The High Efficiency Neutron Spectrometry Array (HENSA) is a detection system based on the Bonner Spheres principle [THO02]. In order to be sensitive at different energy ranges, HENSA is composed by ten independent long 3He-filled proportional counters embedded in High Density PolyEthylene (HDPE) moderators with different sizes. The neutron flux spectrum is unfolded from the experimental counting rates by means of appropriate reconstruction algorithms. Key to the reliability of the reconstruction process is the use of a priori information. This is typically achieved by means of Monte Carlo calculations or from previous measurements.
Early versions of HENSA have already been used for the characterization of the neutron background at the Canfranc Underground Laboratory (LSC), before the start of the scientific experiments [JOR13], and in the shallow underground facility Felsenkeller in Dresden [GRI20]. Currently, a long term characterization of the neutron flux is being carried out the LSC: in hall A from October 2019 [ORR21] and in hall B since March 2021 [MON21]. Measurements in hall B are foreseen during 2022 and 2023.
The HENSA/ANAIS collaboration aims for the precise determination of the neutron flux at hall B of the Canfranc Underground Laboratory, that could affect ANAIS-112, an experiment looking for the dark matter annual modulation using NaI scintillators [AMA21]. In this work we present and discuss the current status of the measurements in hall B of the LSC. In addition, FLUKA Monte Carlo calculations of the neutron flux spectrum at the LSC will be reported.
This work has been supported by the Spanish Ministerio de Economía y Competitividad under grants FPA2017-83946-C2-1 & C2-2 , PID2019-104714GB-C21 & C22, PID2019-104374GB-I00 and RTI2018-098868-B-I00. We also acknowledge the Generalitat Valenciana Grant No. PROMETEO/2019/007.
[AMA21] J. Amaré et al., Physical Review D 103, (2021) 102005.
[GRI20] M. Grieger et al., Physical Review D 101 (2020) 123027.
[JOR13] D. Jordán et al., Astroparticle Physics 42 (2013) 1.
[MON22] N. Mont-Geli et al., Journal of Physics: Conference Series 2156 (2022) 012169.
[ORR22] S. E. A. Orrigo et al., Journal of Physics: Conference Series 2156 (2022) 012223.
[THO02] D.J. Thomas and A.V. Alevra, Nuclear Instruments and Methods A 476 (2002) 12–20.