Measurement of the 235 U(n,f) cross section at n_TOF from thermal to 170 keV

Simone Amaducci , O. Aberle , J. Andrzejewski , L. Audouin (1) , M. Bacak (2) , J. Balibrea , M. Barbagallo , F. Bečvář , E. Berthoumieux (2) , J. Billowes , D. Bosnar , A. Brown , M. Caamaño , F. Calviño , M. Calviani , D. Cano-Ott , R. Cardella , A. Casanovas , F. Cerutti , Y.H. Chen (1) , E. Chiaveri , N. Colonna , G. Cortés , M.A. Cortés-Giraldo , L. Cosentino , L.A. Damone , M. Diakaki (2) , C. Domingo-Pardo , R. Dressler , E. Dupont (2) , I. Durán , B. Fernández-Domínguez , A. Ferrari , P. Ferreira , P. Finocchiaro , V. Furman , K. Göbel , A.R. García , A. Gawlik , S. Gilardoni , T. Glodariu , I.F. Gonçalves , E. González-Romero , E. Griesmayer , C. Guerrero , F. Gunsing (2) , H. Harada , S. Heinitz , J. Heyse , D.G. Jenkins , E. Jericha , F. Käppeler , Y. Kadi , A. Kalamara , P. Kavrigin , A. Kimura , N. Kivel , I. Knapova , M. Kokkoris , M. Krtička , D. Kurtulgil , S. Lo Meo , E. Leal-Cidoncha , C. Lederer , H. Leeb , J. Lerendegui-Marco , S.J. Lonsdale , D. Macina , A. Manna , J. Marganiec , T. Martínez , A. Masi , C. Massimi , P. Mastinu , M. Mastromarco , E.A. Maugeri , A. Mazzone , E. Mendoza , A. Mengoni , P.M. Milazzo , F. Mingrone , A. Musumarra , A. Negret , R. Nolte , A. Oprea , N. Patronis , A. Pavlik , J. Perkowski , I. Porras , J. Praena , J.M. Quesada , D. Radeck , T. Rauscher , R. Reifarth , C. Rubbia , J.A. Ryan , M. Sabaté-Gilarte , A. Saxena , P. Schillebeeckx , D. Schumann , P. Sedyshev , A.G. Smith , N.V. Sosnin , A. Stamatopoulos , G. Tagliente , J.L. Tain , A. Tarifeño-Saldivia , L. Tassan-Got (1) , S. Valenta , G. Vannini , V. Variale , P. Vaz , A. Ventura , V. Vlachoudis , R. Vlastou , A. Wallner , S. Warren , C. Weiss , P.J. Woods , T. Wright , P. Žugec

1 IPNO - Institut de Physique Nucléaire d'Orsay
2 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers

The $^{235}$U(n,f) cross section plays a key role for nuclear physics due to its widespread use as a standard reference for neutron cross section measurements and for neutron flux measurements. Recent experimental data of the fission cross section have suggested the presence of discrepancies around 6–8% with respect to the most used libraries, precisely in the range between 10 keV and 30 keV. In order to shed light on this disagreement, an accurate measurement of the $^{235}$U(n,f) fission cross section has been performed at n_TOF facility @CERN, using the standard reactions $^{6}$Li(n,t) and $^+{10}$B(n,α) as reference. A custom experimental setup based on a stack of silicon detectors sandwiched between pairs of $^{235}$U, $^{6}$Li and $^{10}$B targets, has been installed along the neutron beam line to intercept the same neutron flux, allowing the detection of the fission fragments and the products of the reference reactions at the same time. Such a technique allows calculation of the cross section via the “ratio method”, by normalizing the $^{235}$U(n,f) reaction yields with respect to the reference reactions and to the recommended data in the IAEA libraries; in particular, the integral between 7.8 and 11 eV has been chosen. Accurate Monte Carlo simulations have allowed evaluation of the neutron absorption in the different layers, as well as the detection efficiency of each detector. The data are in excellent agreement with the standard values and highlight the overestimation of the $^{235}$U(n,f) cross section between 9 and 18 keV in the most recent libraries.

Mots clés: Standard; cross-section; neutrons; uranium; fission; n_TOF

Domaines: Physique [physics]

Simone Amaducci, O. Aberle, J. Andrzejewski, L. Audouin, M. Bacak, et al.. Measurement of the 235 U(n,f) cross section at n_TOF from thermal to 170 keV. The 2019 International Conference on Applications of Nuclear Techniques, Jun 2019, Rithymna Beach, Greece. pp.2060011, ⟨10.1142/S2010194520600113⟩. ⟨hal-02966268⟩