  Thick target deuteron breakup is a variable-energy accelerator-based source
of high-energy neutrons, with applications in fundamental and applied nuclear
science and engineering. However, the breakup mechanism remains poorly
understood, and data on neutron yields from thick target breakup remains
relatively scarce. In this work, the double-differential neutron yields from
deuteron breakup have been measured on a thick beryllium target at
$\epsilon_d=33$ and 40 MeV, using both time-of-flight and activation
techniques. We have also introduced a simple hybrid model for the
double-differential deuteron breakup cross section, applicable in the
$\epsilon_d=10$--$100$ MeV energy range on light ($Z\leq 6$) targets. This
model features four empirical parameters that have been fit to reproduce
experimental breakup measurements on beryllium targets, using the method of
least-squares. It was shown that these parameters extrapolate well to higher
energies, and to other low-Z target materials. We also include optimization of
the parameters that modify the Kalbach systematics for compound and
pre-equilibrium reactions, in order to better reproduce the experimental data
for beryllium targets at large angles.
