College Park, Maryland      June 6 - 10 , 2004

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TP36: Some Effects of Multiple Scattering Encountered in SANS

J. G. Barker (NIST Center for Neutron Research)

General methodologies for calculating multiple scattering effects are presented. Several specific examples of multiple scattering corrections found in small angle neutron scattering (SANS) are presented. The cases presented here were chosen to provide particular insights into the more routine problems encountered in handling multiple scattering, but as yet have not been sufficiently espoused in the considerable literature on this subject. For scattering occurring at sufficiently small angles, the semi-analytical technique of Schelten & Schmatz [J. Appl. Cryst. (1980), 13, 385-390] was used. Monte Carlo simulations were also used, and were found to be a more robust method of calculating many problems. Power series corrective expressions have been determined for the forward cross-section I_m(0), and the radius of gyration R_g, used to characterize the central part of the scattering curve for five different scattering functions: Gaussian shaped scattering, the scattering from spheres, the DAB model, the Sabine function (p = 3/2) and Lorentzian scattering. Other cases presented are scattering from narrow Gaussian peaks, and corrections to power-law scattering at large q. Effect of multiple scattering upon the forward cross-section of isotropically scattering samples, such as from water and vanadium, are also presented.

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