NEUTRON FOCUSING USING CAPILLARY OPTICS

Using the principle of multiple mirror reflection from smooth surfaces at small grazing angles, polycapillary fibers of narrow inner channel s (diameter of a few micrometers) have been used to transport and bend slow neutron beams. Neutrons in the cold and thermal range have been focused to a small spot to produce significant gains (approximately x 10) in intensity. We report studies of neutron transmission properties of individual capillaries, using cold and thermal neutrons at the CNR F (Cold Neutron Research Facility) of the NBSR (the 20 MW research rea ctor at the National Institute of Standards and Technology, USA). Seve ral aspects of these properties are investigated, namely, the transmis sion as a function of bending curvature, of length of the fibers, and of composition of fiber materials. From these studies we obtain inform ation on the critical angle of reflection, the reflectivity, and the r oughness of the inner surface. We also report the characterization of the first prototype neutron lens constructed at the Kurchatov Institut e in Moscow and show that a focal point of 1 mm has been achieved. Fin ally we discuss the design of a lens suitable for neutron absorption e xperiments at the end of a neutron guide.