Monitoring the SNS basement neutron background with the MARS detector

TL;DR

This paper reports on the deployment of the MARS neutron detector at the SNS to monitor and characterize beam-related neutron background, providing flux estimates and comparison with previous measurements.

Contribution

First dataset collected with MARS at SNS for BRN background monitoring, offering new flux measurements and comparison with prior data.

Findings

Detected approximately one BRN per day.

Estimated neutron flux of 1.20 ± 0.56 neutrons/m²/MWh for energies above 3.5 MeV.

Compared results with previous neutron background measurements.

Abstract

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.