Upper Limit for the Time between Fission and the Emission of Neutrons

The Baker experiment to detect times of delay greater than ∼5×${10}^{-9\mathrm{}}$ sec for the emission of fission neutrons has been performed by observing the change in fission neutron counting rate when fission fragments are allowed to fly away from a neutron counter as compared to the counting rate when the fragments are kept in the vicinity of the counter. The fission neutrons were detected by observing proton recoils in a thick-paraffin-lined proportional counter. The percent of neutrons delayed by a time of at least 8×${10}^{-9\mathrm{}}$ sec was found to be (3.6±2.8) percent.