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Date: | Mon, 25 Oct 1999 08:58:15 +0200 |
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I have freshly subscribed this list having heard of it from a
colleague of NIST (Wes Tew) in US.
I am not a geochemist, but instead a metrologist working in low
temperature thermometry at IMGC, the equivalent in Italy of NIST.
In thermometry, the International Temperature Scale of 1990 (ITS-90)
is using the triple point of hydrogen as a definition fixed point. We
are able to reproduce the temperature of this state for any
high-purity (typ 6N) sample to better than 0.1 mK. At this level, the
D content in "hydrogen" is critical: a change from the VSMOW value to
zero would change the triple-point temperature by about 1 mK.
Until a few weeks ago no one of us, thermometrists, was aware of the
fact the the actual content of D in H is not necessarily the VSMOW
and can be so variable. Everybody was assuming the VSMOW as fixed and
in the ITS-90 we did not put any specific warning and any
specification about that, meaning that we assumed "natural" abundance
for "hydrogen" as an isotopic mixture.
By chance, talking recently with a gas supplier, I went aware of the
fact that D content can be very different in commercial hydrogen of
different sources and batches. I was also informed by Wes of the
existance of this discussion list and I took a look of your archives
on the web.
As thermometrists we are EXTREMELY interested in interacting with all
people, like you, that have experience and data on this subject
matter: I am talking of gaseous hydrogen with a purity from 5N to 7N
that can be obtained from commercial supplier around the world, that
you probably use as reference material in your studies.
We will need to update the definition of the ITS-90 about this point
as soon as possible (we have a formal meeting in April 2000) to avoid
a very large increase of the uncertainty in this part of the ITS-90
and, consequently, we will need to perform new measurements on
different H-D mixtures at least in the range of the values that can
be found in commercial gases. Not all the gas manufacturers are
measuring the D content, and even less of them routinely. Not many of
them can provide acertificate of analysis specific of the lecture
bottle, especially for the isotopic composition.
I will be grateful to everybody of you that could supply me
information about the actual state-of-the-art.
Sincerely
Franco Pavese
--ATTENTION: please do not use anymore the addresses:
[log in to unmask],
[log in to unmask]
nor the phones:
+39 11 3977 341 nor FAX +39 11 3977 347
------------------------------------------------------------------------
Dr. Franco Pavese
CNR - Istituto di Metrologia "G.Colonnetti"
strada delle Cacce 73
10139 Torino, Italy
tel. ATTENTION +39 011 3977 341
FAX ATTENTION +39 011 3977 347
e-mail: [log in to unmask]
e-mail home: [log in to unmask]
cellular-phone: 0348 8130101
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