A High-Precision Tagged Neutron n-p Scattering Measurement at 14.9 MeV

The n-p scattering angular distribution was measured with 14.9 MeV incident neutrons produced at the neutron facility of Ohio University. The traditional time-of-flight technique with neutron-gamma discrimination was applied for the measurement of the number and energy of scattered neutrons. The scattering angle varied from 20 to 65 deg (laboratory system) in 5 deg incremental steps corresponding to an ejectile energy range from 13.16 to 2.66 MeV. The efficiency of the neutron detectors was measured in the energy range 2 to 9 MeV relative to the ²⁵²Cf standard and was calculated using Monte Carlo methods in the 2 to 14 MeV energy range. Two methods of analysis were applied for experimental and simulated data: a traditional approach with a fixed threshold ~0.1MeVee and a dynamic threshold approach. The efficiencies determined by both methods are in excellent agreement for simulated and experimental results within the energy interval 2 to 9 MeV. The experimental (<9 MeV) and calculated efficiencies (>9 MeV) were applied for evaluation of the n-p scattering experimental result. The corrections for neutron attenuation in the “scatter-detector” were calculated with analytical formulas and by the Monte Carlo method. Additional minor corrections for edge effect, C(n,n’)3α background and dead time were also included. The present data agree with recent evaluations for the n-p angular distribution within about 1.6%. The current state-of-the-art of experimental uncertainties that can be realized for a neutron counting experiment were reached in this investigation. An additional correlation analysis allows us to conclude that the standard deviation connected with existing correlations may be the main component of the total uncertainty.