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Spokeperson: M. Barbagallo Technical coordinator: O. Aberle

High accuracy measurement of the 235 U(n,f) reaction cross-section in the 10-30 keV neutron energy range in EAR1 @n_TOF. Spokeperson: M. Barbagallo Technical coordinator: O. Aberle CERN INTC meeting, June 25 th 2014. Why 235 U(n,f) @ 10-30 keV?.

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Spokeperson: M. Barbagallo Technical coordinator: O. Aberle

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  1. High accuracy measurement of the 235U(n,f) reaction cross-section in the 10-30 keV neutron energy range in EAR1@n_TOF Spokeperson: M. Barbagallo Technical coordinator: O. Aberle CERN INTC meeting, June 25th 2014

  2. Why 235U(n,f) @ 10-30 keV? • 235U(n,f) cross-sectionis often (i.e. nearly always) used as a reference in cross-section measurements of major and minor actinides. • 235U(n,f) based detectors are widely used to measure neutron fluxes (MACS..). • 235U(n,f) cross section in the energy range proposed can have a significant impact on fast critical reactor and sub-critical ADS. M. Barbagallo, CERN INTC meeting, June 25th 2014

  3. 6-8% overestimation of the fission cross-section of 235U in database? 235U(n,f)cross section not standard in that energy region, but declared known with <1% uncertainty (**) Motivations 1 • The n_TOF Phase-2 neutron flux was accurately determined using 5 different detectors and 3 different converting reactions. • The analysis of the neutron flux has revealed a discrepancy between results based on 235U(n,f) cross section and results based on 6Li(n,t)a and 10B(n,a)7Li, regardless of the detection system used (*). • Also the comparison with the simulations shows such a discrepancy in the range 10-30 keV. *M. Barbagallo, C. Guerrero, A. Tsinganis, D. Tarrio et al. Eur. Phys. J. A (2013) 49:156 **A.D. Carlson et al., Nucl. Data Sheet 119, 3215 (2009) M. Barbagallo, CERN INTC meeting, June 25th 2014

  4. Motivations 1 In the energy range of interest the flux was determined combining the results from SiMon and MGAS(10B) detectors. The uncertainty in the 6Li(n,t) and 10B(n,a)angular distributions and on the particles selection prevents us from drawing a conclusion on this issue. SiMon neutrons MGAS 10B neutrons Gas M. Barbagallo, CERN INTC meeting, June 25th 2014

  5. Motivations 1 In the energy range of interest the flux was determined combining the results from SiMon and MGAS(10B) detectors. The uncertainty in the 6Li(n,t) and 10B(n,a) angular distributions and on the particles selection prevents us from drawing a conclusion on this issue. SiMon MGAS(10B) A more accurate measurement is needed. M. Barbagallo, CERN INTC meeting, June 25th 2014

  6. ENDF/B-VII.1 JENDL-4.0 JEFF-3.2 Motivations 2 Evaluations in general are in agreement, although “resonance-like” structures are reported only in ENDF/B-VII.1 library. Only in this region, the uncertainties have been increased by a factor 4 in the latest release of ENDF/B-VII data library. M. Barbagallo, CERN INTC meeting, June 25th 2014

  7. Status of evaluations and experimental data M. Barbagallo, CERN INTC meeting, June 25th 2014

  8. Motivations 3 235U(n,g) cross section was recently measured at Los Alamos relative to 235U(n,f) using DANCE+PPAC The 10% difference attributed to 235U(n,g) cross section could rather be explained by the overestimation of the fissioncross section, consistent with our finding. M. Barbagallo, CERN INTC meeting, June 25th 2014

  9. EAR1@n_TOF 6Li/LiF 10B 235U neutrons Si detectors The measurement We propose to measure in EAR1 the 235U(n,f) cross section together with the reference reactions 6Li(n,t) and 10B(n,a). Silicon detectors stack (4x4 cm2 and 200-300 mm thickness) in the beam (capture collimator) • Detection at forward and backward directions • Energy resolution • No g-flash issues in the energy range of interest Detector test during the commissioning (Optimized MicroMegas) • Samples: • 200-300 mg/cm26Li(C-Li-C or LiF) (LNS) • 0.5 mm 10BC4(possibly directly on the detector or on both sides of the backing) (CERN) • 500 mg/cm2 235U (IRMM) M. Barbagallo, CERN INTC meeting, June 25th 2014

  10. Protons request In order to reach 1% accuracy in the energy range of interest and to observe resonance structures we ask for 1.5x1018protons on target • 500 mg/cm2 of 235U on 2 cm diameter circular area • Efficiency 95% • Flux= Flux@EAR1 • 1.5X1018 protons • 200 mg/cm2 of 6Li and 250 mg/cm2 of 10B4C on 2 cm diameter circular area • Efficiency 95% • Flux= Flux@EAR1 M. Barbagallo, CERN INTC meeting, June 25th 2014

  11. Thanks for your attention

  12. Back up slides

  13. Expected energy deposition 6Li 200 mg/cm26Li in C sandwich deposited on 1.5 mm Mylar backing M. Barbagallo, CERN INTC meeting, June 25th 2014

  14. Expected energy deposition 10B Alpha particles 125 mg/cm210B4C on 1.5 mm Mylar backing M. Barbagallo, CERN INTC meeting, June 25th 2014

  15. Expected energy deposition 235U 500 mg/cm2235U on 2 mm Al backing M. Barbagallo, CERN INTC meeting, June 25th 2014

  16. Bleed-trough SiMon M. Barbagallo, CERN INTC meeting, June 25th 2014

  17. Bleed-trough MGAS M. Barbagallo, CERN INTC meeting, June 25th 2014

  18. Status of evaluations and experimental data Courtesy of P.Schillebeeckx, IRMM M. Barbagallo, CERN INTC meeting, June 25th 2014

  19. Evaluated n_TOF Flux M. Barbagallo, CERN INTC meeting, June 25th 2014

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