ns of Monte Carlo Code for a Gamma Resonance System Analysis ns of Monte Carlo Code for a Gamma Resonance System Analysis L. Wielopolski, A. Hanson, I. Dioszegi, M. Todosow, Brookhaven National Laboratory, Environmental Sciences Department, Upton, NY 11973 POC – Lucian Wielopolski, E-mail: [email protected] Objective To implement Monte Carlo calculations using MCNP code for the analysis and optimization of a Gamma Nuclear Resonance Absorption (GNRA) and Gamma Fission (GF) systems. These systems are planned for detection of explosives and nuclear materials concealed in either small packages or large shipping cargo containers. GNRA is based on element specific nuclear resonance absorption of high energy gamma radiation, whereas GF is based on a photofission reaction that occurs in fissionable material at above ~ 6MeV threshold energy. GF results in prompt and delayed neutrons that can be measured using neutron detectors. The usefulness of the proposed approaches has been demonstrated for GNRA using 9.17 MeV gamma radiation for detection of nitrogen present in the explosives and, for GF, using a 6 MeV Bremsstrahlung radiation for detection of delayed neutrons in fissionable material. The main hurdle to overcome in implementing MCNP for GNRA is the lack of photon cross sections libraries that include photon nuclear resonance interactions. Thus these cross sections need to be prepared on individual basis for each element of interest and then incorporated into the existing standard MCNP cross section libraries. One MCNP library has been modified for the 9.17 MeV level in the nitrogen, however, in its current configuration it does not include the angular correlation given by (1-0.44P 2 ). Although this is not critical for transmission calculations it will be important to consider for nuclear fluorescence calculations. Summary • It is critically important for gamma nuclear resonance absorption measurements to modify the cross section libraries for MCNP to include the nuclear resonance cross sections for the elements of interest. At present only the nitrogen library has been modified. • For nuclear fluorescence it is equally important to ascertain that cross sections have been modified for all nuclear levels of interest and that angular correlation of gamma emission is included. At present these two factors are not included in the cross sections. • Use of additional regular detectors to measure nuclear fluorescence simultaneously with the transmitted radiation will improve the signal. • Nuclear fluorescence spectra are preferably collected in a backward configuration reducing the Compton scattered to the detector and shifting its energy below 500 keV. • Controlling factor in a stand off configuration is the inverse square distance from the nuclear fluorescence to the detector. The attenuation in air is manageable even at large distances. The results will depend on positioning of the detectors. • Initial simulations of the transmission through an explosive A Gamma Resonance System A GNRA system consists of a proton accelerator equipped with a suitable target material upon which impinging protons produce a resonance gamma beam via a proton resonance (p,) reaction. The resonance gamma radiation attenuation by the nitrogen present in the explosive is measured in the transmission mode using nitrogen resonance detectors . The nitrogen signature is indicative of presence of explosive. Alternatively elements can also be measured in nuclear resonance fluorescence mode by placing regular detectors around the inspected container. Each element in the system as well as the configuration of the entire system require engineering-optimization that can be accomplished using MCNP calculations. Two aspects of nuclear fluorescence yield and gamma energy distribution together with stand off calculations are presented below. Nitrogen Cross Sections 8.80 8.92 9.04 9.16 9.28 9.40 Energy (M eV ) 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 A ttenuation (barns/atom ) Breit-W igner C rossSection at9.17 M eV in N itrogen 10 -3 10 -2 10 -1 10 0 10 1 10 2 Energy (M eV ) 10 -2 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 A ttenuation (barns/atom ) TotalA ttenuation, Photoelectric, C om pton, Pair Production,6 R esonance M assA ttenuation ofN itrogen and at9.17 M eV G am m a R esonance 0 30 60 90 120 150 180 Teta (degrees) 0.5 0.7 0.9 1.1 1.3 1.5 A ngular C orrelation N itrogen A ngular C orrelation for 9.17 M eV Level 1-0.44P 2 (cosq) The angular correlation is maximum at 90° that need to be considered when optimizing a stand off system based on nuclear fluorescence. Resonance cross section is given by the Breit-Wigner formula: abi = 2 g a b i (E-E R ) 2 + 2 /4 where g is a statistical factor given by: g = 2J + 1 (2s + 1)(2i + 1) Nuclear Absorption