Improvement of the accuracy of neutronics simulation of actual or future reactor designs is essential and requires a better knowledge of core neutron population. Reactor neutron population is partially driven by (n, xn) reactions that change the number and decrease the energy of the neutrons. However, the cross sections of these reactions are currently not measured with sufficient precision. This is particularly the case for the neutron inelastic scattering cross section of 238U, nucleus which represents around 90-95% of the mass of fuel in present and many future reactor core designs. It therefore features on the High Priority Request List for measurement improvement. This cross section can be measured using the prompt γ-ray spectroscopy coupled to neutron time-of-flight measurements, where the total (n, n’) cross section can be deduced from a combination of the measured (n, n’γ) partial cross sections and the level scheme information. The knowledge of the 238U level scheme is still very incomplete, inducing significant uncertainties on the resulting inelastic scattering cross section. Therefore, an effort has recently been carried out to experimentally revisit the 238U decay scheme by performing high-resolution coincidence spectroscopy of the 238U(n, n’) reaction. To obtain detailed level scheme information, the ν-Ball γ spectrometer was coupled to the LICORNE directional neutron source of the ALTO facility, allowing for the study of inelastic scattering of fast neutrons (0.5-3 MeV) on 238U via γ-γ coincidence spectroscopy. Coincidence matrices obtained during the first and the second ν-Ball campaigns were analyzed using the Radware escl8r software. 110 γ transitions and 60 levels registered in the ENSDF database have been confirmed and 158 new γ transitions and 57 new levels have been found. Although not exhaustive, the 238U level scheme information has been significantly improved and its completeness has been estimated to be up to 1.7214 MeV compared to 1.27854 MeV at present. It is hence expected to decrease the uncertainties of 238U (n, n’) cross sections, which is needed for accurate reactor core modeling.

CHATEL Carole;  WILSON J. N.;  DESSAGNE Philippe;  HENNING G.;  KERVENO Maëlle;  AGUILERA P;  ALGORA A.;  DE ANGELIS G;  BENITO J.;  BITTNER D;  BLAZHEV A.;  BOTTONI S.;  BRIZ J. A.;  CANAVAN Rhiann;  DIDIERJEAN F;  DUCHENE G;  ESMAYLZADEH A;  FISCHER J;  FORNAL B.;  FRAILE L.M.;  GAMBA E.R.;  GERST R.B.;  GLADNISHKI K.A.;  HAEFNER G.;  HAUSCHILD K.;  HEERY J;  HENRICH C.;  HIVER Corentin;  HOMM I.;  ISKRA L.W.;  JOVANCEVIC N.;  KALAYDJIEVA D;  KNAFLA L;  KNEZEVIC David;  KOCHEVA D;  KORGUL A.;  KOSIR G;  KROELL T.;  LEBOIS M.;  LEONI Silvia;  LJUNGVALL J.;  LLANOS-EXPOSITO M;  LOPEZ-MARTENS A.;  LOVSIN E;  LOZEVA R.;  MARKOVA M;  MESSINGSCHLAGER A;  MIERNIK K.;  MILANOVIC T;  MOUKADDAM M;  MURIAS J.R.;  OBERSTEDT A.;  OBERSTEDT Stephan;  PASCU S.;  PASQUALATO Giorgia;  PAULSEN W.;  PODOLYAK Zs;  POKLEPA W.;  REGAN P. H;  REZYNKINA K;  RUDIGIER Matthias;  SANCHEZ-TEMPLEQUE V;  SOLAK K.;  STOYCHEV K;  STRYJCZYK M.;  SUERDER C.;  THISSE D.;  VON TRESCKOW M;  VEDIA V.;  VESIC J;  WARR N.; 

2026-07-09

AMER PHYSICAL SOC

JRC143155

2469-9993 (online),   

https://journals.aps.org/prc/abstract/10.1103/jrh6-rh6h,    https://publications.jrc.ec.europa.eu/repository/handle/JRC143155,   

10.1103/jrh6-rh6h (online),