Low energy neutron background in deep underground laboratories

TL;DR

This paper measures and compares the thermal neutron flux in several deep underground laboratories to inform shielding design and improve experimental sensitivity in rare event physics.

Contribution

It provides the first comprehensive set of absolute thermal neutron flux measurements across multiple major underground labs.

Findings

Neutron flux varies significantly between sites.

Data aids in optimizing shielding for underground experiments.

Establishes baseline neutron background levels for future research.

Abstract

The natural neutron background influences the maximum achievable sensitivity in most deep underground nuclear, astroparticle and double-beta decay physics experiments. Reliable neutron flux numbers are an important ingredient in the design of the shielding of new large-scale experiments as well as in the analysis of experimental data. Using a portable setup of He-3 counters we measured the thermal neutron flux at the Kimballton Underground Research Facility, the Soudan Underground Laboratory, on the 4100 ft and the 4850 ft levels of the Sanford Underground Research Facility, at the Waste Isolation Pilot Plant and at the Gran Sasso National Laboratory. Absolute neutron fluxes at these laboratories are presented.