  An electron beam may be used to generate bremsstrahlung photons that go on to
create photoneutrons within metals. This serves as a low-energy neutron source
for irradiation experiments [1-3]. In this article, we present simulation
results for optimizing photoneutron yield for a 10-MeV electron beam on
tantalum foil and erbium deuteride (ErD$_3$). The thickness of the metal layers
was varied. A tantalum foil thickness of 1.5 mm resulted in the most photons
reaching the second metal layer. When a second metal layer of ErD$_3$ was
included, the photoneutron yield increased with the thickness of the secondary
layer. When the electron beam was directly incident upon a layer of ErD$_3$,
the photoneutron yield did not differ significantly from the yield when a layer
of tantalum was included. The directional photoneutron yield reached a maximum
level when the thickness of the ErD$_3$ layer was around 12 cm. About 1 neutron
was generated per $10^4$ source electrons. When using a 2-mA beam current, it
is possible to generate up to $10^{ 12}$ neutrons per second, making this
combination a relatively-inexpensive neutron generator.
