ANITA neutron source

ANITA workshop, Uppsala, december 2008

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

Simulations – MCNPX Conclusion


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


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


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


XZ around target

FLUKA simulations

Neutron flux in XZ Proton flux in XZ


XY before collimator

FLUKA simulations

Protons at 1T magnetic field

Neutron flux in XY

Proton flux in XY


XY after collimator

FLUKA simulations

Neutron flux in XY Proton flux in XY


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

user1

1E-11

1E-9

1E-7

1E-5

1E-3

1E-1

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0

Energy [GeV]

flu

ence

[G

eV-1

cm

-2 p

roto

n-1

]

neutrons

protons

protons user0/user1

user1*E

1E-9

1E-8

1E-7

1E-6

1E-5

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0

Energy [GeV]

flu

ence

*E [

cm-2

pro

ton

-1]


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

(n,xn) cross-sections in Au

0

0.5

1

1.5

2

2.5

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0

Energy [MeV]

Cro

ss

se

cti

on

[b

arn

s]

n,2n

n,4n

n,6n

n,8n

user1

1E-11

1E-9

1E-7

1E-5

1E-3

1E-1

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0

Energy [GeV]

flu

ence

[G

eV-1

cm

-2 p

roto

n-1

]

neutrons

protons

protons user0/user1


0

0.5

1

1.5

2

Experiment / calculation

FLUKA simulations


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)

user1

1E-11

1E-9

1E-7

1E-5

1E-3

1E-1

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0

Energy [GeV]

fluen

ce [G

eV-1

cm

-2 p

roto

n-1

]

neutronsprotonsprotons user0/user1


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


2D distributions

MCNPX simulations

Neutrons and protons in XZ around the target

Neutrons in XY before and after iron wall


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

User0

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0

Energy [GeV]

Neu

tron

flue

nce

[GeV

-1 c

m-2

prot

on-1

]FLUKA

MCNPX INCL/ABLA

MCNPX CEM

MCNPX BERTINI/DRESNER


EXP/SIM for MCNPX

0

0.5

1

1.5

2

2.5

3

MCNPX simulation, BERTINI/DRESNER

Average EXP/SIM ~ 1.5

0

0.5

1

1.5

2

2.5

3

MCNPX simulation, CEM

Average EXP/SIM ~ 1.6


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.


XY before collimator at 1T magnetic field

FLUKA simulations

Neutron flux in XY Proton flux in XY


25 keV peak

Neutron spectral fluence*E at user1

1E-9

1E-8

1E-7

1E-6

1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0

Energy [GeV]

fluen

ce*E

[cm

-2 p

roto

n-1

]

56Fe(n,TOT) cross sections from ENDF

ANITA neutron source

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