Cosmic-Ray Neutrons in Water at an Altitude of 10 600 Feet

The neutron component of the cosmic radiation in the first 50-cm layer of water adjacent to the surface of a mountain lake, located at an altitude of 10 600 feet, was studied with the aid of a tray of ten enriched boron trifluoride filled counters connected in parallel. A measure of the thermal neutron intensity was obtained by alternately shielding the tray of counters with tin and cadmium of equal g ${\mathrm{cm}}^{-2\mathrm{}}$. A transition region was found to exist between the surface and the 30-cm level wherein the thermal neutron intensity decreased rapidly with depth. Below the 30-cm level, the thermal neutron intensity was found to be almost constant over an interval of 20 cm. The neutron production rate and thermal neutron flux, just below the transition region, were found to be 4.6×${10}^{-5\mathrm{}}$ neutrons ${\mathrm{g}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ and about 4.3×${10}^{-4\mathrm{}}$ thermal neutrons ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$, respectively.