Monitoring of the thermal neutron flux in the LSM underground laboratory

S. Rozov , E. Armengaud (1) , C. Augier (2) , L. Bergé (3) , Alain Benoit (4) , O. Besida , J. Blümer , A. Broniatowski (5) , V. Brudanin , A. Chantelauze , M. Chapellier (5) , G. Chardin (5) , F. Charlieux (2) , S. Collin (5) , O. Crauste (5) , M. de Jesus (2) , X. Defay (6) , P. Di Stefano (2) , Y. Dolgorouki (5) , J. Domange (5) , L. Dumoulin (5) , K. Eitel , D. Filosofov , J. Gascon (2) , G. Gerbier (1) , M. Gros (1) , M. Hannawald (1) , A. Juillard (2) , H. Kluck , V. Kozlov , R. Lemrani (1) , A. Lubashevskiy , C. Marrache (5) , S. Marnieros (5) , X-F. Navick (1) , C. Nones (5) , E. Olivieri (3) , P. Pari (7) , B. Paul (1) , V. Sanglard (2) , S. Scorza (2) , S. Semikh , M-A. Verdier , L. Vagneron (2) , E. Yakushev

1 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
2 IPNL - Institut de Physique Nucléaire de Lyon
3 CSNSM INSTR
4 NEEL - HELFA - Hélium : du fondamental aux applications
5 CSNSM PS1
6 CSNSM - Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse
7 IRAMIS - Institut Rayonnement Matière de Saclay (DRF)

This paper describes precise measurements of the thermal neutron flux in the LSM underground laboratory in proximity of the EDELWEISS-II dark matter search experiment together with short measurements at various other locations. Monitoring of the flux of thermal neutrons is accomplished using a mobile detection system with low background proportional counter filled with $^3$He. On average 75 neutrons per day are detected with a background level below 1 count per day (cpd). This provides a unique possibility of a day by day study of variations of the neutron field in a deep underground site. The measured average 4$\pi$ neutron flux per cm$^{2}$ in the proximity of EDELWEISS-II is $\Phi_{MB}=3.57\pm0.05^{stat}\pm0.27^{syst}\times 10^{-6}$ neutrons/sec. We report the first experimental observation that the point-to-point thermal neutron flux at LSM varies by more than a factor two.

Domaines: Instrumentation et méthodes pour l'astrophysique [astro-ph.IM]; Instrumentation et méthodes pour l'astrophysique [astro-ph.IM]

S. Rozov, E. Armengaud, C. Augier, L. Bergé, Alain Benoit, et al.. Monitoring of the thermal neutron flux in the LSM underground laboratory. 2012. ⟨in2p3-00696140⟩