The characterization of a polycapillary neutron lens

Materials-analysis measurements that employ neutron-absorption techniques may benefit from cold neutrons that may be focused using a lens consisting of polycapillary fibers. An expression is derived for the intensity gain and the size of the beam along the beam path, including that at the focus, and a criterion is developed for the depth of focus. The gain in intensity at the focus depends not only on the design parameters of the lens but also on the divergence and wavelength of the incident beam. This analysis is applied to the two neutron lenses that have previously been tested.