Multiplicity of prompt fission neutron in the ²³⁹Pu(n,f) reaction and its energy dependence

¹ LP2I Bordeaux, UMR5797, Université de Bordeaux, CNRS, F-33170 Gradignan, France
² CEA, DAM, DIF, F-91297 Arpajon, France
³ Université Paris-Saclay, CEA, LMCE, 91680 Bruyères-le-Châtel, France
⁴ Los Alamos National Laboratory, Los Alamos, NM-87545, USA
⁵ Normandie Univ, ENSICAEN, UNICAEN, CNRS/IN2P3, LPC Caen, 14000

^* e-mail: paola.marini@cnrs.fr

Published online: 17 April 2024

Abstract

Accurate multiplicities of prompt fission neutrons emitted in neutron-induced fission on a large energy range are essential for fundamental and applied nuclear physics. Measuring them to high precision for radioactive fissioning nuclides is, however, an experimental challenge. In this work, we extract the average prompt-neutron multiplicity emitted in the ²³⁹ Pu (n, f) reaction as a function of the incident-neutron energy, over the range 0.7-700 MeV. We used a novel technique, which allowed us to minimize and correct for the main sources of bias and thus achieve unprecedented precision. At low energies, our data validate, for the first time, the ENDF/B-VIII.0 nuclear data evaluation with an independent measurement and reduce the evaluated uncertainty by up to 60%. This work opens up the possibility of measuring, with high precision, prompt fission neutron multiplicities on highly radioactive nuclei relevant for energy production.