperature uncertainty, correlations of uncertainty components must be considered, in particular those involving measurement of the TPW resistance. The calculation method depends on three uncertainty-correlation-related factors involving SPRT use and calibration. The different combinations of these factors result in six different methods for calculating the realization uncertainty. This paper presents these six methods, specifies the conditions of their use, and discusses the relevant uncertainty components for each of them. It also compares the results of these methods with those of two approximations that may be used for calculating the uncertainty and explains the conditions under which the approximations agree with the proper calculations.
Keywords: ITS-90 , Platinum ResistanceThermometry , uncertainty , Temperature Scale Realization
Total pages: 14. Availability information updated on September 14, 2006.
Direct ordering of this outside publication may only be available to NIST Staff

Meyer, C. W. Tew, W. L. (PROCESS MEASUREMENTS DIVISION - 836)
ITS-90 Non-Uniqueness From PRT Subrange Inconsistencies Over the Range 24.56 K to 273.16 K
Metrologia - September 01, 2006

Calculations have been performed to study ITS-90 non-uniqueness over the range 24.5561 K to 273.16 K, where the scale is defined by an interpolating platinum resistance thermometer (PRT) that is calibrated via sets of defined fixed points. Over this range, the definition allows for the PRT to be calibrated over any of four different subranges. Each subrange has its own functional form for interpolation and its own set of calibration fixed points, and all subranges yield calibrations with equally valid realizations of the scale. Because the interpolations for the different subranges are not identical, temperature realizations from a PRT resistance measurement do not result in the same values of the ITS-90 temperature T90 when using calibrations from different subranges; these subrange inconsistencies yield non-uniqueness of the scale in the regions between fixed points. For this work, subrange inconsistency calculations have been performed on eighteen PRTs; fourteen are standard PRTs and four are miniature PRTs. The inconsistency uncertainties, which result from propagation of fixed-point uncertainties, have also been calculated. Statistics on the inconsistencies have been performed for the purpose of helping estimate an uncertainty component to T90 due to the inconsistencies. The calculations show that PRT subrange inconsistencies in the temperature region studied can be as large as 1 mK. Over small temperature ranges in this region, the inconsistencies can result in T90 uncertainties that dominate those propagated from fixed-point uncertainties. We have also studied possible correlations between PRT subrange inconsistencies and other PRT properties/parameters that are simpler to determine; these studies show that there is a correlation
Keywords: ITS-90 , temperature scale , platinum resistance thermometry , uncertainty , non-uniqueness , subrange inconsistency
Total pages: 12. Availability information updated on September 14, 2006.
Direct ordering of this outside publication may only be available to NIST Staff

Yates, Jesse. K. Amis, E. J. Barnes, Susan. E. Beers, Kathryn. L. Cygan, Zuzanna. T. (POLYMERS DIVISION - 854)
Raman Spectroscopic Monitoring of Droplet Polymerization in a Microfluidic Device
The Analyst - September 01, 2006

Thiolene based microfluidic devices were used to generate droplets of benzyl methacrylate monomer and hexanediol dimethacrylate crosslinker mixtures suspended in a water/surfactant continuous phase. A gradient of droplet composition was established and the ensemble of droplets was collected on the device. On-chip Raman spectroscopy was used to verify a composition gradient from 18 to 98 volume % benzyl methacrylate. The droplets were then exposed to UV light to initiate polymerization and subsequent Raman spectra were taken to determine extent of conversion. Conversion was found to vary with composition across the gradient with 78% conversion at low benzyl methacrylate concentrations to 95% at high benzyl methacrylate concentrations. Image analyses of micrographs taken before and after polymerization were used to measure shrinkage due to polymerization. Shrinkage values ranged from 4% to 12% and increased with increasing benzyl methacrylate concentration.
Keywords:
Total pages: 7. Availability information updated on September 14, 2006.
Direct ordering of this outside publication may only be available to NIST Staff

Reader, J. Sansonetti, C. J. (ATOMIC PHYSICS DIVISION - 842)
Spectral Radiance of Strong Lines in Positive Column Mercury Discharges With Argon Carrier Gas
Journal of Physics D: Applied Physics - September 01, 2006

The spectral radiance of the 185-nm and 254-nm lines in two positive column mercury discharge lamps was measured over a wide range of operating conditions. The lamps had internal diameters of 5 and 23 mm. Argon was used as a carrier gas. The lamps were operated with cold-spot temperatures of 20 ºC, 40 ºC, and 60 ºC. At each of these temperatures, results were obtained for five currents ranging from 20 mA to 100 mA for the 5-mm lamp and from 200 mA to 1000 mA for the 23-mm lamp. For each current studied, results were determined for argon pressures ranging from 66.6 to 666 Pa (0.5 to 5.0 Torr) in the 5-mm lamp and 26.6 to 666 Pa (0.2 to 5.0 Torr) in the 23-mm lamp . An argon miniarc was used as the radiometric standard. By calibrating the spectral response of the optical system with a well-characterized mercury pencil lamp, results were obtained for twelve additional Hg lines from 289 to 579 nm. For the 23 mm lamp the electric field in the positive column was measured. For this lamp radiated power as a percentage of input power was also determined. The results provide an experimental basis for validating computer models of Hg fluorescent lamp discharges.
Keywords: fluorescent lamp , mercury , positive column discharge , radiometry , spectral radiance
Total pages: 17. Availability information updated on September 14, 2006.
Direct ordering of this outside publication may only be available to NIST Staff