Abstract
In the neutron resonance range, fission cross section of 239Pu can be seen as a sum of the immediate (n,f) and the two-step (n,γf) fission reactions. In that case, five channel widths should be considered for a proper evaluation, those are: two opened fission channels for Jπ = 0+, one opened fission channel for Jπ = 1+ and two J-dependent for the (n,γf) reaction. The sizeable contribution of the (n,γf) process should have an impact on the determination of the capture and fission widths involved in the Reich-Moore approximation of the R-matrix theory. The present work aims to investigate this impact by using the CONRAD code and the Γγf available from literature. Prompt neutron multiplicity (νp) has been also reproduced including the contributions of the (n,γf) process.
Highlights
When a low-energy neutron collides with a target nucleus there is a high probability to form a compound nucleus in a given excited state
The prompt neutron multiplicity of the 239Pu(n,f) reaction has been reevaluated taking into account both, the “immediate” and the “two-step” contributions to the total fission cross section
The multiple analysis of the total and partial cross sections, and the total and prompt neutron multiplicity has been performed using the CONRAD code developed at CEA/Cadarache
Summary
When a low-energy neutron collides with a target nucleus there is a high probability to form a compound nucleus in a given excited state. This compound nucleus may decay in different manner as by neutron or γ-ray emission, or by fission. It may happen that one γ-ray is emitted before fission occurs, through a two-step fission reaction, contributing to the total fission cross section In this case, the available excitation energy to the fission fragment is lower and less prompt neutrons are emitted, leading to an anticorrelation between promptneutron emission and γ-ray emitted before fission multiplicities
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