Physics-Based Modeling
Robert Reedy (UNM), Kyeong Kim (U. Ariz.),
and Jozef Masarik (Komensky Univ.)
• Objective: Calculate the best possible production
rates for TCNs using:
– computer codes that numerically simulate
particle production and transport
• Monte Carlo N Particle eXtended (MCNPX)
[Reedy and Kim]; GEANT & LAHET Code
System [Masarik].
– the latest measured or evaluated cross sections
• Experimental ones for proton reactions; a few
measurements or adjusted fits for neutrons.
• 6 nuclides: 10Be, 26Al, then 14C, 36Cl, 21Ne, 3He.
Numerical Simulation Codes
• MCNPX, GEANT, and LCS codes
– extensively developed for nuclear physics;
– well tested with many benchmarks;
– often used by us for extraterrestrial problems.
• Some results by us for terrestrial in situ (and
atmospheric) terrestrial cosmogenic nuclides
• Not perfectly accurate, but represent fairly well
the basic processes involved in the production
and transport of primary and secondary particles
• Need fine tuning for TCNs.
Work on Codes
• Compare codes
– Neutron fluxes
– Rates for making cosmogenic nuclides
• Fine tune parameters in codes
– Input cosmic ray spectra – deep space and
for different locations on Earth
– “Physics” packages in codes
• Test with various measurements
Code Work – Compare fluxes
• Neutron fluxes using MCNPX and LCS
MCNP/LCS_0.1~20 MeV neutron
MCNPX_fast neutron_diff. flux
MCNP/LCS_fast neutron_diff. flux
MCNPX_<1 MeV neutron
MCNPX_0.1~20 MeV neutron
MCNP/LCS_<1 MeV neutron
MCNPX proton diff. flux
MCNP/LCS proton diff. flux

2
Particle Flux (particle/cm /s)








-9
10
-7
10
-5
10
0.001
0.1
Energy (MeV)
10
1000
10
5
Code Work, GCR fluxes
• Test various galactic cosmic ray spectra
– Castagnoli & Lal (1980), Webber & Higbie
(2003), others in space and at Earth
– Compare input spectra for protons only and
both protons and alpha particles using latest
versions of MCNPX.
• Test physics parameters in the codes
– Done for 2 sets by Kim & Reedy (2004) for
spallogenic nuclides in meteorite – similar
Code Work, Input spectra
• Work by G. W. McKinney et al. (2006) for
neutron densities in the Apollo 17 drill core
Code Work, Physics Inputs
• Work by G. W. McKinney et al. (2006) for
neutron densities in the Apollo 17 drill core
Input GCR energy cutoffs
Energy cutoff vs geomagnetic latitude
16
E cutoff - South
E cutoff - North
14
12
Energy cutoff (GeV)
• 1980 vertical
cosmic ray cutoff
rigidity data were
used to then
estimate the
primary galactic
cosmic ray (GCR)
spectrum for
various
geomagnetic
latitudes for our
MCNPX
calculations. [J.
Masarik]
10
8
6
4
2
0
0
10
20
30
40
Latitude
50
60
70
80
Code Work, Terr. GCR Fluxes
• Need good GCR spectra for all locations
Neutron Flux at various geomagnetic latitudes (En<500 MeV)
1.E-02
Neutron Flux (n/cm^2/s))
1.E-02
8.E-03
6.E-03
4.E-03
Northern Hemisphere
Measured (Southern)
2.E-03
Southern Hemisphere
0.E+00
10
20
30
40
50
60
Geomagnetic Latitude (degree)
70
80
90
Code Work, Terr. GCR Fluxes
• Gordon et al. (2004) and MCNPX Calc. [Kim]
Comparsion of fast neutron flux between MCNPX (this study) and Gordon et al. 2004
1.0E+04
1.0E+03
1.0E+02
1.0E+01
1.0E+00
1.0E-01
Neutron Flux (n/cm2/s)
1.0E-02
1.0E-03
1.0E-04
1.0E-05
1.0E-06
1.0E-07
1.0E-08
1.0E-09
1.0E-10
0~0.55 km, atmosphere): no cutoff
0~0.2 cm soil (Macrease soil): no cutoff
Gordon et al.2004 (1.6~4.7 GV)
1.0E-11
0~0.55 km, atmosphere):42.4 degree
1.0E-12
0~0.2 cm soil (Macrease):42.4 degree
1.0E-13
1.0E-08
1.0E-06
1.0E-04
1.0E-02
1.0E+00
Energy (MeV)
1.0E+02
1.0E+04
1.0E+06
Code Work, Terr. GCR Fluxes
• Gordon et al. (2004) and other calculations
BASICS OF CALCULATIONS
OF PRODUCTION RATES
• Calculate fluxes (neutrons, protons) in
specified target (geometry, composition)
and incident cosmic rays.
