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 197 Au(n, (cid:1) ) 198 Au interaction. The measurements made for 0-100 cm in fresh water and 20-400 cm in sea water showed that the thermal neutron flux showed peak at around 10 cm depth and then gradually decreased with depth in water. The depth profiles in seawater were almost the same profile as freshwater. In the case of soil made for 0-60 cm, thermal neutron flux showed a peak at 5 cm then through a shoulder-like decrease during 10~30 cm range and decreased with depth gradually rapidly to 60 cm.