Design of the Small Angle Neutron Scattering instrument at the Indiana University Low Energy Neutron Source: Applications to the study of nanostructured materials

Abstract

The Low Energy Neutron Source (LENS) located at the Indiana University Cyclotron Facility (IUCF) is a prototypical long-pulse accelerator-based neutron source. The Small Angle Neutron Scattering (SANS) instrument is one of several planned instruments at the LENS facility. The SANS instrument is a time-of-flight instrument which utilizes a pinhole collimation system and neutron wavelengths up to 20A giving it a q range from about 0.006Å^-1 to 0.5Å^-1 with a maximum divergence at the sample of about ±8mrad. The neutron flux on the sample at the anticipated 8kW mode of operation is anticipated to be greater than 2 × 10⁴n/s.cm ². The design, calibration, and testing of the LENS SANS instrument is discussed, including Monte-Carlo simulations and analytical calculations used to optimize the collimation design, the placement and design of the pulse-overlap chopper system, and other aspects of the instrument's geometry. The expected resolution, count rates, and other general performance parameters of the instrument are presented and, where possible, compared with experimental results.

SANS measurements of a family of tripodal organo-silicon dendrimer molecules using the IPNS SAND and the NCNR NG3 SANS instruments are presented. Variations in the scattering curves are compared for solutions of the dendrimers at multiple concentrations in d-heptane, d-DCM, and d-toluene. Models of both the particle form factor and the structure factor are presented. The measurements suggest a distinct difference between the size and behavior of the highest generation dendrimer in two of the solvents (d-DCM and d-toluene) as compared to a third (d-heptane). Additionally, the dendrimer molecules appear to be forming short chains in solution.

A brief study of iron oxide magnetic nanoparticles is also presented. This study includes a presentation of the magnetic measurements of the nanoparticles using a SQUID magnetometer. The measurements indicate contributions by a larger dispersion of magnetic moments than is explained by the size dispersion of the particles. SAXS measurements help to confirm that this apparent dispersion in the magnetic moments is likely the result of aggregation and associated magnetic coupling between particles as well as the formation of distinct spinel and wustite phases in the particles. SANS measurements of the particles using the NCNR NG3 SANS instrument are also presented.