Experimental Determination of Fraction of NeutronsBelow 1.5 MeV for Am-Be Neutron Source

A practical method for experimentally determining the fraction of neutrons below 1.5 MeV for the Am-Be neutron source is described. The partial neutron spectrum (the n₁ group) was measured by time of flight accompanied with the 4.438 MeV γ-ray. The fraction of neutrons below 1.5 MeV was derived from the 4.438 MeV γ-ray to total neutron ratio and the ratio of the area of the n₁ group spectrum to the measured total spectrum above 1.5 MeV normalized at the peak near 3.2 MeV. The fraction of neutrons with energies below 1.5 MeV amounts to (19.1±1.9)% for the Chinese-made Am-Be neutron source.