monte carlo methods in ads experiments
DESCRIPTION
Monte Carlo methods in ADS experiments. Study for state exam 2008 Mitja Majerle. “Phasotron” and “Energy Plus Transmutation” setups (schematic drawings). What are Accelerator Driven Systems ?. Accelerator Driven Systems. Subcritical reactor - PowerPoint PPT PresentationTRANSCRIPT
Monte Carlo methods in Monte Carlo methods in ADS experimentsADS experiments
Study for state exam 2008Study for state exam 2008
Mitja MajerleMitja Majerle
“Phasotron”
and
“Energy Plus Transmutation”
setups
(schematic drawings)
What are Accelerator Driven What are Accelerator Driven Systems ?Systems ?
Accelerator Driven SystemsAccelerator Driven Systems
Subcritical reactorSubcritical reactor Wider choice for reactor fuel (Wider choice for reactor fuel (238238U, U, 232232Th)Th) Transmutation of nuclear wasteTransmutation of nuclear waste Increased safetyIncreased safety
AcceleratorAccelerator Protons or light ions of energy around 1 GeVProtons or light ions of energy around 1 GeV Very high powers (hundreds of MW)Very high powers (hundreds of MW) Stable beamStable beam
Spallation reactionSpallation reaction
SpallationSpallation(process in which hadrons or light ions are ejected (process in which hadrons or light ions are ejected
from the nucleus due to impact of relativistic particle)from the nucleus due to impact of relativistic particle)
In textbooks divided In textbooks divided to two phases:to two phases: Intra Nuclear CascadeIntra Nuclear Cascade De-excitation De-excitation
(evaporation, fission)(evaporation, fission) INC phase has to be INC phase has to be
corrected at lower corrected at lower energies to fit the energies to fit the experiments – experiments – preequilibrium phasepreequilibrium phase
CalculationsCalculations
Monte Carlo method:Monte Carlo method: Event by event simulation on nuclear scale Event by event simulation on nuclear scale Accuracy Accuracy sqrt(N) sqrt(N) sqrt(calculation time), sqrt(calculation time), Parallelization is possible (MPI, PBS)Parallelization is possible (MPI, PBS)
Used codes: MCNPX, FLUKAUsed codes: MCNPX, FLUKA Resources:Resources:
CESNET Meta CentrumCESNET Meta Centrum 56 processors on OJS (MPI and PBS)56 processors on OJS (MPI and PBS)
How MC code worksHow MC code works Pseudorandom numbers - Pseudorandom numbers - Example - photon source in matter:Example - photon source in matter:
Determine track (Determine track (for direction)for direction) Determine where the reaction will happen - l=1/Determine where the reaction will happen - l=1/ ln( ln( Determine which interaction will happen (photoeffect, Determine which interaction will happen (photoeffect,
Compton, pair production …) - Compton, pair production …) - Determine angles – Determine angles – , energies of generated particles , energies of generated particles
(physics)(physics) Loop until particles escape from the phase space of interestLoop until particles escape from the phase space of interest
Tallying:Tallying: Count the particles that passed through selected phase Count the particles that passed through selected phase
space (surfaces, volumes, deposited energy …)space (surfaces, volumes, deposited energy …) Precision and accuracy:Precision and accuracy:
Wrong physics => wrong results Wrong physics => wrong results Central limit theorem – for large N, Central limit theorem – for large N,
results distribution approach results distribution approach normal distributionnormal distribution
Phasotron experimentPhasotron experiment Simple, lead target (diameter 10 cm, Simple, lead target (diameter 10 cm,
length 0.5 m)length 0.5 m) Intensive protons 660 MeV, 10 minIntensive protons 660 MeV, 10 min Activation detectors, iodine samples (Activation detectors, iodine samples (129129I)I)
Simulated neutron spectrumSimulated neutron spectrum
NAA experimental dataNAA experimental data
1E-8
1E-7
1E-6
1E-5
1E-4
0 10 20 30 40 50
Position along the target [cm]
B [g
-1 p
roto
n-1
] Au-198
Au-196
Au-194
Au-193
Au-192
Au-191
proton range
Exp/sim comparisonsExp/sim comparisons
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 10 20 30 40 50
Position along the target [cm]
Exp
erim
ent/
calc
ula
tio
n
Na-24Au-196Au-194Au-192Au-191
MCNPX - INCL4/ABLA
MCNPX – CEM03
FLUKA
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 10 20 30 40 50
Position along the target [cm]
Exp
erim
ent/
calc
ula
tio
n
Na-24Au-196Au-194Au-192Au-191
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0 10 20 30 40 50
Position along the target [cm]
Exp
erim
ent/
calc
ula
tio
n
Na-24Au-196Au-194Au-192Au-191
Proton influenceProton influence
Proton fluence in the target central plane – around 30th cm protons are scattered out of the target
Contribution of proton reactions to total reaction rate
0
1
2
3
4
5
6
0 10 20 30 40
Position along the target [cm]
Prod
uctio
n ra
te [1
0-7
g-1
pro
ton
-1]
sum(n,7n)(p,6np)
Iodine samplesIodine samples
0
0.5
1
1.5
2
I-130 I-128 I-126 I-124 I-123 I-121 I-120 I-119 I-118
Produced isotope
expe
rim
ent/s
imul
atio
n
I-127
I-129
0
0.5
1
1.5
2
I-130 I-128 I-126 I-124 I-123 I-121 I-120 I-119 I-118
Produced isotope
expe
rim
ent/s
imul
atio
n
I-127
I-129
Sample 1 – 9th cm Sample 2 – 21st cm
Systematic uncertaintiesSystematic uncertainties
Simulations with changed Simulations with changed parameters are comparedparameters are compared Beam parameters (3 mm ~ 15% Beam parameters (3 mm ~ 15%
uncertainty)uncertainty) Detector displacement (1 mm ~ <5%)Detector displacement (1 mm ~ <5%)
Worse situation:Worse situation: Around 30Around 30thth cm, protons exit the target, cm, protons exit the target,
beam parameters have bigger influencebeam parameters have bigger influence Iodine samples – not precise placementIodine samples – not precise placement
Energy Plus TransmutationEnergy Plus Transmutation
SABRINA plot from MCNPX input file, provided by J. Šolc.
