Energy correlations of prompt fission neutrons in the laboratory frame

Correlations between the energies and emission angles of prompt fission neutrons are of significance for all methods which use the statistics of detection events for determining subcritical reactivity in reactor cores or for non-destructive assay of nuclear materials for safeguards purposes. There is no experimental knowledge available on the existence or properties of such correlations. Therefore, recently increasing attempts are made to determine these correlations from the properties of the fission process. One possible reason of such correlations between fission neutron energies and angles in the laboratory system is the fact that the prompt neutrons are emitted from the moving fission targets, even if their energies and emission angles are independent in the moving frame of the fission fragment. In this paper this concept is investigated analytically and through numerical simulations. It is shown that such correlations are due to the random properties (energy and direction of motion) of the fission fragments, and the magnitude of the covariance depends on the second order moments of the fission fragment parameters. Preliminary numerical simulations show that the correlations in energy, generated this way, are rather small