Fissionable isotope identification using the time dependence of delayed neutron emission

An examination of delayed neutron emission decay rates allows for the detection and identification of fissionable isotopes. The dependence of the decay rates on bremsstrahlung end-point energies and accelerator repetition rates was examined. Delayed neutrons emitted following photofission in a 238 U target were detected between bremsstrahlung pulses from a variable-energy linear electron accelerator. Bremsstrahlung end-point energies of 14, 16, 18, 20, and 22 MeV are used to show that the decay rates have no obvious dependence on the energy of the irradiating photons. Accelerator repetition rates of 3.75 , 7.5 , 15, 30, and 60 Hz demonstrate the expected frequency dependence of the decay rates.