Abstract
We describe a new concept for a neutron moderating assembly resulting
in the more efficient production of slow neutron beams. The
Convoluted Moderator, a heterogeneous stack of interleaved moderating
material and nearly transparent single-crystal spacers, is a
directionally-enhanced neutron beam source, improving beam
effectiveness over an angular range comparable to the range accepted
by neutron beam lines and guides. We have demonstrated gains of 50%
in slow neutron intensity for a given fast neutron production rate
while simultaneously reducing the wavelength-dependent emission time
dispersion by 25%, both coming from a geometric effect in which the
neutron beam lines view a large surface area of moderating material in
a relatively small volume. Additionally, we have confirmed a
Bragg-enhancement effect arising from coherent scattering within the
single-crystal spacers. We have not observed hypothesized refractive
effects leading to additional gains at long wavelength. In addition
to confirmation of the validity of the Convoluted Moderator concept,
our measurements provide a series of benchmark experiments suitable
for developing simulation and analysis techniques for practical
optimization and eventual implementation at slow neutron source
facilities.
