Neutron Scattering LengthsA very good resource to generate this data is Neutron Scattering Lengths on the Web
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Neutron Scattering Lengths vs. LambdaVia the Rietveld Users Mailing List at http://www.unige.ch/crystal/stxnews/riet/welcome.htm
Date: Tue, 23 Jan 2001 11:26:53 -0800 From: Holger Kohlmann [kohlmann@physics.unige.ch] X-Accept-Language: en To: Rietveld_l@ill.fr Subject: Re: neutron scattering lengths vs. lambda > Does anyone has a reference concerning the dependence of several neutron > scattering length (b) as a function of wavelength. I know that, like for > x-ray, some resonnance can appear. > A colleague of mine is experiencing some problems in fitting an holmium > compound at lambda=2.4266 angstrom and thinks this could related to a > different b at this wavelength than the one tabulated in [Sears, Neutron > News, 3(3) 1992 26] and fullprof (8.01fm). Moreover Lazy Pulverix seems to > use b=8.50fm. The neutron scattering length does not vary with the wavelength for thermal neutron except for nuclides which contain significant resonance effects. Most of them are lanthanides and for those data can be found in J. E. Lynn, P. A. Seeger, Resonance Effects in Neutron Scattering Lengths of Rare-Earth Nuclides, Atomic Data and Nuclear Data Tables 1990, 44, 191-207. Holmium, however, is not listed with these nuclides, i. e. apparently it does not show resonance effects up to 0.5 eV (>0.4A), and the variation of the scattering length with the wavelength should be neglegible for thermal neutrons. The problem with the your friend's fit must be something else. By the way, the latest version of GSAS can handle now those nuclides where resonance effects occur, e. g. 113-Cd, 149-Sm, 151-Eu, etc, and computes the scattering lengths correctly. A paper where this has been used for a neutron diffraction study of europium deuterides will soon be published in Journal of Alloys and Compounds. - Holger Kohlmann ___________________ Dr. Holger Kohlmann High Pressure Science and Engineering Center Department of Physics University of Nevada, Las Vegas 4505 South Maryland Parkway Las Vegas, Nevada 89154-4002 USA |