Natale (and others!)
We have a very new D8 equipped with dual Goebel mirrors (40mm primary and
secondary), but have no experience with the Vario monochromator (very fiddly
to keep well aligned so I'm told). We've just used the reflection geometry
so far, as we haven't even got around to mounting the capilliary holder yet.
Therefore these are observations from a short period of use.
With regard to structure determination and use of the Goebel mirrors there
are some things to be noted. The Bruker field personnel have very little
experience with installing and aligning the diffracted beam mirror (i.e. I
did it myself - not too difficult though once you've worked it out, but much
patience required). I understand that the situation in Europe isn't much
better. However with a mirror system it is desirable to have the second
mirror to regain some of the resolution lost with just the primary one, as
well as increased intensities over the alternative flat LiF or graphite
monchromators, whilst also removing fluoresence. Despite the increased
resolution it is still not as good as the D8 Bragg-Brentano setup, but
better than the old Scintag we had. Now it is set up I am extremely
satisfied with it - user errors in sample preparation with regard to
displacement are not an issue, making it a potentially very good general
user instrument as well as with high temperature furnaces. The mirrors do
not remove Ka2, so if this is a requirement they are not suitable.
One thing which is very apparent with the 660 LaB6 standard, but not so much
with actual samples, is significant axial divergence (even with the supplied
Soller slits), which means care needs to be taken with regard to peak
profiles. I have successfully refined some simple structures using GSAS and
Topas so it's not a major problem.
I would imagine that most of my observations will hold true for mirror
systems from other manufacturers as the geometry is basically the same.
Best regards
Pam Whitfield
Dr Pamela Whitfield CChem MRSC
Energy Materials Group
ICPET
Building M12
National Research Council
Montreal Road
Ottawa ON
K1A 0R6
Canada
Tel: (613) 991-2435 / (613) 998-8462
Fax: (613) 991-2384
Email: [EMAIL PROTECTED]
-----Original Message-----
From: Natale Perchiazzi [mailto:[EMAIL PROTECTED]]
Sent: July 5, 2001 6:19 AM
To: [EMAIL PROTECTED]
Subject: what diffractometer
Dear All,
we are planning to purchase a new diffractometer, which will be mostly
devoted (but not exclusively) to structure determination. We will mainly
study organometallic compounds and silicate minerals, working both in
transmission and reflection geometry.
Two possible choices for Siemens D8 equipment maybe VARIO (focusing primary
monochromator) and Gobel mirror systems, both of which seem rather
promising.
What is your experience on these systems? Did you experience other
diffractometers with similar capabilities from other companies?
Replies will be warmly welcome.
Thanks for your attention Natale Perchiazzi
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dr Natale Perchiazzi
Dipartimento di Scienze della Terra
Universitą degli Studi di Pisa
Via S.Maria 53, I-56126 Pisa
tel +39 050 847269
fax +39 050 500932
e-mail [EMAIL PROTECTED]
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