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

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

3. ANITA workshop, Uppsala, december 2008 Experimental data 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 user2, user3 positions (6m, 12m) concrete wall collimator user1 cross of detectors + Cu detector for LE neutrons

4. ANITA workshop, Uppsala, december 2008 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

5. ANITA workshop, Uppsala, december 2008 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 cm 2 before collimator – “user0”  2x2 cm 2 in user1-user3

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

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

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

9. ANITA workshop, Uppsala, december 2008 Spectral fluences 3*10 10 histories Detector 2x2 cm 2 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

10. ANITA workshop, Uppsala, december 2008 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

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

12. ANITA workshop, Uppsala, december 2008 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 – 63 Cu(p,n) 63 Zn  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)

13. ANITA workshop, Uppsala, december 2008 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*10 8 histories, slower simulations

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

15. ANITA workshop, Uppsala, december 2008 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

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

17. ANITA workshop, Uppsala, december 2008 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.

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

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