Barometric pumping effect for radon-due neutron flux in underground laboratories

TL;DR

This study investigates how barometric pressure variations influence neutron flux in underground labs, revealing a radon-related pumping effect that causes significant neutron flux fluctuations over time.

Contribution

It demonstrates a correlation between barometric pressure and neutron flux, attributing the effect to radon barometric pumping in underground environments.

Findings

Neutron flux increases up to 3 times during certain pressure conditions

The effect is linked to radon-induced (alpha,n) reactions in surrounding rock

The phenomenon is observed over a 3-year period in an underground laboratory

Abstract

It is known that neutron background is a big problem for low-background experiments in underground Laboratories. Our global net of en-detectors sensitive to thermal neutrons includes the detectors running both on the surface and at different depths underground. We present here results obtained with the en-detector of 0.75 m^2 which is running more than 3 years in underground room at a depth of 25 m of water equivalent in Skobeltsyn Institute of Nuclear Physics, Moscow. Spontaneous increases in thermal neutron flux up to a factor of 3 were observed in delayed anti-correlation with barometric pressure. The phenomenon can be explained by a radon barometric pumping effect resulting in similar effect in neutron flux produced in (alpha,n)-reactions by alpha-decays of radon and its daughters in surrounding rock