Speaker
Description
Nuclear data in the different libraries (ENDF/B, JEFF, JENDL, CENDL) for the description of the outgoing particles are very often expressed as averaged distributions. This is the case, for example, of the (n,2n) reaction, for which we find only one energy distribution with a multiplicity equal to 2. The situation is quite similar for neutron capture (n,g) with an average photon number and an average energy spectrum.
Simulation and modeling of recent experiments such as STEREO require a better knowledge of the emitted particles with possible coincident events that are not accessible with the current data.
This work focuses on completing the currently available data to satisfy these new requirements.
Firstly, we determined the gamma-decay cascades of excited states reached by inelastic scattering when the photon production data is averaged in MF6 sections. Then, we wrote MF12 sections that allow us to perfectly reconstruct the correlations between the gamma rays of the cascade, and verified that both types of data yielded the same gamma production spectrum.
Secondly, we treated neutron capture, which in most cases presents a combination of a discrete and a continuous photon spectra. For this, we used RIPL-3, ENSDF, JEFF data with spin conservation assumptions to reconstruct gamma cascades for this reaction. We can compare this cascade with those obtained with PHITS in terms of gamma multiplicity and energy conservation. It was observed that the presence of a rotational band in 156 Gd, when studying 155 Gd neutron capture, results in a cascade of around 10 gammas as frequent as the cascades of 4 gammas, which are the physically allowed ones, and it was reported to the PHITS team. The multiplicity distribution was tested in other nuclei in a similar mass range and no anomalies were found. We thus obtain multiplicities that are in relatively good agreement with the multiplicity data in the evaluation files. It was also found that some discrepancies between PHITS data and ENSDF introduce biases in the simulation of (n,g) reactions.
The third reaction of interest is the (n,2n) reaction. For this, we treat neutron emission by sampling the distributions given in the evaluations and taking into account kinematic limitations: correlated emission spectra can thus be produced.
These new models are tested in the Monte Carlo codes TRIPOLI-4® and PATMOS developed at CEA.
This work is carried out in the framework of a PhD thesis.