Proton recoil spectroscopy 400 meters from a fission neutron source

Neutron kerma and spectrum measurements have been made at the US Army Pulse Radiation Facility (APRF) to 400m in an air-over-ground geometry from a fission neutron source and have been compared to Monte Carlo transport calculations. The neutron spectra measurements were made using a rotating neutron spectrometer. This spectrometer consists of four spherical proton-recoil detectors mounted on a common rotating base. Detector radius, gas composition, and pressure have been varied to allow sensitivity over a neutron range of 50 keV to 4.5 MeV. Neutron kerma was determined by using the Kerr soft-tissue kerma factors. Measured neutron kerma agreed with the calculated neutron kerma to within 5%. Comparisons with other neutron spectrometers such as NE213 and Bonner Spheres are presented and agreement between the different spectrometers is better than 20%