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Title: Correlated Neutron and Gamma-Ray Emissions in MCNP6
Author(s): Rising, Michael EvanSood, AvneetTalou, PatrickKawano, ToshihikoStetcu, Ionel
Intended for: 2014 ANS Winter Meeting and Nuclear Technology Expo,2014-11-09/2014-11-13 (Anaheim, California, United States)
Issued: 2014-12-04 (rev.1)
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2014 ANS Winter Meeting, Anaheim, CA
U N C L A S S I F I E D
Slide 1
Correlated Neutron and Gamma-ray Emissions in MCNP6
1Michael E. Rising, 1Avneet Sood, 2Patrick Talou, 2Ionel Stetcu and 2Toshihiko Kawano
1XCP-3 Division, Los Alamos National Laboratory 2T-2 Division, Los Alamos National Laboratory
ANS Winter Meeting
Anaheim, CA November 9-13, 2014
Operated by Los Alamos National Security, LLC for NNSA U N C L A S S I F I E D
2014 ANS Winter Meeting, Anaheim, CA
Outline
n Introduction
n Background
n Secondary Particle Event Generators • CGMF • FREYA
n Numerical Results • Average Quantities • Neutron and Gamma-ray Correlations
n Conclusions
n Future Work
Slide 2
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2014 ANS Winter Meeting, Anaheim, CA
Introduction
n Application of interest • Global security and nuclear nonproliferation • Detection of special nuclear material (SNM) • Warhead measurement campaign (WMC) • Passive and active interrogation techniques • Coincident neutron and photon leakage
n Key issues • Average nuclear data quantities are insufficient • Cannot predict correlated signatures of shielded SNM
n Approach to obtain predictive capability • Use transport code MCNP for modeling neutrons and photons • Need microscopic fission event information • Fission event generators are under development • Implement in MCNP and compare to experiments
Slide 3
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2014 ANS Winter Meeting, Anaheim, CA
Background
n In tabulated nuclear data libraries (i.e. ENDF/B-VII.1): • Average secondary neutron and photon information can be available
— Average multiplicity, — Average spectrum, — Average energy-angle spectrum,
• Generally, high-dimensional distributions of secondary particles are unavailable — Multiplicity distribution, — Multiplicity-dependent emission spectra, — Multiplicity-dependent energy-angle emission spectra, — Neutron-neutron, neutron-photon and photon-photon correlations — Too much data to tabulate!
n Default MCNP uses average quantities • Consider this a nuclear data “variance reduction” technique • Good for integral quantities, like flux and effective multiplication • Bad for studying detailed particle emission physics
Slide 4
χ (E)ν
χ (ν,E)χ (ν,E,θ )
P(ν )
χ (E,θ )
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2014 ANS Winter Meeting, Anaheim, CA
Secondary Particle Event Generators
MCNP6.1.1 contains two event generators:
n LLNL Fission Library1
• Spontaneous, neutron-induced and photo-fission • Fission Reaction Event Yield Algorithm (FREYA)2 isotopes:
— Spontaneous: 238U, 240Pu, 244Cm and 252Cf — Neutron-induced: 233U, 235U and 239Pu
• When available, FREYA generates secondary neutrons and photons
n Cascading Gamma-ray Multiplicity (CGM)3 - LANL
• Generates secondary particles from a variety of reactions • No fission! (CGMF under active development)
1J.M. Verbeke, C. Hagmann, and D. Wright, Lawrence Livermore National Laboratory, UCRL-AR-228518 (2014). 2R. Vogt and J. Randrup, Phys. Rev. C, vol. 84, pp. 044612-1-14 (2011). 3T. Kawano, P. Talou, M.B. Chadwick, and T. Watanabe, J. Nucl. Sci. Tech., 47 (5), 462-69 (2010).
Slide 5
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2014 ANS Winter Meeting, Anaheim, CA
Secondary Particle Event Generators: CGMF
n CGMF is a superset of CGM with an added fission reaction capability
n Fission fragments are sampled from a joint probability distribution function of mass (A), charge (Z) and total kinetic energy (TKE)
n Uses Hauser-Feshbach statistical theory of nuclear reactions
n Neutron / photon competition is treated during evaporation from fission fragments
n Monte Carlo is used to sample each step in the de-excitation process
Slide 6
4B. Becker, P. Talou, T. Kawano, Y. Danon, and I. Stetcu, Phys. Rev. C, 87, 014617 (2013).
