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Title: Validation of MCNP6 for Electron Energy Deposition in Extended Media
Author(s): Dixon, David A.Hughes, Henry Grady III
Intended for: 2015 American Nuclear Society Winter Meeting, 2015-11-08/2015-11-12(Washington D. C., District Of Columbia, United States)
Issued: 2015-11-06
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Slide 1
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Validation of MCNP6 for Electron Energy Deposition in Extended Media
David A. Dixon and H. Grady Hughes Los Alamos National Laboratory
Slide 2
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Overview
• Introduction • Problem setup • Results • Conclusions
Slide 3
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Introduction • Gap in MCNP6 electron-photon transport V&V
– Last edep validation paper written for MCNP4C in 2003 – No validation since incorporation of new straggling logic – First step in a broader V&V effort
• Comparison to Lockwood experiments circa 1987 – 1-D single- or multi-layer semi-infinite slab – Wide range of elemental data (Z=3…79) – Source characteristics
• Monoenergetic pencil beam • Energies included: 0.1-, 0.3-, 0.5-, and 1-MeV • Angles included: 0°, 30°, and 60°
Slide 4
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Experimental Setup
Slide 5
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Simulation Characteristics • Semi-infinite slab simulation
– Subdivide into cells – Histogram results
• “Mock” simulation – closer representation of experiment – Reduces boundary crossings – Point-wise results (linear or polynomial fits)
• Study impact of – Cell size – Straggling model – ESTEP – EFAC
Slide 6
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Single-Layer Results (model/cell-size)
0.0 0.2 0.4 0.6 0.8 1.0Fraction of a Mean Range
0
1
2
3
4
5
6
Ene
rgy
Dep
osit
ion
(MeV
cm2 /
g)
Be, 0.3-MeV, ExperimentBe, 0.3-MeV, DBCN(18)=2, mockBe, 0.3-MeV, DBCN(18)=2, substeps per cell>1Be, 0.3-MeV, DBCN(18)=2, substeps per cell<1Al, 0.3-MeV, ExperimentAl, 0.3-MeV, DBCN(18)=2, mockAl, 0.3-MeV, DBCN(18)=2, substeps per cell>1Al, 0.3-MeV, DBCN(18)=2, substeps per cell<1Mo, 0.3-MeV, ExperimentMo, 0.3-MeV, DBCN(18)=2, mockMo, 0.3-MeV, DBCN(18)=2, substeps per cell>1Mo, 0.3-MeV, DBCN(18)=2, substeps per cell<1Ta, 0.3-MeV, ExperimentTa, 0.3-MeV, DBCN(18)=2, mockTa, 0.3-MeV, DBCN(18)=2, substeps per cell>1Ta, 0.3-MeV, DBCN(18)=2, substeps per cell<1
Significant overestimation
in Ta
Improved agreement for
exp. and “mock” result
Profile is slightly sensitive to substeps
per cell <1
Agreement between “mock” and histogram
results where substeps per cell > 1
Slide 7
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Single-Layer Results (Straggling)
0.0 0.2 0.4 0.6 0.8 1.0Fraction of a Mean Range
0
1
2
3
4
5
Ene
rgy
Dep
osit
ion
(MeV
cm2 /
g)
Be, 0.5-MeV, ExperimentBe, 0.5-MeV, DBCN(18)=0, mockAl, 0.5-MeV, ExperimentAl, 0.5-MeV, DBCN(18)=0, mockFe, 0.5-MeV, ExperimentFe, 0.5-MeV, DBCN(18)=0, mockCu, 0.5-MeV, ExperimentCu, 0.5-MeV, DBCN(18)=0, mockMo, 0.5-MeV, ExperimentMo, 0.5-MeV, DBCN(18)=0, mockTa, 0.5-MeV, ExperimentTa, 0.5-MeV, DBCN(18)=0, mockU, 0.5-MeV, ExperimentU, 0.5-MeV, DBCN(18)=0, mock
0.0 0.2 0.4 0.6 0.8 1.0Fraction of a Mean Range
0
1
2
3
4
5
Ene
rgy
Dep
osit
ion
(MeV
cm2 /
g)
Be, 0.5-MeV, ExperimentBe, 0.5-MeV, DBCN(18)=2, mockAl, 0.5-MeV, ExperimentAl, 0.5-MeV, DBCN(18)=2, mockFe, 0.5-MeV, ExperimentFe, 0.5-MeV, DBCN(18)=2, mockCu, 0.5-MeV, ExperimentCu, 0.5-MeV, DBCN(18)=2, mockMo, 0.5-MeV, ExperimentMo, 0.5-MeV, DBCN(18)=2, mockTa, 0.5-MeV, ExperimentTa, 0.5-MeV, DBCN(18)=2, mockU, 0.5-MeV, ExperimentU, 0.5-MeV, DBCN(18)=2, mock
Old Logic New Logic
Similar levels of agreement for different straggling models with exception of Fe, Mo, and U
Slide 8
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Single-Layer Results (ESTEP)
Results relatively insensitive to ESTEP – USE THE DEFAULTS
Slide 9
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Single-Layer Results (EFAC) • EFAC
– Controls energy grid density – E_i-1 = EFAC*(E_i) – Valid EFAC’s: 0.1-0.99 – Default is 0.92 – Increasing EFAC increases run time
Changing EFAC does not improve agreement and
increases run time – USE THE DEFAULT
Slide 10
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Multi-Layer Results Significant overestimation of EDEP after high-z-low-z
interface
Better agreement for Au-Al interface – slightly
less-disparate Zs
Boundary crossing approximations remain an
issue, but severity is problem dependent
Slide 11
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Suggestions for users • Pay attention to smallest dimensions
– Check print table 85 for estep range (need print option in input) – Divide estep range by number of substeps and compare
• Use the default – Straggling model – ESTEP – EFAC
• Bottom line – allow for margin of error – Be conservative in problems with small cells (< 1 substep) – Or for source energies below 0.3-MeV
Slide 12
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Conclusions • Confidence in integrated dose • No significant improvements in local agreement • Boundary crossings remain an issue • Similar validations indicate MCNP6 is competitive with:
– ITS (CLASS I) – PENELOPE (hybrid) – EGSnrc (hybrid) – Geant4 (hybrid)
Slide 13
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Questions?
Slide 14
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Slide 15
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Summary of Results • Energy deposition profiles
– Relatively insensitive to straggling logic – Nevertheless, there are clear benefits to new logic – Boundary crossing artifacts remain
• Total energy deposition – Generally, good agreement – 70% of results within 5% of experiment
• Overall performance satisfactory
Slide 16
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Future work • Algorithmic
– Max number of terms in multiple-scattering distributions – Boundary crossing approximation – new interpolation
• Verification and validation – Fano cavity test (in process) – Faddegon scattering experiment (in process) – Reproduce Gierga & Adams work from MCNP4 – Tabata charge deposition experiments
Slide 17
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MCNP6 Straggling Logic
Slide 18
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MCNP6 Straggling Logic