versus Nuclear Fluorescence 0 2 4 6 8 10 Energy (M eV ) 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 G am m a Y ield ( /Sr/ source ) IncidentG am m a on the D etector Surface atA lpha 0 0 2 4 6 8 10 Energy (M eV ) 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 G am m a Y ield ( /Sr/ source ) IncidentG am m a on the D etector Surface atA lpha 45 0 2 4 6 8 10 Energy (M eV ) 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 G am m a Y ield ( /Sr/ source ) IncidentG am m a on the D etector Surface atA lpha 90 0 2 4 6 8 10 Energy (M eV ) 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 G am m a Y ield ( /Sr/ source ) IncidentG am m a on the D etector Surface atA lpha 135 0 2 4 6 8 10 Energy (M eV ) 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 G am m a Y ield ( /Sr/ source ) IncidentG am m a on the D etector Surface atA lpha 180 A hypothetical spherical detector (in gray) surrounds an explosive with a mass m that is irradiated with a gamma beam emanating from a proton accelerator. The incident gamma beam is partially attenuated by the atomic interactions and partially by nuclear resonance interactions with nitrogen. The energy distributions of the gamma radiation incident on the detector surface at 0, 45, 90,135, and 180 degrees are shown in the spectra above. These results show that; 1) it is conceivable to measure gamma radiation resulting from the nuclear fluorescence and 2) the backward angles are preferable over forward angles due to reduced Compton background. 0 30 60 90 120 150 180 A ngle ( ) 1.0*10 -003 1.5*10 -003 2.0*10 -003 2.5*10 -003 G am m a Y ield (gam m as/Sr) M 15kg M 10kg M 5kg M 05kg M 025kg M 01kg M 005kg N uclear Fluorescence Y ield For V arious Explosive M assM Increased mass of the explosive increases the yield of nuclear fluorescence in the backward angles. This results from competition between penetration of the incident resonance radiation and escape of the fluorescence radiation that is out of resonance toward the detector. Stand – off Calculations Source emission : 270 /s/cm 2 /mA at distance of 1 m Cotton density: 0.3 g/cm 3 , (C 6 H 10 O 5 ) n , / = 0.0219 cm 2 /g HMX: 1.9 g/cm 3 , (C 4 H 8 N 8 O 8 ), / = 0.0216 cm 2 /g on resonance / = 0.0623 cm 2 /g Detector: BaF 2 , 4.89 g/cm 3 Air (weight fraction): 14 N 0.755, 16 O 0.232, Air Density: 0.001225 g/cm 3 Air Attenuation: off resonance / = 0.021 cm 2 /g, N Attenuation on resonance / = 0.052 cm 2 /g, (exp) 366 11% 23% 46% 300 244 23% 38% 60% 200 122 48% 62% 77% 100 61 69% 79% 88% 50 12 92% 95% 97% 10 Tota l On Resonance Off Resonance Pixel Size (cm) Transmission In Air Distanc e (m) 8.810 -11 2.010 -10 7.910 -10 3.210 -9 7.910 -8 Geomet. Factor 1/4r 2 Stand Off Considerations Transmission profile of HMX explosive (5cm radius, 4 cm thick ) embedded in an LD3 container filled up with cotton, detected by twenty one BaF 2 detectors. Initial System Modeling Photon energy distribution in- and out- of resonance impinging upon a single detector after traversing 50 m of air, using 10 eV wide scoring beans the additional attenuation due to resonance cross section is clearly visible. 1. 2. 3. 4. Cluster # BaF 2 Detectors Filled Container d Explosive r Point Source E=9.17225 MeV
Applications of Monte Carlo Code for a Gamma Resonance System Analysis L. Wielopolski, A. Hanson, I. Dioszegi, M. Todosow, Brookhaven National Laboratory,
Jan 17, 2016
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Applications of Monte Carlo Code for a Gamma Resonance System AnalysisApplications of Monte Carlo Code for a Gamma Resonance System AnalysisApplications of Monte Carlo Code for a Gamma Resonance System AnalysisApplications of Monte Carlo Code for a Gamma Resonance System Analysis
L. Wielopolski, A. Hanson, I. Dioszegi, M. Todosow,Brookhaven National Laboratory,Environmental Sciences Department, Upton, NY 11973POC – Lucian Wielopolski, E-mail: [email protected]
Objective
To implement Monte Carlo calculations using MCNP code for the analysis and optimization of a Gamma Nuclear Resonance Absorption (GNRA) and Gamma Fission (GF) systems. These systems are planned for detection of explosives and nuclear materials concealed in either small packages or large shipping cargo containers. GNRA is based on element specific nuclear resonance absorption of high energy gamma radiation, whereas GF is based on a photofission reaction that occurs in fissionable material at above ~ 6MeV threshold energy. GF results in prompt and delayed neutrons that can be measured using neutron detectors. The usefulness of the proposed approaches has been demonstrated for GNRA using 9.17 MeV gamma radiation for detection of nitrogen present in the explosives and, for GF, using a 6 MeV Bremsstrahlung radiation for detection of delayed neutrons in fissionable material.
