  We present the analysis and results of the first dataset collected with the
MARS neutron detector deployed at the Oak Ridge National Laboratory Spallation
Neutron Source (SNS) for the purpose of monitoring and characterizing the
beam-related neutron (BRN) background for the COHERENT collaboration. MARS was
positioned next to the COH-CsI coherent elastic neutrino-nucleus scattering
detector in the SNS basement corridor. This is the basement location of closest
proximity to the SNS target and thus, of highest neutrino flux, but it is also
well shielded from the BRN flux by infill concrete and gravel. These data show
the detector registered roughly one BRN per day. Using MARS' measured detection
efficiency, the incoming BRN flux is estimated to be
$1.20~\pm~0.56~\text{neutrons}/\text{m}^2/\text{MWh}$ for neutron energies
above $\sim3.5$ MeV and up to a few tens of MeV. We compare our results with
previous BRN measurements in the SNS basement corridor reported by other
neutron detectors.
