Cosmic neutron intensity at sea level near the zero degree geomagnetic latitude

The cosmic neutron intensity at sea level was monitored in the South China Sea where the vertical cut-off of geomagnetic rigidity is highest. The lowest neutron intensity, measured near the geomagnetic latitude at zero degrees, is 1.13 ± 0.12 n Sv h−1. Land survey on the nearby coral reef yields a lower reading. Shipboard data in the open sea are also compared to those measured in harbors and further inland. The progressive decrease of cosmic neutron dose rates from ship to ground indicates that the air-sea-land interfaces play an essential role in attenuating the cosmic neutron intensity.