LOW-RESOLUTION SMALL-ANGLE SCATTERING USING NEUTRON FOCUSING OPTICS

Experiments at low values of scattering vector require tight collimati on in the primary beam, as well as the ability to make measurements wi th good spatial resolution on the detector. Because neutron sources ar e not as intense as X-ray sources, large source and sample areas are u sed, and long instruments are necessary for adequate resolution. Incre ased count rates may be obtained using collimated beams which converge to a point on the detector. Further increases may be obtained with co nverging guides in the form of a focusing lens to increase the effecti ve flux. Narrow guides enable the spectrometer dimensions to collapse for the same resolution. The critical angle of the fibers forming the focusing lens dominates the resolution, and such an instrument is usef ul only for low resolution measurements. However the greatly reduced l ength is only valuable if there is a high resolution detector to match the dimensions of the guide.