A. Peruzzi

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.

Accurate experimental determination of the isotope effects on the triple point temperature of water. I. Dependence on the 2H abundance

Variation in the isotopic composition of water is one of the major contributors to uncertainty in the realization of the triple point of water (TPW). Although the dependence of the TPW on the isotopic composition of the water has been known for years, there is still a lack of a detailed and accurate experimental determination of the values for the correction constants. This paper is the first of two articles (Part I and Part II) that address quantification of isotope abundance effects on the triple point temperature of water. In this paper, we describe our experimental assessment of the 2H isotope effect. We manufactured five triple point cells with prepared water mixtures with a range of 2H isotopic abundances encompassing widely the natural abundance range, while the 18O and 17O isotopic abundance were kept approximately constant and the 18O − 17O ratio was close to the Meijer–Li relationship for natural waters. The selected range of 2H isotopic abundances led to cells that realised TPW temperatures between approximately −140 μK to +2500 μK with respect to the TPW temperature as realized by VSMOW (Vienna Standard Mean Ocean Water). Our experiment led to determination of the value for the δ2H correction parameter of A2H = 673 μK / (‰ deviation of δ2H from VSMOW) with a combined uncertainty of 4 μK (k = 1, or 1σ).

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.

Accurate experimental determination of the isotope effects on the triple point temperature of water. II. Combined dependence on the 18O and 17O abundances

This paper is the second of two articles on the quantification of isotope effects on the triple point temperature of water. In this second article, we address the combined effects of 18O and 17O isotopes. We manufactured five triple point cells with waters with 18O and 17O abundances exceeding widely the natural abundance range while maintaining their natural 18O/17O relationship. The 2H isotopic abundance was kept close to that of VSMOW (Vienna Standard Mean Ocean Water). These cells realized triple point temperatures ranging between −220 μK to 1420 μK with respect to the temperature realized by a triple point cell filled with VSMOW. Our experiment allowed us to determine an accurate and reliable value for the newly defined combined 18, 17O correction parameter of AO = 630 μK with a combined uncertainty of 10 μK. To apply this correction, only the 18O abundance of the TPW needs to be known (and the water needs to be of natural origin). Using the results of our two articles, we recommend a correction equation along with the coefficient values for isotopic compositions differing from that of VSMOW and compare the effect of this new equation on a number of triple point cells from the literature and from our own institute. Using our correction equation, the uncertainty in the isotope correction for triple point cell waters used around the world will be <1 μK.

Dilution of impurities in water triple point cells

Controlled amounts of Si and Na impurities (0.1 to 0.5 μmol⋅mol−1 of Si and 0.2 to 1 μmol⋅mol−1 of Na) were diluted in the high-purity water of triple point of water (TPW) cells before sealing the cells. Water samples drawn from the manufactured doped cells were analyzed with high-resolution Inductively Coupled Plasma - Mass Spectrometry (ICP-MS). The TPW temperature of one of the doped cells (the cell that showed a good agreement between the nominal Si and Na amounts and the Si and Na amounts measured by ICP-MS) was measured for different water/ice relative contents. The observed TPW depression was compared to 1) the TPW depression expected from the nominal doping and 2) the TPW depression expected from the total impurity content measured by ICP-MS.

4He interpolating constant-volume gas thermometry in the range 3.0?K to 24.5561?K

The range 3.0 K to 24.5561 K of the International Temperature Scale of 1990 (ITS-90) was realized at VSL with a 4He interpolating constant-volume gas thermometer (ICVGT). The standard uncertainty of the generated scale ranged from 0.32 mK at 3.3 K to 0.38 mK at 24.5561 K. The ICVGT scale was compared with the classical absolute gas thermometer scales of the National Physical Laboratory (NPL-75, 1975) and the Kamerlingh Onnes Laboratory (KOL, 1986) and was found to deviate from them by a maximum of 1.5 mK. The non-uniqueness of the generated scale was investigated by comparing it with alternative ICVGT scales (but having equal status because still satisfying all the requirements of the ITS-90) obtained from different choices of the lowest calibration temperature and interpolation function. The size of correction effects such as thermo-molecular pressure, aerostatic head pressure and dead volume was calculated and the effectiveness of the ICVGT calibration procedure in compensating for such correction effects was evaluated.

European Dissemination of the Ultra-low Temperature Scale, PLTS-2000

The first phase of the EU collaborative project on sub‐kelvin thermometry, ‘ULT Dissemination’, is nearing completion, leading to the development of several thermometers and devices, and the instrumentation needed to disseminate the new Provisional Low Temperature Scale, PLTS‐2000, to users. Principal among these are a current‐sensing noise thermometer (CSNT), a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second‐sound acoustic thermometer and a superconductive reference device SRD‐1000. Several partners have set up 3He melting‐pressure thermometers to realise the PLTS‐2000, and will check it using Pt‐NMR, CMN and other thermometers. The scale, which was formally adopted by the Comite International des Poids et Mesures in October 2000, covers the range of temperature from 1 K down to 0.9 mK, and is defined by an equation for the melting pressure of 3He. The SRD employs novel fabrication and detection techniques with up to 10 samples, and is expected to meet the requirement...

First Prototypes of the Superconductive Reference Device SRD1000

In the framework of the European Project “Ultra‐Low Temperature Dissemination (ULT),” a superconductive reference device (SRD1000) and dedicated external measurement electronics were developed to provide direct traceability to the new Provisional Low Temperature Scale (PLTS‐2000). The SRD1000 includes 10 reference points in the temperature range 15 mK to 1 K: W (TC = 15 mK), Be (TC = 23 mK), Ir80Rh20 (TC ≈ 35 mK), Ir92Rh08 (TC ≈ 65 mK), Ir (TC = 100 mK), AuAl2 (TC = 160 mK), AuIn2 (TC = 208 mK), Cd (TC = 520 mK), Zn (TC = 850 mK) and Al (TC = 1180 mK). After extensive research and development in the preparation and in the ultra‐low temperature characterization of superconductive reference materials during the past years, eventually a final selection of the materials to be included in the first SRD1000 prototype sensors was made. In this paper, the superconducting transitions observed for the selected materials and the sample preparations are reported, the SRD1000 sensor and external electronics technology...

EU dissemination of the provisional ultra-low-temperature scale, PLTS-2000

Following the introduction of the provisional low-temperature scale from 0.9 mK to 1K, PLTS-2000, there is a need for primary and secondary thermometers and fixed points, which can disseminate the scale to users. This paper reports on the progress, within the EU collaborative project ‘ULT Dissemination’, in the development and evaluation of several devices with associated instrumentation. Principal among them are a current-sensing noise thermometer, a CMN thermometer adapted for industrial use, a Coulomb blockade thermometer, a second-sound thermometer, a 3He melting pressure thermometer for a direct realisation of the PLTS-2000. A superconductive reference device has also been developed, as a replacement for the NBS SRM-768 which is no longer available.