The main hurdle to overcome in implementing MCNP for GNRA is the lack of photon cross sections libraries that include photon nuclear resonance interactions. Thus these cross sections need to be prepared on individual basis for each element of interest and then incorporated into the existing standard MCNP cross section libraries. One MCNP library has been modified for the 9.17 MeV level in the nitrogen, however, in its current configuration it does not include the angular correlation given by (1-0.44P2). Although this is not critical for transmission calculations it will be important to consider for nuclear fluorescence calculations.
Summary • It is critically important for gamma nuclear resonance absorption measurements to modify the
cross section libraries for MCNP to include the nuclear resonance cross sections for the elements of interest. At present only the nitrogen library has been modified.
• For nuclear fluorescence it is equally important to ascertain that cross sections have been modified for all nuclear levels of interest and that angular correlation of gamma emission is included. At present these two factors are not included in the cross sections.
• Use of additional regular detectors to measure nuclear fluorescence simultaneously with the transmitted radiation will improve the signal.
• Nuclear fluorescence spectra are preferably collected in a backward configuration reducing the Compton scattered to the detector and shifting its energy below 500 keV.
• Controlling factor in a stand off configuration is the inverse square distance from the nuclear fluorescence to the detector. The attenuation in air is manageable even at large distances.
The results will depend on positioning of the detectors.
• Initial simulations of the transmission through an explosive using a monoenergetic gamma beam and of transmission through air using energy distributed source demonstrate the extra resonance attenuation.
A Gamma Resonance System
A GNRA system consists of a proton accelerator equipped with a suitable target material upon which impinging protons produce a resonance gamma beam via a proton resonance (p,) reaction. The resonance gamma radiation attenuation by the nitrogen present in the explosive is measured in the transmission mode using nitrogen resonance detectors. The nitrogen signature is indicative of presence of explosive. Alternatively elements can also be measured in nuclear resonance fluorescence mode by placing regular detectors around the inspected container. Each element in the system as well as the configuration of the entire system require engineering-optimization that can be accomplished using MCNP calculations. Two aspects of nuclear fluorescence yield and gamma energy distribution together with stand off calculations are presented below.
abi = 2g
Nitrogen Cross Sections
8.80 8.92 9.04 9.16 9.28 9.40
Energy (MeV)
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
102
Att
enu
ati
on
(b
arn
s/ato
m)
Breit-Wigner Cross Sectionat 9.17 MeV in Nitrogen
10-3 10-2 10-1 100 101 102
Energy (MeV)
10-2
10-1
100
101
102
103
104
105
Att
enu
ati
on
(b
arn
s/ato
m)
Total Attenuation,
Photoelectric, Compton,
Pair Production, 6
Resonance
Mass Attenuation of Nitrogenand at 9.17 MeV Gamma Resonance
0 30 60 90 120 150 180
Teta (degrees)
0.5
0.7
0.9
1.1
1.3
1.5
An
gu
lar
Co
rrel
ati
on
Nitrogen Angular Correlation for 9.17 MeV Level 1-0.44P2(cosq)The angular correlation is
maximum at 90° that need to be considered when optimizing a stand off system based on nuclear fluorescence.
