Determination of an accurate Ttp vs x(isotopic) relationship for neon
Project Description
The recent isotopic composition measurements made by IRMM (the EU JRC in Geel), showed a dispersion of the composition values –and their asymmetric position with respect to “natural” neon– to such an extent that existing neon triple points realizations as ITS-90 fixed point (CNR-IMGC, INM-BNM, NRC, NPL, PTB) varies by more than 0,2 mK due only to this reason. This in much larger than the expected reduced uncertainty of the triple points realizations of the new generations of fixed points of the ITS-90 in the cryogenic range.The Project aims at making a comprehensive study on the problem, by realising the neon triple point in sealed cells or in open cells, and using neon gas bottles not included in the ones already analysed by IRMM, which will be analysed subsequently. First, a measurement recollection of previous cells will be done, including the 1978-84 CCT Comparison, the KC2, and the more recent PTB star inter-comparison. Every NMi is encouraged to review its own data on neon: IMGC will do this on its numerous sealed cells. New measurements are aimed, having a total uncertainty budget of 0,1 mK or better. Considering that Project MULTICELLS is now completed, IMGC will take charge of most of these measurements, in co-operation with INTiBS. However, as done for hydrogen, every NMI wishing to contribute with its own measurements is welcome: this is indispensible for open-cell realisations. IMGC will also take charge to keep the contacts with IRMM for organising a new batch of isotopic measurements there.The final aim is, as for hydrogen, to obtain the most accurate relationship between Ttp and isotopic composition, in order to publish it as the basis for amending in future the ITS90 also in respect to neon. The Project program will be fully defined in the first two months since its start and is expected to last two years.
Also the University of Tokyo is participating from 2010, making isotopic-composition assays on samples of natural neon.
NIST is willing to participate. The project is expected to further extend to participants outside the EU.
Progress Report 2012-04-11
A) Phase I - Recollection of neon sources commonly available to the metrologists
B) Phase II - Analytical determination of Neon isotope amount ratios with corresponding Ttp
i) Isotope measurements; ii) New Ttp determinations; iii) Definition of Ttp
Activities under i)- In 2011 more isotopic assays have been performed by KRISS. In addition KRISS prepared three artificial mixtures with different 22Ne content in 20Ne to check for the ideality of the mixtures, and by the Japanese laboratory on samples of natural neon. INRIM, NMIJ have performed more thermal measurements. Specifically, INRIM has performed measurements on the artificial mixtures, which confirmed the theoretical prediction of a quadratic component to the liquidus line.A final paper with the ultimate results and two sets of correction equations for isotopic composition, with different approaches for taking into account the presence of 21Ne, was presented at the decadal congress "Temperature, Its Measurement and Control in Science and Industry" of March 19-23, 2012, held in Los Angeles. Both equations agree to within 4 µK over the composition range of natural neon. A comprehensive Report with all the collected data from all participants will be later published in 2012 as a separate volume.
Activities under iii)- The final document is in preparation for the 2012 CCT meeting.
The Project is planned to close in 2012.
Progress Report 2009-04-02
The project was initially organised in 2004, then adjourned in 2007, in two phases:
A) Phase I - Recollection of neon sources commonly available to the metrologists
The working steps were the following: 1) make a list of commercial gas suppliers around the world; 2) reduce this list to the independent sources, based on the info from the Companies; 3) obtain from the Companies information about the origin of the neon and about the isotopic composition - and their analytical facilities; 4) try to get samples free of charge (typically 10 L in a high purity cylinder, possibly provided, even temporarily, by the supplier and foreseen of a suitable manometer) with all their specific analytical data (chemical impurities - possibly specific, not only batch, - isotopic composition), for most of them and for all typical total chemical impurity levels (from 4N to 6N ); 5) obtain information about neon from other communities potentially interested in neon isotopic compositions; 6) look for analytical means enlarging the number of available facilities able to provide neon isotopic composition with the accuracy we need. It was quite difficult to get relevant information from the producers: all declared so far distillating neon from air. INRIM, as a new member of IIF/IIR Committee A2 since 2005, is having stricter contacts with worldwide gas producers.
Additionally, in 2008 INRIM bought a stock of the purest available 22Ne and 20Ne from two different producers. Also IRMM bought some pure neon isotopes in view of work to be performed under phase II.
B) Physe II - Analytical determination of Neon isotope amount ratios with corresponding Ttp
i) Isotope measurements; ii) New Ttp determinations; iii) Definition of Ttp
Activities under i and ii) - In 2005, a basic paper has been published in the Journal Analytical Chemistry with the 2003 data, found quite unusual and requiring further studies. During 2006, more neon samples have been analysed by IRMM, basically confirming and even increasing the 2005 spread of composition. A re-compilation has been performed of the measurements on neon samples for which thermal results are known from different sources, namely the PTB Star Comparison (Euromet Project 377), showing a much lower uncertainty than CCT KC2. A progress paper presented at TEMPMEKO 2007 was published in early 2008 on Int. J. Thermophysics.
IRMM is now able to determine an absolute composition using neon synthetic isotope mixtures prepared with the gravimetric method from pure isotopes and to be assessed by NPL. Pure isotopes can also be iMERA Project of JRP - prepared by the Consortium having formally signed an agreement in 2007 - was not accepted for funding, all participants agreed to sustain these costs on their own resources.
In 2008, in addition to the reported expenses under Phase I, the activities continued in the frame of the signed iMERA JRP Agreement, and beyond until 2010: INRIM and VSL made new thermal measurements on samples containing natural neon of different sources, respectively five (three from NMIJ, NPL and PTB) and two (from INRIM); IRMM made new isotopic composition assays on natural neon and on pure isotopes, measurements that already extended to 2009. More thermal measurements are planned in 2009 by INRIM, INTiBS, NMIJ, LNE-INM/CNAM and NRC, also, additionally, on pure 22Ne and 20Ne sealed in new cells at INRIM, the only new determinations of Ttp after more than 35 years. IRMM is planning in 2009-2010 the calibration of their spectrometer with synthetic mixtures.
Activities under iii) - A CCT document on the 2007 knowledge situation was prepared for the 2008 meeting. Apart new publications, a final document is foreseen for the next CCT meeting in May 2010.