Variation of environmental neutron flux with the depth of water and soil

As a part of interest in the study of the neutron flux in biological environments, variations of slow neutrons with depth of water and soil were measured through the radioactivity induced in gold by 197Au(n,γ)198Au reaction. The measurements made for 0-100 cm in fresh water and 20-400 cm in sea water showed that the thermal neutron flux had a peak at around 10 cm depth and then gradually decreased with depth in water. The depth profile in sea-water was almost the same as freshwater. In the case of soil made for 0-60 cm, thermal neutron flux showed a peak at 5 cm and decreased rapidly to 60 cm accompanying a shoulder-like shape during 10-30 cm range. (author)