  The design of a neutron source capable of producing 24 and 70 keV neutron
beams with narrow energy spread is presented. The source exploits
near-threshold kinematics of the $^{7}$Li(p,n)$^{7}$Be reaction while taking
advantage of the interference `notches' found in the scattering cross-sections
of iron. The design was implemented and characterized at the Center for
Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory.
Alternative filters such as vanadium and manganese are also explored and the
possibility of studying the response of different materials to low-energy
nuclear recoils using the resultant neutron beams is discussed.
