Anomalies in the Charge Yields of Fission Fragments from the $^{238}$U(n,f) Reaction

J.N. Wilson (1) , M. Lebois (1) , L. Qi (1) , P. Amador-Celdran , D. Bleuel , J.A. Briz (2) , R. Carroll , W. Catford , H. de Witte , D.T. Doherty (3) , R. Eloirdi , G. Georgiev (4) , A. Gottardo (1) , A. Goasduff (4) , K. Hadyńska-Klęk , K. Hauschild (4) , H. Hess , V. Ingeberg , T. Konstantinopoulos (4) , J. Ljungvall (4) , A. Lopez-Martens (4) , G. Lorusso , R. Lozeva (4) , R. Lutter , P. Marini (5) , I. Matea (1) , T. Materna (3) , L. Mathieu (6) , A. Oberstedt , S. Oberstedt , S. Panebianco (3) , Zs. Podolyák , Amanda Porta (2) , P.H. Regan , P. Reiter , K. Rezynkina , S.J. Rose , E. Sahin , M. Seidlitz , O. Serot (7) , R. Shearman , B. Siebeck , S. Siem , A.G. Smith , G.M. Tveten , D. Verney (1) , N. Warr , F. Zeiser , M. Zielinska (3)

1 IPNO - Institut de Physique Nucléaire d'Orsay
2 SUBATECH - Laboratoire de physique subatomique et des technologies associées
3 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
4 CSNSM - Centre de Sciences Nucléaires et de Sciences de la Matière
5 DAM - Direction des Applications Militaires
6 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
7 CEA Cadarache

Fast-neutron-induced fission of $^{238}$U at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency $\gamma$-ray spectrometer (MINIBALL) to an inverse-kinematics neutron source (LICORNE) to extract charge yields of fission fragments via $\gamma$-$\gamma$ coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fast-neutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

J.N. Wilson, M. Lebois, L. Qi, P. Amador-Celdran, D. Bleuel, et al.. Anomalies in the Charge Yields of Fission Fragments from the $^{238}$U(n,f) Reaction. Physical Review Letters, 2017, 118 (22), pp.222501. ⟨10.1103/PhysRevLett.118.222501⟩. ⟨hal-01554873⟩