A mobile detector for measurements of the atmospheric muon flux in underground sites

TL;DR

This paper presents a mobile detector system designed to measure underground muon fluxes, enabling estimation of site depths in water equivalent meters, with applications demonstrated in Romanian salt mines and surface locations.

Contribution

A novel mobile detector setup was developed and used to measure muon fluxes at various underground and surface sites, providing data for depth estimation and validation against simulations.

Findings

Muon flux measurements at different depths in Romanian salt mines.

Validation of measurements with Monte-Carlo simulations.

Demonstration of detector stability across locations.

Abstract

Muons comprise an important contribution of the natural radiation dose in air (approx. 30 nSv/h of a total dose rate of 65-130 nSv/h), as well as in underground sites even when the flux and relative contribution are significantly reduced. The flux of the muons observed in underground can be used as an estimator for the depth in mwe (meter water equivalent) of the underground site. The water equivalent depth is an important information to devise physics experiments feasible for a specific site. A mobile detector for performing measurements of the muon's flux was developed in IFIN-HH, Bucharest. Consisting of 2 scintillator plates (approx. 0.9 m2) which measure in coincidence, the detector is installed on a van which facilitates measurements at different locations at surface or underground. The detector was used to determine muon fluxes at different sites in Romania. In particular, data were taken and the values of meter water equivalents were assessed for several locations from the salt mine from Slanic Prahova, Romania. The measurements have been performed in 2 different galleries of the Slanic mine at different depths. In order to test the stability of the method, also measure- ments of the muon flux at surface at different elevations were performed. The results were compared with predictions of Monte-Carlo simulations using the CORSIKA and MUSIC codes.