Eur. Phys. J. Plus (2022) 137: 210
https://doi.org/10.1140/epjp/s13360-022-02407-1

Regular Article

Gamma-ray flux measurement and geotechnical studies at the selected site for the LABChico underground laboratory

¹ Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Ciudad de México, México
² Centro Atómico Bariloche, CNEA/CONICET/IB, Bariloche, Argentina
³ Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, 04510, Ciudad de México, México
⁴ Royal Holloway, University of London, Egham Hill, United Kingdom
⁵ Instituto de Física, Universidad Nacional Autónoma de México, 01000, Ciudad de México, México
⁶ Facultad de Ingeniería, Universidad Nacional Autónoma de México, Ciudad de México, México
⁷ Boulby Underground Laboratory, Boulby Mine, Saltburn-by-the-Sea, United Kingdom
⁸ Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom
⁹ Departamento de Física, FES-Cuautitlán, Universidad Nacional Autónoma de México, C.P. 54770, Estado de México, México

Received: 26 May 2021
Accepted: 10 January 2022
Published online: 8 February 2022

Abstract

The $\gamma$-ray flux inside La Guadalupe mine, the selected site for the construction of the underground laboratory LABChico in Mexico, is reported for energies below 3 MeV. Data were recorded with a 0.669 kg thallium-activated sodium iodide (NaI) crystal detector deployed for 3.6 hr. The detector response was calculated via Monte Carlo simulations with GEANT4 and validated against point-like calibration sources, and the $\gamma$-ray spectrum was extracted using an unfolding technique. The $\gamma$-ray flux above 250 keV and below 3 MeV is 0.1768 $\gamma$/cm${}^2$/s. The two most intense $\gamma$-rays in the natural radioactive background, ${}^{40}$K and ${}^{208}$Tl, were identified. The flux measured for these isotopes is 0.0363 ± 0.0020 $\gamma$/cm${}^2$/s and 0.0016 ± 0.0005 $\gamma$/cm${}^2$/s, respectively. A $\gamma$-ray spectrometry analysis of rock samples showed 674.0 ± 2.0 Bq/kg, 24.0 ± 0.1 Bq/kg, and 17.7 ± 0.2 Bq/kg, of ${}^{40}$K, ${}^{232}$Th, and ${}^{238}$U, respectively. These results are compared with deep underground facilities such as SURF, SNOLAB, Boulby, Modane, and Gran Sasso, with differences observed mainly due to the rock composition. Geotechnical studies of the mine and its rock composition are also reported.