  The emission of neutrons and gamma rays by fission fragments reveal important
information about the properties of fragments immediately following scission.
The initial fragment properties, correlations between fragments, and emission
competition give rise to correlations in neutron-gamma emission. Neutron-gamma
correlations are important in nonproliferation applications because the
characterization of fissionable samples relies on the identification of
signatures in the measured radiation. Furthermore, recent theoretical and
experimental advances have proposed to explain the mechanism of angular
momentum generation in fission. In this paper, we present a novel analysis
method of neutrons and gamma rays emitted by fission fragments that allows us
to discern structure in the observed correlations. We have analyzed data
collected on \ce{^{252}Cf}(sf) at the Chi-Nu array at the Los Alamos Neutron
Science Center. Through our analysis of the energy-differential neutron-gamma
multiplicity covariance, we have observed enhanced neutron-gamma correlations,
corresponding to rotational band gamma-ray transitions, at gamma-ray energies
of $0.7$ and $1.2$ MeV. To shed light on the origin of this structure, we
compare the experimental data with the predictions of three model calculations.
The origin of the observed correlation structure is understood in terms of a
positive spin-energy correlation in the generation of angular momentum in
fission.
