Abstract
The cold polycrystalline beryllium reflector-filter concept has been
used to enhance the cold neutron emission of cryogenic hydrogen
moderators, while suppressing the intermediate wavelength and fast
neutron emission at the same time. While suppressing the fast neutron
emission is often desired, the suppression of intermediate wavelength
neutrons is often unwelcome. It has been hypothesized that replacing
the polycrystalline reflector-filter concept with a single-crystal
reflector-filter concept would overcome the suppression of
intermediate wavelength neutrons and thereby extend the usability of
the reflector-filter concept to shorter but still important
wavelengths. In this paper we present the first experimental data on a
single-crystal reflector-filter and compare experimental results with
hypothesized performance. We find that a single-crystal
reflector-filter retains the long-wavelength benefit of the
polycrystalline reflector-filter, without suffering the same loss of
important intermediate wavelength neutrons. This finding extends the
applicability of the reflector-filter concept to intermediate
wavelengths, and furthermore indicates that the reflector-filter
benefits arise from its interaction with fast (background) neutrons,
not with intermediate wavelength neutrons of potential interest in
many types of neutron scattering.
