Total kinetic energy and mass yields from the fast neutron-induced fission of $$^{239}\hbox {Pu}$$
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Regular Article - Experimental Physics
Total kinetic energy and mass yields from the fast neutron-induced fission of 239 Pu Alexander Chemey1, Ashley Pica1, Liangyu Yao1, Walter Loveland1,a , Hye Young Lee2 , S. A. Kuvin2 1 2
Department of Chemistry, Oregon State University, Corvallis, OR, USA P-27, Physics Division, Los Alamos National Lab, Los Alamos, NM, USA
Received: 18 September 2020 / Accepted: 18 October 2020 © Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Communicated by Robert Janssens
Abstract The total kinetic energy (TKE) release in fission is an important observable, constituting over 80% of the energy released in fission (E f ≈ 200 MeV). While the TKE release in the 239 Pu(n,f) reaction was previously measured up to 50 MeV incident neutron energy (En ), there were features in TKE release at the highest values of En that were puzzling. There was a marked flattening of TKE release from En = 30 to 50 MeV, in disagreement with the clearly decreasing TKE observed from En = 0.5 to 30 MeV. To verify and clarify this trend, TKE measurements at higher values of En were made. We present absolute measurements of TKE release in 239 Pu(n,f) from En = 2.4 to 100 MeV. We used silicon PIN detectors to measure the fragment energies and deduce mass-yield curves using the 2E-method. We also discuss fission asymmetry and the relationships between approximate fission fragment mass and distortion.
1 Introduction Since the discovery of nuclear fission, and the great quantities of energy released in fission, the nature of the fission process and the division of its energy has been of great interest. It was determined that over 80% of the ∼ 200 MeV energy release is in the form of fission fragment kinetic energy, while the remainder is divided between prompt gamma rays, neutrons, and radioactive decay of fission products [1–4]. Resultingly the TKE is an important feature in understanding the fission process. This manuscript will refer to fission products and fission fragments separately, where fission fragments are the Electronic supplementary material The online version of this article (https://doi.org/10.1140/epja/s10050-020-00295-6) contains supplementary material, which is available to authorized users. a e-mail:
[email protected] (corresponding author)
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nuclei prior to prompt neutron emission and those immediately after as fission products [5]. 1.1 Energy release in fission The total energy released in fission (E f ) is easily calculated from the excitation of the compound nucleus and the mass excesses of fission fragments, when they are known. This energy is released in several forms, and can be described as E f = T K E + E p f + Ed
(1)
where E p f is the energy released in prompt deexcitation, and Ed is the energy released by fission product daughter nuclides due to de- excitation/relaxation, particle evaporation, and subsequent decay [1,6]. The sum of E p f and Ed are therefore summarized as the excess energy available above the potential
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