Low-uncertainty measurement of the 239Pu(n,f) cross section at n_TOF in a very broad energy range from 0.02 eV up to 10 MeV

The 239Pu(n,f) cross section was measured with uncertainties below 4 % from 20 meV up to 10 MeV of neutron energy at CERN’s n_TOF facility using a novel fission fragment detector with a 185.59 m flight path. Measured cross section was normalized to 1059(6) eV · b in the 9–20 eV energy range, and is consistent within uncertainties with the standard thermal value and the IAEA reference 239Pu(n,f) cross section. Experimental key values include the integral ratio I3/I1=41.20(42) defined by Duran et al. 2024 and the spectrum averaged cross section in 252Cf(sf) reference neutron field of 1802(40) mb.