Measurement of the $^{235}$U(n,f) cross section relative to the $^6$Li(n,t) and 10B(n,$\alpha$) standards from thermal to 170 keV neutron energy range at n_TOF

S. Amaducci , L. Cosentino , M. Barbagallo , N. Colonna , A. Mengoni , C. Massimi , S. Lo Meo , P. Finocchiaro , O. Aberle , J. Andrzejewski , L. Audouin (1) , M. Bacak (2) , J. Balibrea , 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 , G. Cortés , M.A. Cortés-Giraldo , L.A. Damone , M. Diakaki (2) , C. Domingo-Pardo , R. Dressler , E. Dupont (2) , I. Durán , B. Fernández Domínguez , A. Ferrari , P. Ferreira , 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 , E. Leal-Cidoncha , C. Lederer , H. Leeb , J. Lerendegui-Marco , S.J. Lonsdale , D. Macina , A. Manna , J. Marganiec , T. Martínez , A. Masi , P. Mastinu , M. Mastromarco , E.A. Maugeri , A. Mazzone , E. Mendoza , 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 was measured at n_TOF relative to$^{6}$Li(n, t) and$^{10}$B(n, $ \alpha$ ) , with high resolution ( $ L=183.49(2)$ m) and in a wide energy range (25meV-170keV) with 1.5% systematic uncertainty, making use of a stack of six samples and six silicon detectors placed in the neutron beam. This allowed us to make a direct comparison of the yields of the$^{235}$U(n, f ) and of the two reference reactions under the same experimental conditions, and taking into account the forward/backward emission asymmetry. A hint of an anomaly in the 10-30keV neutron energy range had been previously observed in other experiments, indicating a cross section systematically lower by several percent relative to major evaluations. The present results indicate that the cross section in the 9-18keV neutron energy range is indeed overestimated by almost 5% in the recently released evaluated data files ENDF/B-VIII.0 and JEFF3.3, as a consequence of a 7% overestimate in a single GMA node in the IAEA reference file. Furthermore, these new high-resolution data confirm the existence of resonance-like structures in the keV neutron energy region. The results here reported may lead to a reduction of the uncertainty in the 1-100keV neutron energy region. Finally, from the present data, a value of $ 249.7\pm 1.4(\mathrm{stat}) \pm 0.94(\mathrm{syst})$ b·eV has been extracted for the cross section integral between 7.8 and 11eV, confirming the value of $ 247.5\pm 3$ b·eV recently established as a standard.

Mots clés: n: energy; n: beam; emission: asymmetry; semiconductor detector; time-of-flight; resolution; thermal; on-line; experimental methods

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique des Hautes Energies - Expérience [hep-ex]

S. Amaducci, L. Cosentino, M. Barbagallo, N. Colonna, A. Mengoni, et al.. Measurement of the $^{235}$U(n,f) cross section relative to the $^6$Li(n,t) and 10B(n,$\alpha$) standards from thermal to 170 keV neutron energy range at n_TOF. Eur.Phys.J.A, 2019, 55 (7), pp.120. ⟨10.1140/epja/i2019-12802-7⟩. ⟨hal-02074657⟩