Speaker
Description
Nucleon inelastic scattering to the continuum can be adequately described through the exciton or quantum mechanical multistep direct (MSD) and multistep compound (MSC) pre-equilibrium models, as they account not only for the high energy component of particle emission spectrum, but also it provides initial conditions of the formed Compound Nucleus (CN).
It was previously shown that an accurate description of the spin and parity distributions in the residual nucleus populated after the fast inelastic collision has a strong impact on the description of (n,n’γ) reactions [1,2]. These previous works suggested that, in some specific cases, a spin distribution given as an ad-hoc prescription, e.g.by Gruppelaar [3], to complement the exciton model is insufficient since such modeling does not conserve angular momentum and parity.
In contrast, while a fully quantum mechanical modeling of the pre-equilibrium process satisfies the conservation laws in physics, it is not always ideal for applying to nuclear energy and astrophysics because of large computing time. In this regard, the classical exciton model, which allows a quick determination of the particle emission energy spectrum, seems better suited. We propose an extended semi-classical exciton model, where the spin-parity distributions in the residual CN are constrained by microscopic approaches, would be a good pragmatic solution.
From microscopic pre-equilibrium calculations for neutron scattering up to 30 MeV on a largevariety of target nuclei, we deduce systematic formulae that can be used in conjunction with the exciton model and be easily implemented in general reaction modeling codes such as TALYS,EMPIRE, CoH3, and CCONE. These formulae are tested by looking at (n,xnγ) reactions andisomer productions, and recommendations for a future use are given.
[1] D. Dashdroj, et al.Phys. Rev. C, 75:054612 2007.
[2] M. Kerveno, et al.Phys. Rev. C, 2021 (in press).
[3] H. Gruppelaar, IAEA Advisory Group Meeting, BNL report, pp.143–160, 1983.