Correlations between energy and ?-ray emission in 239Pu(n, f)

We study gamma -ray emission following 239Pu(n, f ) over an incident neutron energy range of 2 < Ei < 40 MeV. We present the first experimental evidence for positive correlations between the total angular momentum generated in fission and the excitation energy of the compound nucleus prior to fission. The gamma -ray multiplicity increases linearly with incident energy below the second-chance fission threshold with a slope of 0.085 +/- 0.010 MeV-1. This linear trend appears to hold for the average excitation energy of the compound nucleus between 9 < (Ex) < 19 MeV. Most of the multiplicity increase comes from an enhancement around a gamma -ray energy of 0.7 MeV, which we interpret as stretched quadrupole gamma rays that indicate an increase in total fission-fragment angular momentum with excitation energy.