Prompt fission gamma-ray spectrum characteristics from Pu-240(sf) and Pu-242(sf)

In this paper we present first results for prompt fission gamma-ray spectra (PFGS) characteristics from the spontaneous fission (sf) of Pu-240 and Pu-242. For Pu-242(sf) we obtained, after proper unfolding of the detector response, an average energy per photon (epsilon) over bar (gamma) = (0.843 +/- 0.012) MeV, an average multiplicity (M) over bar (gamma) = (6.72 +/- 0.07), and an average total gamma-ray energy release per fission (E) over bar (gamma,tot) = (5.66 +/- 0.06) MeV. The Pu-240(sf) emission spectrum was obtained by applying a so-called detector-response transformation function determined from the Pu-242 spectrum measured in exactly the same geometry. The results are an average energy per photon (epsilon) over bar = (0.80 +/- 0.07) MeV, the average multiplicity (M) over bar (gamma) = (8.2 +/- 0.4), and an average total gamma-ray energy release per fission (E) over bar (gamma,tot) = (6.6 +/- 0.5) MeV. The PFGS characteristics for Pu-242(sf) are in very good agreement with those from thermal-neutron-induced fission on Pu-241 and scales well with the corresponding prompt neutron multiplicity. Our results in the case of Pu-240(sf), although drawn from a limited number of events, show a significantly enhanced average multiplicity and average total energy, but may be understood from a different fragment yield distribution in Pu-240(sf) compared to that of Pu-242(sf)