Speaker
Description
Underground laboratories are key facilities for the study of rare phenomena. The attenuation of cosmic rays and secondary by-products like gamma rays, electrons and muons by several orders of magnitude provide a low background environment that is suitable for experiments dealing with dark matter, neutrinoless double beta decay, measurement of cross sections of astrophysical reactions, etc. However, there is still a background composed of neutrons from spontaneous fission and $\alpha$-n reactions produced in the rocks surrounding the laboratories that needs to be characterized and even monitored.
In the last years, CLYC detectors are gaining interest due to their good discrimination properties between gamma rays an neutron particles, and could potentially be used in underground facilities. In this work, we have used two CLYC detectors to measure thermal neutron flux. CLYC detectors present an intrinsic alpha activity that overlaps with the region of interest for thermal neutrons. Thus, detectors had to be thoroughly characterized for their use in low background conditions, and a dedicated pulse shape analysis was developed to obtain the neutron flux.
The thermal neutron flux was also measured using He-3 detectors. In this case, the spectra also show contributions from other signals apart from neutrons: gamma rays, microdischarges and intrinsic alpha activity from the cathode. A pulse analysis was also developed to obtain a clean neutron spectrum and the thermal neutron flux.
The neutron flux was compared with the one obtained with the CLYC detectors, finding a good agreement between both measurements. The flux was also monitored for several months to observe the possible changes in the thermal neutron background, finding no remarkable changes within the statistical fluctuations.
