Development of high efficiency neutron detectors and measurement of low-level environmental and cosmic-ray neutrons

The high-efficiency moderated-type neutron spectrometer and dose-equivalent counters were developed for the measurement of low-level environmental neutrons. By using these detectors, the neutron energy spectra and dose equivalent rates due to skyshine effect were measured in the environment surrounding the accelerator facilities and also the altitude variation of cosmic-ray neutrons in the aircraft on flying over Japan. The two types of high-efficiency dose-equivalent counters were realized by using 10 atm 3He counter having a diameter of 5.08 cm and 5 atm 3He counter having a diameter of 12.7 cm. These two counters have about 10 and 70 times higher sensitivities, respectively, than the commercially available dose-equivalent counters. These counters are now in practical use for routine monitoring in the environment around the accelerator facilities. (author)