When we faced the same decision (well, only one machine, UK oil money does
not filter back into Universities!), we opted to purchase a Bruker D5005
with a mirror. Our main reason was that the machine is primarily used for
non-ambient temperature work and some for thin films. The mirror does seem
to provide increased intensity on the sample (I'd guess a factor of 5 to 10
over a monochromator) and a parallel beam of X-rays, both of which are very
useful if your sample is sitting in a chamber that attenuates the beam and
may be moving up or down a bit as the temperature changes. The down sides
are that you still have the alpha 1/alpha 2 doublet, the peaks are
definitely broader, and there is some asymmetry to deal with. For example,
our D5000 (Ge mono-PSD) will produce peaks with a fwhm ca. 0.07 degrees,
when the same peak using the D5005 (Goebel mirror-PSD) will be ca. 0.15
degrees wide after alpha-2 stripping. However, we can perform good
Rietveld refinements with the data.
My suggestion would be that if you want the best resolution with short
counting times, and you are going to operate at room temperature, go with a
monochromator and PSD.
With regards alignment, our experience is that both types of optics are
sensitive! I think the design of the mount is critical, I suggest you
actually get a demo of an alignment procedure prior to purchase.
Joe Hriljac
>I wish to thank every one for their suggestions of instruments
>and software. As many of you know we (texas A & M) are about to
>purchase several x-ray powder diffractometers. Since money is
>not a concern (texas oil, thank-you mr. opec) we are concentrating
>on the optics and detectors. Our fist choice, in the optics, will be
>between choosing the (G) mirror or the Ge monochromator (or both?).
>Some time ago (1996 and 1998) this group touched on the subject.
>
>My question is this. The community has had some time to exam both
>the mirrors and the Ge monochromator for structural work. Which
>one appears to be the best choice? The Ge monochromator is robust
>but will also attenuate the xray flux (much more than the mirrors).
>The mirrors on the other hand are sensitive to alignment but have
>a higher throughput of the xray flux.
>
>Will the mirror (plus slits) produce a parallel beam that is
>free of alpha-2, good enough for fine structural work?
>
>I need an expert's opinion on this. Any comments?
>
>Thanks in advance
>
>J.Reibenspies
>
>------------------------------------------------------------
>Joseph H. Reibenspies Ph.D. Associate Research Professor
>Department of Chemistry Texas A & M University
>College Station, Texas 77842 (979)845-9125
>fx (979)845-8184 [EMAIL PROTECTED]
>------------------------------------------------------------
Joseph A. Hriljac tel: +44 (0)121 414 4458
Senior Lecturer fax: +44 (0)121 414 4403 or 4442
School of Chemistry email: [EMAIL PROTECTED]
University of Birmingham
Edgbaston
Birmingham B15 2TT
UK
