Fission modelling with FIFRELIN

Abstract

The nuclear fission process gives rise to the formation of fission fragments and emission of particles (n, γ, e −). The particle emission from fragments can be prompt and delayed. We present here the methods used in the FIFRELIN code, which simulates the prompt component of the de-excitation process. The methods are based on phenomenological models associated with macroscopic and/or microscopic ingredients. Input data can be provided by experiment as well as by theory. The fission fragment deexcitation can be performed within Weisskopf (uncoupled neutron and gamma emission) or a Hauser-Feshbach (coupled neutron/gamma emission) statistical theory. We usually consider five free parameters that cannot be provided by theory or experiments in order to describe the initial distributions required by the code. In a first step this set of parameters is chosen to reproduce a very limited set of target observables. In a second step we can increase the statistics to predict all other fission observables such as prompt neutron, gamma and conversion electron spectra but also their distributions as a function of any kind of parameters such as, for instance, the neutron, gamma and electron number distributions, the average prompt neutron multiplicity as a function of fission fragment mass, charge or kinetic energy, and so on. Several results related to different fissioning systems are presented in this work. The goal in the next decade will be i) to replace some macroscopic ingredients or phenomenological models by microscopic calculations when available and reliable, ii) to be a support for experimentalists in the design of detection systems or in the prediction of necessary beam time or count rates with associated statistics when measuring fragments and emitted particle in coincidence iii) extend the model to be able to run a calculation when no experimental input data are available, iv) account for multiple chance fission and gamma emission before fission, v) account for the scission neutrons. Several efforts have already been made to replace macroscopic ingredients and phenomenology by microscopic ingredients provided in various nuclear parameter libraries such as electric dipole photon strength functions or HFB level densities. First results relative to theses aspects are presented in this work.

C-BORD project: “Effective container inspection at BORDer control points”

“…Due to experimental difficulties to have a clear signal in such a γ -background, studied nuclei only concerned the long living ones (T 1 2 > minute). From the theoritical point of view, Monte Carlo simulation for particle emissions in fission codes have been developed, such as CGMF [14], FREYA [15], FIFRELIN [16]. These new developments bring complementary informations concerning the fission process and nuclear data of prompt neutron and gamma, but do not reproduce all of the experimental results and are still being ameliorated.…”

“…3, it seems that in the spontaneous fission process of 252 Cf, an important part of 134 Te is produced after neutron emission, below the 6 + (at 1.691 MeV, T 1 2 = 164 ns) isomeric level (on the 4 + , 2 + or 0 + state). We compared experimental results with the fission modelling calculation code FIFRELIN [16]. The calculations of the spontaneous fission of 252 Cf were performed by O. Litaize (CEA, Cadarache, France).…”

Theoretical investigation of fission fragment kinetic energy distributions in the symmetric mass region for233U(nth,f)

“…FIFRELIN is a Monte Carlo code developed at CEA Cadarache [3][4][5]. This code aims to describe the de-excitation path of a fission fragment since its creation until reaching a nuclear state leading to a β decay of the atomic nucleus.…”

“…Section 2 presents briefly the experimental apparatus as well as methodology and results. The interpretation of these data was done by combining the fission channels predicted by Brosa [2] with the Monte Carlo code FIFRELIN [3][4][5]. In order to compare these simulated data with experimental data, energy loss corrections must be applied.…”

Prompt neutron emission and energy balance in 235U(n,f)

“…Efforts to calculate PFN and fragment correlations using Monte-Carlo technique have been quite successful in reproducing available experimental data [6][7][8]. However, a e-mail: alf.gook@ec.europa.eu in the case of 235 U(n,f) difficulties have been encountered [8], especially regarding the dependency of ν on the fragment TKE.…”