Average Number of Prompt Neutrons Emitted in the Spontaneous Fission of U238and Pu240

Abstract
The average number, ῡ, of prompt neutrons emitted in the spontaneous fission of U238 and Pu240 has been measured relative to ῡ for the spontaneous fission of Cf252. This reference value is taken to be ῡ = 3.80. The measurements have been performed with large liquid scintillators and the results obtained are ῡ (U238) = 1.97 ± 0.07 and ῡSD (Pu240) = 2.154 ± 0.028.