A new method of absolute neutron flux determination using an associated gamma-ray technique

Abstract

The 7Li(p,n 1γ) 7Be reaction is developed as a primary neutron standard for the determination of absolute neutron flux and neutron detector efficienty over a neutron energy range 0.350 ≤ E n≤2.8 MeV. A new associated γ-ray method is used, in conjunction with a neutron time-of-flight spectrometer, whose essential feature is that the associated γ-ray to neutron ratio is known. For the 7Li(p,n 1γ) 7Be reaction the ratio of the 431 keV γ-rays to n 1 neutrons is unity. It simplifies the method that the 431 keV γ-rays associated with the n 1 neutrons have an isotropic angular distribution. In this case, an accurate measurement of the 431 keV γ-rays emitted at any angle determines the total number of n 1 neutrons emitted independent of the 7Li(p,n 1) 7Be cross section, Li target thickness, and beam current. After the n 1 angular distributions are determined as a function of proton energy, the 7Li(p,n 1γ) 7Be reaction can be used to determine the absolute n 1 neutron flux at any angle by measuring the 431 keV γ-ray production, for this purpose, twelve n 1 neutron angular distributions have been measured between 3.1≲ E p≲4.9 MeV.