Measurements and Calculations of the Electron Recoil Spectra from Gamma Rays Emitted by Nitrogen for a 14-MeV Neutron Source

The electron recoil spectra from gamma rays produced by the interaction of 14-MeV neutrons with 0.5, 1.0, 3.0, and 7.0 mean-free-paths (mfps) of nitrogen have been measured with NE-213 scintillators positioned at 26, 30, and 120 deg at distances ranging between 7 and 10 m. Thin wall spherical Dewars filled with liquid nitrogen, with radii dimensions equivalent to the above number of mfp, were bombarded with a centered nominal 14-MeV neutron source. Calculations of the gamma and recoil electron spectra have been carried out with the ENDF/B-IV and ENDL neutron-gamma libraries. Comparison between the measured and calculated electron recoil spectra shows that the discrepancies are not larger than 10%. This agreement implies that the calculated gamma-ray spectra are expected to give a good description of the gamma transport in nitrogen from a 14-MeV neutron source.