Cosmic Ray Neutron Monitor for OGO-F

The objective of this experiment is to monitor the cosmic-ray neutron flux over a large region of space near the earth for an extended time with a simple neutron monitor. The basic detecting system to measure the integrated neutron flux from 10-8 to 15 MeV consists of a moderated He3 proportional counter surrounded by a charged-particle rejection system. A plastic scintillator viewed by a photomultiplier is operated in coincidence with the neutron counter to determine the energy spectrum and flux in the 1-10 MeV range. In order to minimize contributions from neutrons produced within the OGO spacecraft, the sensor is located about 4.5 meters out on the EP-5 boom. The experiment includes an in-flight calibrator to check pulse discriminator levels on neutron and charged-particle channels and a calibration-loop system to compensate for changes in the photo-multiplier gain. The mean neutron detection efficiency for the expected neutron energy spectrum over the energy range 10-8-15 MeV is 1.8 cm2. The weight of the neutron sensor is 2.58 kg, with a length of 0.314 meter and a diameter of 0.111 meters. The total power requirements are 4.5 watts.