Asymptotic behavior of neutron small-angle multiple scattering spectra

The asymptotic behavior of the spectra for large values of the scattering v ector for the case of elastic multiple small-angle neutron scattering (SANS ) is investigated theoretically and experimentally. An expansion of the spe ctrum in terms of the reciprocal of the magnitude of the momentum transfer is obtained taking account of the influence of the instrumental line. It is shown that, to within some factor, the leading term of the expansion is id entical to the differential single-scattering cross section averaged over a statistical ensemble of particles; several subsequent terms in the expansi on are calculated and the range of applicability of the resulting expressio ns is determined. The asymptotic behavior of the multiple SANS spectrum is measured, using a two-crystal neutron spectrometer, for samples of an HTSC ceramic, the alloy Fe-Ni, and Al powder. The agreement between the experime ntal results and the theoretical predictions is analyzed. (C) 1998 American Institute of Physics. [S1063-7761(98)02312-9].