Neutron-induced fission: properties of prompt neutron andγrays as a function of incident energy

Abstract

Abstract. We have applied the Hauser-Feshbach statistical theory, in a Monte-Carlo implementation, to the de-excitation of fission fragments, obtaining a reasonable description of the characteristics of neutrons and gamma rays emitted before beta decays toward stability. Originally implemented for the spontaneous fission of 252 Cf and the neutroninduced fission of 235 U and 239 Pu at thermal neutron energy, in this contribution we discuss the extension of the formalism to incident neutron energies up to 20 MeV. For the emission of pre-fission neutrons, at incident energies beyond second-chance fission, we take into account both the pre-equilibrium and statistical pre-fission components. Phenomenological parameterizations of mass, charge and TKE yields are used to obtain the initial conditions for the fission fragments that subsequently decay via neutron and γ emissions. We illustrate this approach for 239 Pu(n,f).

Anisotropy in fission fragment and prompt neutron angular distributions

“…The required inputs are scission-fragment yields in mass, charge, total kinetic energy, spin, and parity, Y(A, Z, T KE, J, ⇡). The mass yields, Y(A), are three-Gaussian fits to experimental data [32,33], and the charge yields, Y(Z|A), are taken from Wahl systematics [34]. The TKE distribution for each mass, Y(T KE|A), is also taken to be Gaussian.…”

Angular Momentum of Fission Fragments from Microscopic Theory

“…Therefore, it is important to have a robust microscopic framework for calculating AM of FFs over a wide range of fragment masses. However, such a framework is currently missing, and the most widely used fission reaction models at the moment rely on AM distributions that are obtained from either statistical or semi-classical methods [10][11][12][13][14][15].…”

Prompt fission neutron and γ ray properties as a function of incident neutron energy

“…1(b) in Ref. [5]). However, in order to more realistically reproduce the neutron multiplicity distribution at low energies, all the values of σ TKE (A; E n ) have been reduced by 20 to 25% from the experimental values reported in the literature, depending on the reaction.…”

“…More detailed discussions can be found in Ref. [5], and in another paper currently in preparation. Inspired by the neck rupture model [6], we assume that the mass yields are given as a superposition of three fission modes (two asymmetric and one symmetric), each fission mode being characterized by Gaussian with an average mass and width.…”

“…1(a) in Ref. [5]), as a first-order approximation, that most of the energy dependence of TKE(A; E n ) can be encoded in the energy dependence of TKE for the reaction, which is mathematically equivalent to a factorization…”