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2014 ANS Winter Meeting, Anaheim, CA
Secondary Particle Event Generators: FREYA
n FREYA is LLNL’s fission event generator
n In MCNP6, it is accessible through LLNL Fission Package
n The LLNL Fission Package includes more tabulated and fitted data used for lesser known isotopes FREYA can’t presently handle
n FREYA uses a Monte Carlo Weisskopf approach • Neutrons emitted by sampling from Weisskopf spectrum • After neutrons are done emitting, gamma rays are emitted from residual energy
n Computationally more efficient than Monte Carlo Hauser-Feshbach
Slide 7
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2014 ANS Winter Meeting, Anaheim, CA
Numerical Results
n Implementation of CGMF into MCNP6 is underway
n Standalone and integrated code comparison needed for verification
n CGMF behavior is studied to understand trends and correlations
n Validation experiments will be needed to provide feedback to models
n For the following numerical results: • CGMF results are based on standalone code • FREYA used through LLNL Fission Package in MCNP6 • Default MCNP6 behavior is shown
n Average energy, multiplicity and gamma ray spectrum
n Secondary gamma ray spectrum
Slide 8
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2014 ANS Winter Meeting, Anaheim, CA
Numerical Results: Average Quantities
n Thermal neutron incident on 239Pu
n For MCNP6 and FREYA: • Secondary neutrons from
reaction • Secondary gamma rays
from , , etc.
n For CGMF (standalone): • Secondary neutrons and gamma rays
from only
n Discrepancies due to : • Multiplicity lower • Average energy higher • Peak at 5.5 MeV causes bump
n Check again after integration
Slide 9
Quantity MCNP6 FREYA CGMF
⌫̄N 2.8725 2.8723 2.9764⌫̄� 2.0 7.2973 9.1797
hEN i (MeV) 2.1034 2.0003 2.0327hE�i (MeV) 0.9949 1.0327 0.7728
10-6
10-5
10-4
10-3
10-2
10-1
100
0.1 1 10
Gam
ma-
ray S
pec
trum
(1/M
eV)
Outgoing Energy (MeV)
MCNP6FREYACGMF
(n,γ )(n, f )
(n, f )
(n, f )
(n,γ )
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2014 ANS Winter Meeting, Anaheim, CA
Numerical Results: Neutron and Gamma-ray Correlations
n Neutron – gamma ray energy and multiplicity correlations
n Analyzing CGMF results for n(th)+239Pu fission reaction
n Use to verify implementation into MCNP
n This physics needs to be validated with experiment
Slide 10
0
2
4
6
8
10
12
14
0 5 10 15 202.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
Ener
gy (
MeV
)
Neu
tron M
ult
ipli
city
Gamma-ray Multiplicity
Average Energy / Neutron
Total Neutron Energy / Fission
Average Energy / Gamma ray
Total Gamma-ray Energy / Fission
0
2
4
6
8
10
12
14
16
18
0 1 2 3 4 5 6 7 84.0
6.0
8.0
10.0
12.0
Ener
gy (
MeV
)
Gam
ma-
ray M
ult
ipli
city
Neutron Multiplicity
Average Energy / Neutron
Total Neutron Energy / Fission
Average Energy / Gamma ray
Total Gamma-ray Energy / Fission
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2014 ANS Winter Meeting, Anaheim, CA
Conclusions
n Many applications are in need of high fidelity physics models
n Fission event generators are under active development
n When implemented in MCNP a predictive capability may be possible
n SNM signature detection with code validation will soon be possible
n Future work: • Finish implementation and improvements to fission event generators in MCNP • Develop verification tests for all these new features • Need experimental measurements to compare against • Validate the new physics features with experiment • Compare against MCNP-PoliMi and other specialized codes
Slide 11
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2014 ANS Winter Meeting, Anaheim, CA
Questions?
This work was supported by the Office of Defense Nuclear Nonproliferation Research & Development (DNN R&D), National Nuclear Security
Administration, US Department of Energy.
Slide 12