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First results of the neutron induced fission cross section measurement of Uranium-236 at n_TOF facility
Z. Eleme1, A. Tsinganis2, M. Patronis1, M. Bacak3, N. Colonna4, M. Diakaki5, P. Dimitriou6, V. Foteinou1,S. Goula1,7, J. Heyse2, M. Kokkoris5, N. Kyritsis5, V. Michalopoulou5, A. Musumarra8, D. Papanikolaou8, M.G. Pellegriti8, M. Peoviti1, M.E. Stamati1,7, P. Schillebeeckx2, G. Tagliente4, R. Vlastou5 and the n_TOF Collaboration
1 University of Ioannina, Ioannina, Greece
2 European Commission, Joint Research Centre (JRC), Geel, Belgium
3 University of Vienna, Faculty of Physics, Vienna, Austria
4 Instituto Nazionale di Fisica Nucleare, Sezione di Bari, Italy
5 National Technical University of Athens, Athens, Greece
6 International Atomic Energy Agency (IAEA), Vienna, Austria
7 European Organization for Nuclear Research (CERN), Switzerland
8 Instituto Nazionale di Fisica Nucleare, Sezione di Catania, Italy
High-accuracy cross section data for neutron induced reactions are essential over a wide energy range to support the design, feasibility and sensitivity studies on advanced nuclear systems [1, 2]. 236U (T1/2= 2.342x107 years) is a long-lived isotope with high specific activity, making it a major contributor to the radioactivity of reprocessed uranium. In U/Pu reactors 236U is produced through neutron capture on 235U, affecting both the neutron balance and fuel composition, while it also accumulates in the Th/U fuel cycle. Therefore, accurate knowledge of its fission cross section, within 5%, is required for the development of fast nuclear reactors and accelerator-driven-systems (ADS) [3].
For the 236U(n,f) reaction cross section, evaluated nuclear data libraries show large discrepancies in the thermal neutron region, reaching up to two orders of magnitude. Among them, only JENDL-5 [4] and JEFF-4.0 [5] reasonably reproduce the limited experimental data reported by Wagemans et al. [6,7]. Above 500 keV, existing measurements differ by up to 15%, while beyond 40 MeV only three data sets extend to several hundred MeV [8–10]. This high energy region is particularly important for constraining theoretical models of the fission process.
In this work, the 236U(n,f) cross section was measured at the n_TOF facility at CERN using Micromegas detectors and the time-of-flight technique. For the measurement, two high-purity 236U samples were employed, together with 235U, 238U, and 10B reference samples for neutron flux monitoring [11]. This contribution provides an overview of the experimental setup and presents preliminary results covering the neutron energies from meV to 400 MeV, compared with previous measurements and evaluated nuclear data libraries.
REFERENCES
[1] A. Stanculescu, Annals of Nuclear Energy 62, 607-612 (2013)
[2] Generation-IV International Forum, www.gen-4.org/
[3] INDC International Nuclear Data Committee,Summary Report of the Consultants’
Meeting on Assessment of Nuclear Data Needs for Thorium and other Advanced Cycles, INDC(NDS)-408 (IAEA, Vienna, 1999).
[4] O. Iwamoto et al., Journal of Nuclear Science and Technology 60(1), 1-60 (2023)
[5] https://databank.io.oecd-nea.org/data/jeff/40/
[6] C. Wagemans et al., Nucl. Sci. Eng. 136, 415 (2000)
[7] C. Wagemans et al., Nucl. Sci. Eng. 160, 200 (2008)
[8] F. Tovesson et al., Nucl. Sci. Eng. 178, 57 (2014)
[9] Z. Ren et al., Eur. Phys. J. A 59, 5 (2023)
[10] A. S. Vorobyev et al., Phys. Rev. C 108, 014621 (2023)
[11] Z. Eleme et al., CERN-INTC-2024-029;INTC-P-700