A logic flaw pointed out during a lab visit on a previous post of mine on the topic of what diffractometer would be the best to get: What will you be using this/these diffractometers for? Wouldn't this dictate then what XRD "geometries" would be optimal? e.g., Bragg-Brentano, Stoe capillary system with PSD, INEL PSD, etc? ------------------------- If money is no object - something to consider. Gordon Cressey and Paul Schofield at the Natural History Museum put a Bede Microsource X-ray system on their PSD (an on loan system) and had an amazing increasing in brightness of 1400 times over a sealed tube system (50 micron pin-hole of the focussed 0.3mm spot). The increase in diffracted intensity was 30 times with a 0.3mm spot from the microsource compared with a 5mmx0.3mm line from a sealed tube. Water is necessary on the microsource but it is only a trickle compared to other sealed tube or rotating anode systems. Gordon submitted an applications note (number 8) which does not seem to be on the Bede site but could be asked for. http://www.bede.co.uk I don't hold shares in the company but am presently analysing data collected on the sealed tube (2min) vs microsource (2min) INEL PSD data and the microsource is much nicer due to better counting stats. Considering inserting a Microsource over a sealed tube or rotating anode could be worth invenstigating depending on the application. Microsources are almost portable (~30 kG and size of two coke cans for the source) Lachlan. Forwarded message: > From [EMAIL PROTECTED] Thu Jul 6 23:16:33 2000 > Date: Thu, 06 Jul 2000 17:03:49 -0700 > To: [EMAIL PROTECTED] > From: [EMAIL PROTECTED] (Joe Reibenspies) > Subject: mirror vs. Ge monochromator. > X-Loop: [EMAIL PROTECTED] > > > 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] > ------------------------------------------------------------ > -- Lachlan M. D. Cranswick Collaborative Computational Project No 14 (CCP14) for Single Crystal and Powder Diffraction Daresbury Laboratory, Warrington, WA4 4AD U.K Tel: +44-1925-603703 Fax: +44-1925-603124 E-mail: [EMAIL PROTECTED] Ext: 3703 Room C14 http://www.ccp14.ac.uk
