Measurements of fast neutrons above ground and in 47 m depth with a He proportional counter

Neutrons contribute to the background of low radioactivity measurements, especially with detectors in large lead shields above ground, and to a lower extent in underground laboratories of medium depth. We measured the natural neutron flux in the energy region of fission by commercial He filled proportional counters at different places above ground and in an underground laboratory, which is covered by 47 m of rock, and demonstrated the drastic reduction of the neutron flux in the underground and the influence of the materials of the environment.