ANITA neutron source

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ANITA neutron source

• Monte Carlo simulations and comparison with
  experimental data

Mitja Majerle Nuclear Physics Institute Rež near
Prague
2
Outline

• Summary of experimental data from June 08
• Simulations - FLUKA
• Geometry
• General properties, neutron fluences,
• EXP/SIM protons
• Simulations MCNPX
• Conclusion

3
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

user1 cross of detectors Cu detector
user2, user3 positions (6m, 12m)
collimator
concrete wall
for LE neutrons
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

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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

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XZ around target
Neutron flux in XZ
Proton flux in XZ
FLUKA simulations
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XY before collimator
Proton flux in XY
Neutron flux in XY
Protons at 1T magnetic field
FLUKA simulations
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XY after collimator
Neutron flux in XY
Proton flux in XY
FLUKA simulations
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Spectral fluences

• 31010 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
  kuser1/user0 to get better statistics

FLUKA simulations
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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

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Experiment / calculation
FLUKA simulations
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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)

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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
• 5108 histories, slower simulations

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2D distributions
Neutrons and protons in XZ around the target
Neutrons in XY before and after iron wall
MCNPX simulations
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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

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EXP/SIM for MCNPX
MCNPX simulation, BERTINI/DRESNER Average EXP/SIM
1.5
MCNPX simulation, CEM Average EXP/SIM 1.6
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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.
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XY before collimator at 1T magnetic field
Neutron flux in XY
Proton flux in XY
FLUKA simulations
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25 keV peak
56Fe(n,TOT) cross sections from ENDF