| In the fission of actinides, the nearly back-to-back motion of the fission fragments has astrong effect on the kinematics of fission neutrons. This effect is seen in the neutron-neutronopening angle distributions of correlated neutron pairs from the same fission event in which afavoring of opening angles near 0◦and 180◦is observed. As of this writing, correlated neutron-neutron opening angle distributions have been measured using neutrons from spontaneousand neutron-induced fission of actinides. This work is the first to report such a measurementusing photofission, and will provide useful experimental input for photofission models usedin codes such as MCNP and FREYA.Fission is induced using bremsstrahlung photons produced via a low duty factor, pulsed, lin-ear electron accelerator. The bremsstrahlung photon beam impinges upon a238U target thatis surrounded by a large neutron scintillation detection system capable of measuring particleposition and time of flight, from which n-n opening angle and energy are measured. Neutron-neutron angular correlations are determined by taking the ratio between a correlated neutrondistribution and an uncorrelated neutron distribution formed by the pairing of neutrons pro-duced during different beam pulses. This analysis technique greatly diminishes effects dueto detector efficiencies, acceptance, and experimental drifts.The angular correlation of neutrons from the photofission of238U shows a high dependenceon neutron energy as well as a dependence on the angle of the emitted neutrons with re-spect to the incoming photon beam. Angular correlations were also measured using neutronsfrom the spontaneous fission of252Cf, showing good agreement with past measurements. Ananomalous decline in neutron-neutron yield was observed for opening angles near 180◦.Keywords:photofission; correlated neutron emission; bremsstrahlung photons; opening an-gle |