An Absolute Measurement of of Cf²⁵²

An absolute determination of the average number of neutrons, , emitted in the spontaneous fission of Cf²⁵² has been made by counting the fission neutrons in a large liquid scintillator. The detection efficiency of this counter was measured as a function of neutron energy. Well-collimated neutrons were scattered into the scintillator by an anthracene crystal, which detected the corresponding recoil protons. Pulse-shape discrimination was employed to eliminate γ-ray background. The average number of prompt neutrons emitted per Cf²⁵² fission was found to be 3.799 ± 0.034.