First direct measurement of isotopic fission-fragment yields of $^{239}$U

TL;DR

This paper reports the first direct measurement of isotopic fission-fragment yields of $^{239}$U, providing valuable data to evaluate fission models relevant for advanced nuclear reactors.

Contribution

It presents the first complete experimental measurement of $^{239}$U fission fragment yields at specific excitation energies, validating and refining fission models.

Findings

Data agree with model calculations.

No anomaly in $^{239}$U fission yields.

Shell effects persist at high excitation energies.

Abstract

A direct and complete measurement of isotopic fission-fragment yields of $^{239}$U has been performed for the first time. The $^{239}$U fissioning system was produced with an average excitation energy of 8.3 MeV in one-neutron transfer reactions between a $^{238}$U beam and a $^{9}$Be target at Coulomb barrier energies. The fission fragments were detected and isotopically identified using the VAMOS++ spectrometer at the GANIL facility. This measurement allows to directly evaluate the fission models at excitation energies of fast neutrons, relevant for next-generation nuclear reactors. The present data, in agreement with model calculations, do not support the recently reported anomaly in the fission-fragment yields of $^{239}$U and confirm the persistence of spherical shell effects in the Sn region at excitation energies exceeding the fission barrier by few MeV.