Neutron long wavelength cut-off filter

We report the first use of a long wavelength cut-off filter for a polarized cold neutron beam. If a supermirror polarizer is used, the degree of polarization of neutrons with relatively long wavelengths, say, longer than 1.3 nm, is poor and difficult to determine. The filter we used in this paper separates these undesired neutrons from the beam. The device is 8 mm long and consists of a stack of 118 Si wafers, whose surfaces are covered with m = 3 Ni/Ti supermirrors (see Fig. 1). The performance of this filter is described. (C) 2000 Elsevier Science B.V. All rights reserved.