MC analysisMC analysis
Influence of setup parts Influence of setup parts polyethylene boxpolyethylene box iron and detectors have negligible influenceiron and detectors have negligible influence
Systematic uncertainties – Systematic uncertainties – displacements:displacements: incident beam : 3mm = 15-20% uncertaintyincident beam : 3mm = 15-20% uncertainty detectors displacement: 5mm = 20%detectors displacement: 5mm = 20% The calculations apply only to threshold The calculations apply only to threshold
activation detectors.activation detectors.
PolPolyethylene box –yethylene box –biological shieldingbiological shielding
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
1E-2
1E-1
1E-9 1E-6 1E-3 1E+0 1E+3Energy [MeV]
Nn
eu
tro
ns [
cm
-2 p
roto
n-1]
target-blankettb+boxtb+box+Cd
10-9 10-6 10-3 1 103
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-1
1E-5
1E-4
1E-3
1E-2
1E-1
1E+0
1E+1
1E-9 1E-6 1E-3 1E+0 1E+3Energy [MeV]
Nn
eu
tro
ns [
pro
ton-1
]
without shielding
with shielding
10-9 10-6 10-3 1 103
10-1
10-2
10-3
10-4
10-5
1
10
Neutron spectra inside box
Neutron spectra emitted to environment
0.8
0.9
1.0
1.1
1.2
1.3
0.1 1 10 100 1000
Energy [MeV]
Rat
io
tg+box/tgtg+box+Cd/tg
10-1 1 10 102 103
Neutron production, kNeutron production, keffeff
At 1.5 GeV At 1.5 GeV experiment, 50 experiment, 50 neutrons were neutrons were produced per protonproduced per proton
Maximum production Maximum production (proton(proton-1-1 GeV GeV-1-1) in 1-) in 1-1.5 GeV range1.5 GeV range
kkeffeff=0.202=0.202 flooded with water kflooded with water keffeff
rises to 0.41 (and rises to 0.41 (and heavy water 0.26)heavy water 0.26)
Total neutron production with the EPT setup.
0
5
10
15
20
25
30
35
0 1 2 3
Beam energy [GeV]
Nn
eutr
on
s[p
roto
n-1
GeV
-1]
MC vs. experimentMC vs. experiment
Good agreement Good agreement below 1.25 AGeVbelow 1.25 AGeV
Wrong predictions Wrong predictions at 1.5 and 2 GeVat 1.5 and 2 GeV
Similar behavior Similar behavior reported for thin reported for thin target experiments target experiments – could there be – could there be any connection ?any connection ?
0
1
2
3
4
0 5 10 15
Radial distance [cm]
Bex
p/B
sim
Au-196Au-194Au-193Au-192Au-191
FLUKA calculations of reaction rates in Au detectors placed in the first gap
ConclusionConclusion Phasotron experimentPhasotron experiment
Completely analyzedCompletely analyzed Good agreement with MC codesGood agreement with MC codes Uncertainties ca. 15%Uncertainties ca. 15%
EPTEPT All performed experiments (4x protons, 2x deuterons) were All performed experiments (4x protons, 2x deuterons) were
simulatedsimulated Significant disagreement with MC codes at higher energiesSignificant disagreement with MC codes at higher energies Uncertainties 30%Uncertainties 30%
OutlooksOutlooks MC in spectrometry – revision of spectrometry methods MC in spectrometry – revision of spectrometry methods
used at our work (precision of different corrections: used at our work (precision of different corrections: geometrical, COI …)geometrical, COI …)
Is EPT disagreement connected with thin target experiments Is EPT disagreement connected with thin target experiments ??
Acknowledgments to META Centrum, where most of presented calculations were performed.