Dear isogeochem people

Does anyone, preferably in the UK or Europe, have a spare magnet from a VG
602 hyudrogen mass spec.  If so, please would it be possible to borrow it
to make comparisons between the corrected data from a SIRA series 2 and
what we believe to be true values from the old VG 602 mass spec.

We have been investigating the reasons why we do not get the true value for
the delta 2H difference between SMOW and SLAP when measured on the SIRA
series 2 mass spec.  We have found out that the branched flight tube
restricts the mass 2 beam so that it is not fully measured.  Using the
stretch scaling factor brings GISP back to an acceptable value but I am not
yet convinced that it is absolutely correct.  Luckily we have an old SIRA
12 with a siamese H/D tube on it but no magnet, unfortunately.

If anyone has an old 602 which they have kept for parts or a magnet from
one it would be very helpful if we could borrow it to make comparisons on
the same gases in the same lab on the two machines.  The data we produced
many years ago on a 602 when we published the zinc method gave -426.7 per
mil, uncorrected by any stretch factor.  Now we can get values as high as
-350 per mil !!!

With reference to a previous discussion, I think that getting the answer
right is more important than referring to it relative to SMOW or V-SMOW.

Has anyone else made a comparison of SIRA series 2 or SIRA 10 and real data
and has anyone else also been getting very heavy uncorrected delta D values
from a SIRA?

(Editorial note especially for Jim O'Neil and Zach Sharp: please note that
contrary to my normal speaking manner, I have used delta D and not del D).

Max Coleman


_______________________________________________________________________
Max Coleman, Professor of Sedimentology
Postgraduate Research Institute for Sedimentology
The University of Reading
PO Box 227, Whiteknights
Reading RG6 6AB, UK

Phone    +44 1734 316627
Fax      +44 1734 310279
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