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ANITA neutron source

ANITA neutron source. Monte Carlo simulations and comparison with experimental data. Mitja Majerle Nuclear Physics Institute Řež near Prague. Outline. Summary of experimental data from June ‘08 Simulations - FLUKA: Geometry General properties, neutron fluences, EXP/SIM protons

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ANITA neutron source

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  1. ANITA neutron source Monte Carlo simulations and comparison with experimental data Mitja Majerle Nuclear Physics Institute Řež near Prague ANITA workshop, Uppsala, december 2008

  2. Outline • Summary of experimental data from June ‘08 • Simulations - FLUKA: • Geometry • General properties, neutron fluences, • EXP/SIM protons • Simulations – MCNPX • Conclusion ANITA workshop, Uppsala, december 2008

  3. Experimental data user1 cross of detectors + Cu detector user2, user3 positions (6m, 12m) • Activation detectors at user1-user3 • Data presented at EFNUDAT meeting: • Uniform beam • LE neutrons from background • Protons not detected • Detectable limit for neutrons reached at user2 and user3 collimator for LE neutrons concrete wall ANITA workshop, Uppsala, december 2008

  4. Monte Carlo simulations • FLUKA • PEANUT spallation model • ENDF library up to 20 MeV • MCNPX • Bertini/Dresner, CEM, INCL/ABLA spallation models • LA150, NRG2003, TENDL libraries up to 150 MeV • Setup description from schematic drawings (beam at 3 deg right, y=-3mm), magnetic field 0.15 T ANITA workshop, Uppsala, december 2008

  5. Simulated quantities • Neutron and proton flux in 3 planar cross-sections: • XZ around target • XY before collimator • XY behind collimator • Neutron and proton spectral fluences: • 10x10 cm2 before collimator – “user0” • 2x2 cm2 in user1-user3 ANITA workshop, Uppsala, december 2008

  6. XZ around target Neutron flux in XZ Proton flux in XZ FLUKA simulations ANITA workshop, Uppsala, december 2008

  7. XY before collimator Proton flux in XY Neutron flux in XY Protons at 1T magnetic field FLUKA simulations ANITA workshop, Uppsala, december 2008

  8. XY after collimator Neutron flux in XY Proton flux in XY FLUKA simulations ANITA workshop, Uppsala, december 2008

  9. Spectral fluences • 3*1010 histories • Detector 2x2 cm2 positioned 250 cm from the target – user1 • Neutrons: • 100 log bins (4 keV..20 MeV) • 160 bins (20..180 MeV) • Protons: • 180 bins (0..180 MeV) • Proton spectrum sampled at user0 multiplied with k=user1/user0 to get better statistics FLUKA simulations ANITA workshop, Uppsala, december 2008

  10. Activation detectors • Neutron spectral fluence is folded with cross sections (TALYS 1.0 + correction to better fit EXFOR data) • Isotopes: • 7xAu • 2xAl • 6xBi • 5xTa • 3xCu • Uncertainties: • 10-15% spectroscopy • ~2% statistical (simulation) • ~ 10% and more TALYS cross sections ANITA workshop, Uppsala, december 2008

  11. Experiment / calculation FLUKA simulations ANITA workshop, Uppsala, december 2008

  12. Protons in the beam • Proton background in simulation is suppressed for a factor of 1300 • 1300=(number of neutrons/number of protons) in energy range 1-200 MeV • This is 40x lower than the detection limit of used activation detectors – 63Cu(p,n)63Zn • 40=(the smallest mass of Zn that could be detected with 98% accuracy)/(simulated mass of Zn) • Only from experiment we can say that protons are suppressed at least for a factor of 30 (with 98% probability, vs. neutrons) ANITA workshop, Uppsala, december 2008

  13. MCNPX • The same geometry and materials as in FLUKA was implemented in MCNPX • MCNPX has no possibility to simulate magnetic field (which has negligible influence anyway) • 3 cascade models were tested: • Bertini • CEM • INCL/ABLA • 5*108 histories, slower simulations ANITA workshop, Uppsala, december 2008

  14. 2D distributions Neutrons and protons in XZ around the target Neutrons in XY before and after iron wall ANITA workshop, Uppsala, december 2008 MCNPX simulations

  15. Neutron spectral fluences • Spectra calculated with MCNPX are similar to FLUKA spectra at first look • Differences in 20-150 MeV region are up to 50%, MCNPX is systematically lower (libs, geometry?) • Can experiment determine the best spectrum ? • Activation detectors themselves have ca. 50% spread ANITA workshop, Uppsala, december 2008

  16. EXP/SIM for MCNPX MCNPX simulation, BERTINI/DRESNER Average EXP/SIM ~ 1.5 MCNPX simulation, CEM Average EXP/SIM ~ 1.6 ANITA workshop, Uppsala, december 2008

  17. Conclusion • Accurate simulations confirmed our experimental conclusions: uniform beam, no protons. • EXP/SIM for activation detectors is ca. 1, with the spread ca. 50%. • Spectra calculated with different models differ for 50%. • All presented data are available at: http://ojs.ujf.cas.cz/~mitja/download/uppsala The access to the METACentrum computing facilities provided under the research intent MSM6383917201 is appreciated. ANITA workshop, Uppsala, december 2008

  18. XY before collimator at 1T magnetic field Neutron flux in XY Proton flux in XY FLUKA simulations ANITA workshop, Uppsala, december 2008

  19. 25 keV peak 56Fe(n,TOT) cross sections from ENDF ANITA workshop, Uppsala, december 2008

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