https://doi.org/10.1140/epja/i2019-12802-7
Regular Article - Experimental Physics
Measurement of the 235U(n, f) cross section relative to the 6Li(n, t) and 10B(n,
) standards from thermal to 170 keV neutron energy range at n_TOF
1
INFN Laboratori Nazionali del Sud, Catania, Italy
2
Istituto Nazionale di Fisica Nucleare, Sezione di Bari, Bari, Italy
3
Agenzia nazionale per le nuove tecnologie (ENEA), Bologna, Italy
4
Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Bologna, Italy
5
Dipartimento di Fisica e Astronomia, Università di Bologna, Bologna, Italy
6
European Organization for Nuclear Research (CERN), Genève, Switzerland
7
University of Lodz, Lodz, Poland
8
Institut de Physique Nucléaire, CNRS-IN2P3, Univ. Paris-Sud, Université Paris-Saclay, F-91406, Orsay Cedex, France
9
Technische Universität Wien, Wien, Austria
10
CEA Irfu, Université Paris-Saclay, F-91191, Gif-sur-Yvette, France
11
Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
12
Charles University, Prague, Czech Republic
13
University of Manchester, Manchester, UK
14
Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia
15
University of York, York, UK
16
University of Santiago de Compostela, Santiago de Compostela, Spain
17
Universitat Politècnica de Catalunya, Barcelona, Spain
18
Universidad de Sevilla, Sevilla, Spain
19
Dipartimento di Fisica, Università degli Studi di Bari, Bari, Italy
20
Instituto de Física Corpuscular, CSIC - Universidad de Valencia, Valencia, Spain
21
Paul Scherrer Institut (PSI), Villingen, Switzerland
22
Instituto Superior Técnico, Lisbon, Portugal
23
Joint Institute for Nuclear Research (JINR), Dubna, Russia
24
Goethe University Frankfurt, Frankfurt, Germany
25
Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania
26
Japan Atomic Energy Agency (JAEA), Tokai-mura, Japan
27
European Commission, Joint Research Centre, Geel, Retieseweg 111, B-2440, Geel, Belgium
28
Karlsruhe Institute of Technology, Campus North, IKP, 76021, Karlsruhe, Germany
29
National Technical University of Athens, Athens, Greece
30
School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
31
Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116, Braunschweig, Germany
32
INFN Laboratori Nazionali di Legnaro, Legnaro (PD), Italy
33
Consiglio Nazionale delle Ricerche, Bari, Italy
34
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Trieste, Italy
35
Dipartimento di Fisica e Astronomia, Università di Catania, Catania, Italy
36
University of Ioannina, Ioannina, Greece
37
University of Vienna, Faculty of Physics, Vienna, Austria
38
University of Granada, Granada, Spain
39
Department of Physics, University of Basel, Basel, Switzerland
40
Centre for Astrophysics Research, University of Hertfordshire, Hatfield, UK
41
Bhabha Atomic Research Centre (BARC), Mumbai, India
42
Australian National University, Canberra, Australia
* e-mail: finocchiaro@lns.infn.it
Received:
21
March
2019
Accepted:
10
June
2019
Published online:
26
July
2019
The 235U(n, f ) cross section was measured at n_TOF relative to 6Li(n, t) and 10B(n,) , with high resolution ( 
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 235U(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 
b·eV has been extracted for the cross section integral between 7.8 and 11eV, confirming the value of 
b·eV recently established as a standard.
© The Author(s), 2019
