Abstract
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).
Highlights
In recent years the measurement of prompt fission γ ray spectra (PFGS) has undergone a renaissance, motivated by requests for new precise values especially for γ -ray multiplicities and average photon energy release per fission in the thermal-neutron-induced fission of 235U [1] and 239Pu [2]
In this paper we present first results for prompt fission γ -ray spectra (PFGS) characteristics from the spontaneous fission of 240Pu and 242Pu
The results are an average energy per photon γ = (0.80 ± 0.07) MeV, the average multiplicity Mγ = (8.2 ± 0.4), and an average total γ -ray energy release per fission Eγ,tot = (6.6 ± 0.5) MeV
Summary
In recent years the measurement of prompt fission γ ray spectra (PFGS) has undergone a renaissance, motivated by requests for new precise values especially for γ -ray multiplicities and average photon energy release per fission in the thermal-neutron-induced fission of 235U [1] and 239Pu [2]. Improvements of nuclear data have become possible due to advances in scintillator materials as used, e.g., in lanthanide halide detectors They offer a superior combination of intrinsic peak efficiency, energy, and timing resolution, as already demonstrated in a number of recent experiments on 252Cf(sf) [3,4,5], 235U(nth,f ) [4,6], and 241Pu(nth,f ) [4,7]. This campaign is motivated by the first parametrization to describe systematic trends of PFGS characteristics which was made by Valentine [8] He introduced a somewhat arbitrary functional dependence of PFGS characteristics on the compound nucleus (CN) mass and atomic numbers as well as its prompt fission neutron multiplicity, accounting for the competition between the two deexcitation channels of prompt γ -ray and neutron emission. Published experimental results as shown in Refs. [9,10], more data are necessary in order to reduce the statistical uncertainties on the model parameters
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