Y. Hermier

Direct Determination of the Boltzmann Constant by an Optical Method

We have recorded the Doppler profile of a well-isolated rovibrational line in the nu(2) band of (14)NH(3). Ammonia gas was placed in an absorption cell thermalized by a water-ice bath. By extrapolating to zero pressure, we have deduced the Doppler width which gives a first measurement of the Boltzmann constant k(B) by laser spectroscopy. A relative uncertainty of 2 x 10(-4) has been obtained. The present determination should be significantly improved in the near future and contribute to a new definition of the kelvin.

Isotopic and other influences on the realization of the triple point of hydrogen

Within an international collaboration of the eight metrological institutes represented by the authors, the dependence of the triple-point temperature of equilibrium hydrogen on the deuterium content at low concentrations has been precisely determined so that the uncertainty in realizing the triple point as a temperature fixed point might be reduced by nearly one order of magnitude. To investigate the thermodynamic properties of the hydrogen–deuterium mixtures and to elucidate the factors that influence the melting temperature, 28 sealed fixed-point cells have been filled and measured, and some of these have been compared with an open-cell system. Hydrogen gas with a deuterium content ranging from 27.2 µmol D/mol H to 154.9 µmol D/mol H was studied using cells containing five different types of spin-conversion catalyst, with different catalyst-to-liquid volume ratios (a few per cent to more than 100%) and of different designs. The latter consideration is especially influential in determining the thermal behaviour of the cells and, thus, the temperature-measurement errors. The cells were measured at the eight participating institutes in accordance with a detailed protocol that facilitates a direct comparison of the results. Through analysis of the measurements, significant inter-institute deviations due to different measurement facilities and methods have been ruled out with respect to the determination of both the melting temperatures and the thermal parameters of the cells. The uncertainty estimates for the determination of the deuterium content have been verified by including isotopic analysis results from four different sources. The slope of the dependence of the triple-point temperature of equilibrium hydrogen isotopic mixtures on the deuterium content has been deduced from the melting temperatures of those sample portions not in direct contact with the catalysts. Evaluation of the data using different mathematical methods has yielded an average value of 5.42 µK per µmol D/mol H, with an upper bound of the standard uncertainty of 0.31 µK per µmol D/mol H. This is close to the literature value of 5.6 µK per µmol D/mol H that was obtained at higher deuterium concentrations. (Some figures in this article are in colour only in the electronic version)

CCT-K2: key comparison of capsule-type standard platinum resistance thermometers from 13.8 K to 273.16 K

Calibrated capsule-type standard platinum resistance thermometers were used to compare national realizations of the International Temperature Scale of 1990 (ITS-90) from 13.8033 K, the triple point of equilibrium hydrogen, to 273.16 K, the triple point of water, for seven countries in CIPM Key Comparison CCT-K2. Measurements were made at temperatures close to the eight low-temperature defining fixed points of the ITS-90, using a copper comparison block capable of simultaneously holding nine thermometers. Two separate measurement runs were performed, allowing two different groups of capsules from each laboratory to be examined. The results are used to determine the degree of equivalence of the independent national realizations of the scale for use in the Mutual Recognition Arrangement Appendix B database. In addition, measurements were made with the first group of thermometers at approximately eighty temperatures throughout the cryogenic range, which provide information to evaluate some of the so-called scale non-uniqueness issues inherent in the ITS-90 interpolation scheme.

A New Generation of Multicells for Cryogenic Fixed Points at BNM/INM

In January 2000 a European Project called “MULTICELLS” started, in the field of the realisation of low‐temperature standards [1]. In the range from 14 K to 234 K, two competing designs of modular multi‐compartment cells (multicells) for the realisation of low‐temperature fixed points of the ITS‐90 were developed and fabricated by two different partners: BNM‐INM and IMGC [2]. The multicells device allows the calibration, in the same run, of up to three thermometers at all the ITS‐90 triple points in the low‐temperature range, including the mercury point. Several secondary reference points could be optionally added to the system. The limitation of the number of elements is mainly due to thermal effects (thermal homogeneity and response time) and to the dimension of the experimental space of the calorimeter used for measuring the melting curves. In order to reduce the response time, the phase‐transition interface of each element of the multicell containing the substance must be in close thermal contact with ...

Investigation of low-temperature fixed points by an international star intercomparison of sealed triple-point cells

An overview of the results of an international star intercomparison of low-temperature fixed points is given. Between 1997 and 2005, 68 sealed triple-point cells (STPCs) of the twelve laboratories represented by the authors were investigated at PTB. The STPCs are used to realize the triple points of hydrogen, neon, oxygen and argon as defining fixed points of the International Temperature Scale of 1990, ITS-90. The melting curves (MCs) of all STPCs have been measured on the same experimental equipment, adhering strictly to a single measurement program. This protocol enables separation of the effects influencing the MCs and direct comparison of the thermal behaviour of the STPCs, which are quite different with respect to design, age, gas source and filling technology. In the paper, special emphasis is given to the spread of the liquidus-point temperatures and to the uncertainty of their determination. Connections between the star intercomparison and completed and ongoing international activities are also discussed.