Resonance cross section is given by the Breit-Wigner formula:
abi = 2gabi
(E-ER)2 + 2/4where g is a statistical factor given by:
g = 2J + 1
(2s + 1)(2i + 1)
Nuclear Absorption versus Nuclear Fluorescence
0 2 4 6 8 10
Energy (MeV)
10-5
10-4
10-3
10-2
10-1
100
101
Gam
ma
Yie
ld (/
Sr/ s
ourc
e)
Incident Gamma on the Detector Surface at Alpha 0
0 2 4 6 8 10
Energy (MeV)
10-7
10-6
10-5
10-4
10-3
10-2
Gam
ma
Yie
ld (/
Sr/ s
ourc
e)
Incident Gamma on the Detector Surface at Alpha 45
0 2 4 6 8 10
Energy (MeV)
10-7
10-6
10-5
10-4
10-3
10-2
Gam
ma
Yie
ld (/
Sr/ s
ourc
e)
Incident Gamma on the Detector Surface at Alpha 90
0 2 4 6 8 10
Energy (MeV)
10-7
10-6
10-5
10-4
10-3
10-2
Gam
ma
Yie
ld (/
Sr/ s
ourc
e)
Incident Gamma on the Detector Surface at Alpha 135
0 2 4 6 8 10
Energy (MeV)
10-7
10-6
10-5
10-4
10-3
10-2
Gam
ma
Yie
ld (/
Sr/ s
ourc
e)
Incident Gamma on the Detector Surface at Alpha 180
A hypothetical spherical detector (in gray) surrounds an explosive with a mass m that is irradiated with a gamma beam emanating from a proton accelerator. The incident gamma beam is partially attenuated by the atomic interactions and partially by nuclear resonance interactions with nitrogen. The energy distributions of the gamma radiation incident on the detector surface at 0, 45, 90,135, and 180 degrees are shown in the spectra above. These results show that; 1) it is conceivable to measure gamma radiation resulting from the nuclear fluorescence and 2) the backward angles are preferable over forward angles due to reduced Compton background.
0 30 60 90 120 150 180
Angle ( )
1.0*10-003
1.5*10-003
2.0*10-003
2.5*10-003
Gam
ma
Yie
ld (
gam
mas
/Sr)
M15kgM10kgM5kgM05kgM025kgM01kgM005kg
Nuclear Fluorescence Yield For Various Explosive Mass MIncreased mass of the explosive
increases the yield of nuclear fluorescence in the backward angles. This results from competition between penetration of the incident resonance radiation and escape of the fluorescence radiation that is out of resonance toward the detector.
Stand – off Calculations
Source emission : 270 /s/cm2/mA at distance of 1 mCotton density: 0.3 g/cm3, (C6H10O5)n, / = 0.0219 cm2/gHMX: 1.9 g/cm3, (C4H8N8O8), / = 0.0216 cm2/g
on resonance / = 0.0623 cm2/gDetector: BaF2, 4.89 g/cm3
Air (weight fraction): 14N 0.755, 16O 0.232, Air Density: 0.001225 g/cm3
Air Attenuation: off resonance / = 0.021 cm2/g, N Attenuation on resonance / = 0.052 cm2/g, (exp)
36611%23%46%300
24423%38%60%200
12248%62%77%100
6169%79%88%50
1292%95%97%10
TotalOn
Resonance
Off
Resonance
Pixel
Size
(cm)
Transmission In AirDistance
(m)
8.810-11
2.010-10
7.910-10
3.210-9
7.910-8
Geomet.Factor
1/4r2
Stand Off Considerations
Transmission profile of HMX explosive (5cm radius, 4 cm thick ) embedded in an LD3 container filled up with cotton, detected by twenty one BaF2 detectors.
Initial System Modeling
Photon energy distribution in- and out- of resonance impinging upon a single detector after traversing 50 m of air, using 10 eV wide scoring beans the additional attenuation due to resonance cross section is clearly visible.
1.
2.
3.
4.
Cluster #
BaF2 Detectors
Filled Container
d
Explosive
r
Point SourceE=9.17225 MeV
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