Event-by-event Neutron-Photon Multiplicity Correlations In 242Pu(sf)

We have analyzed the emission of neutrons and gamma rays by a spontaneously fissioning source of 242Pu(sf). Fission events were separated from decays using an ionization chamber, which provided clear separation between decay modes as well as a precise timing for the fission event. We have performed the experiment at the Los Alamos Neutron Science Center (LANSCE), using the Chi-Nu array. The 54 organic scintillation detectors of Chi-Nu are suitable for both neutron and gamma-ray detection and provide an excellent system for the study of neutron-photon correlations accompanying fissions. In this paper we present the results of our investigation of neutron-photon correlations in the form of neutron-photon multiplicity covariance. We determine and unfold this parameter for the 242Pu(sf) reaction and compare it with the analogous result from 252Cf(sf). Our preliminary results show that the covariance is comparable in magnitude to the 252Cf(sf) results, indicating that the correlations are not proportional to the neutron multiplicity or initial excitation energy. This result is explained physically by considering the negative correlations as predominantly existing for the last neutrons and the first photons in the emission cascade.