• Calculate production rate at depth d using
target composition (i, e.g., SiO2),
calculated spectra Φ for particles (k), and
cross sections σ for target-element pair (i,j;
e.g., O to Be-10, Si to Al-26):
– Pj(d) = i Ni k ∫σjik(Ek) Φk(Ek,d) dEk
Update Cross Sections
• Evaluate measured cross sections for
proton-induced reactions
• Adjust cross sections for neutroninduced reactions
– Use any measured (n,x) cross sections
– Adjust using good CN measurements in
extraterrestrial and terrestrial samples and
artificial targets (natural & accelerators)
CROSS SECTIONS FOR PRODUCTION OF 10Be
& 26Al ON TARGET ELEMENTS BY PROTONS
26
10
Al proton cross sections
Be proton cross sections
Al
SiO
2
Si
Mg
100
1
0.1
0.01
0.001
C
O
Si
Al
Mg
0.0001
Proton cross section (mb)
Proton cross section (mb)
10
10
1
0.1
-5
10
10
100
Proton energy (MeV)
1000
1
10
100
Proton energy (MeV)
1000
NEUTRON-INDUCED
CROSS SECTIONS
• Neutrons dominate (~90-95%) TCN
production.
• Early work, still used (~20 yrs. ago!):
–Use a few measured neutron cross
sections (Ne).
–Use proton cross sections (Al-26),
–Adjust neutron cross sections to fit
ET measurements (Be-10, C-14).
Test Calculations
• For now, use existing extraterrestrial
and some terrestrial measurements
• Use new CRONUS results
• Refine codes, their inputs (physics
packages, input spectra), and
reaction cross sections
Production Rates of Cosmogenic Nuclides in Knyahinya
100
Production Rate (atoms/min/kg)
He-3
Al-26
C-14
Be-10
Be-10_MCNPX
C-14_MCNPX
Al-26_MCNPX
He-3_MCNPX
Ne-21_MCNPX
Ne-22_MCNPX
Ne-22
10
Ne-21
0
20
40
60
80
2
Depth (g/cm )
Be-10 data
C-14 data
Al-26 data
He-3 data
Ne-21 data
Ne-22 data
100
120
Preliminary rates for TCNs
• from quartz using LCS and [MCNPX]:
–Be-10: 5.7, [5.0]
–C-14: 18.7, [22.2]
–Al-26: 34.3, [36.4]
• Close to old rates from Masarik &
Reedy [1995]: 5.97, 18.6, and 36.1
Work this year
• Papers presented at AMS-10 on TCNs
– by Kim, Reedy, & Masarik
• Papers submitted to Proc. AMS-10
– Tests using neutron fluxes and Be-10
measured for many locations in southern
hemisphere by I. Graham [Kim et al.]
– Calculations for the air/ground interface
and effects of snow cover [Masarik et al.]
(see next 2 images)
Fast and thermal neutron fluxes
Changes due to water (snow)
Future Work
• More tests with GEANT (will probably drop
LCS as is incorporated in MCNPX and will
not be supported. GEANT is entirely
different code from LCS/MCNPX.
• Fine tune codes and their inputs
• Cross section work
• Comparisons to improve calculations
– Extraterrestrial and other existing data
– Terrestrial, especially using CRONUS data