Isotopic effects in the neon fixed point: uncertainty of the calibration data correction

The neon triple point is one of the defining fixed points of the International Temperature Scale of 1990 (ITS-90). Although recognizing that natural neon is a mixture of isotopes, the ITS-90 definition only states that the neon should be of ?natural isotopic composition?, without any further requirements. A preliminary study in 2005 indicated that most of the observed variability in the realized neon triple point temperatures within a range of about 0.5?mK can be attributed to the variability in isotopic composition among different samples of ?natural? neon. Based on the results of an International Project (EUROMET Project No. 770), the Consultative Committee for Thermometry decided to improve the realization of the neon fixed point by assigning the ITS-90 temperature value 24.5561?K to neon with the isotopic composition recommended by IUPAC, accompanied by a quadratic equation?to take the deviations from the reference composition into account. In this paper, the uncertainties of the equation?are discussed and an uncertainty budget is presented. The resulting standard uncertainty due to the isotopic effect (k = 1) after correction of the calibration data is reduced to (4 to 40)??K when using neon of ?natural? isotopic composition or to 30??K when using 20Ne. For comparison, an uncertainty component of 0.15?mK should be included in the uncertainty budget for the neon triple point if the isotopic composition is unknown, i.e. whenever the correction cannot be applied.

An International Star Intercomparison of Low‐Temperature Fixed Points Using Sealed Triple‐Point Cells

An overview of the main results of an international star intercomparison of low‐temperature fixed points is given. Between 1997 and 2002, 52 sealed triple‐point cells (STPCs) of the thirteen laboratories represented by the authors have been investigated at PTB. The STPCs are used to realise the triple points of hydrogen, neon, oxygen, and argon, respectively, as defining fixed points of the International Temperature Scale of 1990, ITS‐90. The melting curves of all STPCs have been measured on the same experimental equipment, adhering strictly to a single measurement program. This protocol enables separation of the effects influencing the melting curves and direct comparison of the thermal behaviour of the STPCs, which are quite different with respect to design, age, gas source, and filling technology. In the paper, emphasis is given to the typical properties of the four fixed‐point substances and to the spread of the STPC parameters. Connections between the star intercomparison and completed and on‐going i...

The Comparison between a Second‐Sound Thermometer and a Melting‐Curve Thermometer from 0.8 K Down to 20 mK

BNM‐INM has realised the Provisional Low Temperature Scale of 2000 (PLTS‐2000). Additionally, for several years, the low temperature team of BNM‐INM has studied the possibility of using the properties of dilute mixtures of 3He in 4He in order to develop a local temperature scale. The team made the choice to develop a new type of thermometer based on the propagation of sound in dilute solutions of 3He in superfluid 4He, a second‐sound thermometer. For low temperatures, the properties of low concentrations of 3He in superfluid 4He are those of a nearly ideal Fermi gas. The experiments of Greywall and Owers‐Bradley et al. have shown that the velocity of second sound in 3He‐4He mixtures is very sensitive to temperature, especially below 0.6 K. In the second‐sound thermometer developed by BNM‐INM, the speed of sound is determined from the resonance spectra of an acoustic cavity. The temperature is deduced from the measurement of the resonance frequencies, by using a physical model describing the relation betwe...

A European ultralow temperature scale

Abstract A collaborative research project, supported by the Standards, Measurement and Testing programme of the European Union, has been undertaken to standardise sub-kelvin temperature measurements across European national measurement institutes. Traceability to the resulting European ULT scale has been enhanced by the development of a new prototype superconducting reference device. New glass capacitance thermometers for measurements in high magnetic fields have also been characterised. The main results of the project are presented.

CCT-K2.4: NRC/INTiBS/LNE-Cnam trilateral comparison of capsule-type standard platinum resistance thermometers from 13.8 K to 273.16 K

A trilateral comparison of capsule-type standard platinum resistance thermometers (CSPRT) was carried out between NRC (Canada), INTiBS (Poland) and LNE (France) in 2006 over the temperature range 13.8 K to 273.16 K. The NRC/INTiBS comparison made it possible to link the INTiBS realization of the International Temperature Scale of 1990 to the results of the Consultative Committee for Thermometry Key Comparison CCT-K2 over this temperature range. It revealed that calibrations at INTiBS were in agreement with the key comparison reference values of CCT-K2 within the expanded uncertainties for all temperatures of the comparison based on the data obtained with one of CSPRTs, the other CSPRT of the comparison being considered as anomalous. The linkage to the CCT-K2 data supports the inclusion of the INTiBS CMCs in the BIPM key comparison database (KCDB) and also supplies evidence to support the revision of the uncertainties of the LNE CMCs in the KCDB at the triple points of neon and hydrogen. 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 CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).