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Why 235 U(n,f) @ 10-30 keV?

High accuracy measurement of the 235 U(n,f) reaction cross-section in the 10-30 keV neutron energy range in EAR1 @n_TOF. M. Barbagallo, S. Amaducci , M. Mastromarco , L. Cosentino , N. Colonna, P. Finocchiaro , C. Massimi , S. LoMeo n_TOF Italia Meeting, Perugia, February 2017.

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Why 235 U(n,f) @ 10-30 keV?

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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 M. Barbagallo, S. Amaducci, M. Mastromarco, L. Cosentino, N. Colonna, P. Finocchiaro, C. Massimi, S. LoMeo n_TOF Italia Meeting, Perugia, February 2017

  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 and S. Amaducci, n_TOF Italia Meeting, February 2017

  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 et al. Eur. Phys. J. A (2013) 49:156 M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  4. 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 and S. Amaducci, n_TOF Italia Meeting, February 2017

  5. Status of evaluations and experimental data M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  6. 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 and S. Amaducci, n_TOF Italia Meeting, February 2017

  7. The measurement We measured (Aug-Sept 2016) in EAR1 the 235U(n,f) cross section together with the reference reactions 6Li(n,t) and 10B(n,a). EAR1@n_TOF LiF 10B 235U • Detection at forward and backward directions • Energy resolution neutrons Silicon detectors stack (5x5 cm2 and 200 mm thickness) in the beam (capture collimator) Si detectors • 500 mg/cm26LiF , 50 mm Al backing(Laboratori Nazionali del Sud) • 80 nm 10BC4 , 18 mm Al backing (ESS, Linkoping- Chewbacca) • 275 mg/cm2 235U , 250 mm Al backing(Institute for Reference Materials and Measurement) M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  8. The setup M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  9. The setup Lin/Log Mesytech preamp SiMon M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  10. Results Amplitude spectra LiF LiF 10B 235U 235U 10B M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  11. Results Amplitude vs energy spectra t t a a 7Li+noise a a FF FF 7Li+noise a a M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  12. Results Including TOF2E conversion, transmission (calculated) and selection cuts: M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  13. Results LiF Forward Backward M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  14. Results 10B Forward Backward M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  15. Results 235U Forward Backward M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  16. Results 235U Forward Backward M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  17. Extra • Applying: • Non optimized reconstruction of g-flash • Cuts non optimized for En>1 MeV Fission Fragments a For future measurements we can consider this setup to measure fission up to 10 MeV (at least?) M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  18. Old conclusions: what was left to do? • Increase statistic • Refine Time of Flight to Energy calibration • Refine cuts applied and study the sensitivity of results to them • Extract the ratios of the standards M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  19. Refine TOF2E calibration Use of code SAMMY to fit low energy resonances of 235U(n,f) reaction (L found consistent with what previously estimated) M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  20. Sensitivity study • For each detector, we have chosen six more cuts with respect a reference one (for detectors 1-4) and we looked at the differences in count-rates above thresholds. Not needed for detectors equipped with 235U. • Simulate the full setup to study the effect of cuts applied . (The simulation also permits to evaluate absorption in the materials) M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  21. Sensitivity study LiF-1 M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  22. Sensitivity study LiF-1 No effects in the energy region of interest, up to 2% around 200 keV M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  23. Sensitivity study LiF-2 M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  24. Sensitivity study LiF-2 No effects in the energy region of interest, up to 0.5% at 200 keV M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  25. Sensitivity study B-1 M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  26. Sensitivity study B-1 Up to 1.5% in the energy region of interest, up to 4% around 200 keV M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  27. Sensitivity study B-2 M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  28. Sensitivity study B-2 !!! Up to 1.5% in the energy region of interest, up to 6% around 200 keV M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  29. Sensitivity study The goal is to study the effect of bleed-trough of particles trough cuts applied • Geant4 simulations of the setup: • Detectors and samples (including backings) • Gaussian profile for neutron beam (at the center of the system and shifted by few mm in xy plane) • Needs long time to accumulate enough statistic M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  30. Sensitivity study Transmission trough materials also got ‘’for free’’ M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  31. Sensitivity study M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  32. Sensitivity study M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  33. Sensitivity study M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  34. Sensitivity study M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  35. Sensitivity study Tritons, alphas and lithium nuclei being stopped in the detectors for 2.85e9 neutrons generated Li-2 Li-1 Energy deposited [eV] B-1 B-2 Neutron energy [eV] M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  36. Sensitivity study Simulated count-rates for backward and forward detection (no experimental cuts applied so far) have been compared to experimental count-rates. (including transmission) M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  37. Sensitivity study Simulated count-rates for backward and forward detection (no experimental cuts applied so far) have been compared to experimental count-rates. (including transmission) M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  38. Conclusions/What is left to do? • Proper TOF2E calibration has been applied. • Transmission trough materials has been assessed by means of simulations. • A sensitivity study of the measured count-rate to cuts applied has been performed. • Increase statistic for simulations (currently ongoing). • Apply experimental cuts to simulation to assess bleed-trough. • Extract the final ratios of the standards. • Silicon for fission in EAR1 yes we can • With the selected sets of cuts, the effect in the energy region of interest is (in the ‘’worst’’ case scenario) about 2%. • Nevertheless if ratios are desired up to few hundreds keV (this is the case), the effects of cuts applied increase up to several percentages. M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

  39. Conclusions/What is left to do? • Proper TOF2E calibration has been applied. • Transmission trough materials has been assessed by means of simulations. • A sensitivity study of the measured count-rate to cuts applied has been performed. • Increase statistic for simulations (currently ongoing). • Apply experimental cuts to simulation to assess bleed-trough. • Extract the final ratios of the standards. • Silicon for fission in EAR1 yes we can • With the selected sets of cuts, the effect in the energy region of interest is (in the ‘’worst’’ case scenario) about 2%. • Nevertheless if ratios are desired up to few hundreds keV (this is the case), the effects of cuts applied increase up to several percentages. M. Barbagallo and S. Amaducci, n_TOF Italia Meeting, February 2017

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