  The Thermo Scientific P385 Neutron Generator is a compact neutron source,
producing 14 MeV neutrons through the deuterium-tritium (DT) fusion reaction.
For practical use, it is important to measure and preferably understand the
dependence of the neutron production rate on the accelerator current and
voltage. In this study, we evaluated neutron production with a neutron
spectrometer (BTI N-Probe), a He-3 detector surrounded by HDPE shells (Nested
Neutron Spectrometer, NNS), and two ZnS fast neutron scintillators (EJ-410) for
both P385 A3082 and A3083 sealed tubes. We also predicted the neutron yield
using the TRIM code, which calculates the trajectory and the energy loss of
deuterons and tritons within the target. Experimental and theoretical results
showed a linear dependence on beam current and a $\sim$3.5 power law dependence
on the operating voltage. A series of NNS measurements, neutron spectrum from
N-Probe and MCNP calculation showed that the A3083 and A3082 tubes provide a
maximum neutron yield of $\sim 8.2 \times 10^8$ n/s and $\sim 4.5 \times 10^8$
n/s, respectively. We showed that tritium decay was not a significant
contributor to this difference.
