Some focusing techniques and their application to low-angle neutron scattering.

Both imaging and simple converging collimator systems can provide a focused neutron beam. Each system has been tested and appears suitable for exploitation. Imaging systems employing bent multilayer monochromators can be made simply by elastically bending a flat multilayer. The periodic spacing of the multilayer can be made to match that of the sample. The converging Soller slit provides a purely geometric means of prouducing a focused beam. Wavelength spread and distribution across the beam can be controlled separately. Soller-slit technology is further advanced than that of multilayers. The experiments sketched above demonstrate that converging or focused neutron beams suitable for low-angle scattering work can be produced with existing technology. Focusing incurs little or no loss of intensity and does not seriously distort the resolution function of a low-angel instrument. It permits a small spectrometer to make use of both advanced detector technology and large samples and thus to approach the capability of a much larger machine.