Overview
• Goal
• Introduction
SiC detector background
• Methods
TRIM simulation
• Results and Interpretation
• Radiation Damage
• Future Work 2
Goal
• Develop SiC Schottky diode detectors for measurement of
actinide concentrations, from alpha activities:
In a LiCl-KCl molten salt pyroprocessing electrolyte.
Identify greatest thickness of salt acceptable in front of the diode
detector’s front face.
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Detector Photo
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Background
Advantages of SiC semiconductor devices:
• Fast charge collection time
• Small mass
• Small size
• High break down electric field
(2.2 MV/cm, an order of magnitude higher than that in Si or GaAs)
• High band gap
(3.25 eV)
• Good radiation resistance
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Pyrochemical Process Fuel Cycle
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Methods
• Computer Simulation
TRIM
• Step I
Alpha range in the salt
Alpha range in the SiC
• Step II
Deposited energy in the active region of SiC
Multi-layer LiCl-KCl/SiC
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Actinides in the molten salt
Energy
of the
Weight
• Major Contributors Element Isotope
Percent
isotope
(MeV)
U & Pu U-234 0.458 4776
• U-6.4 wt% U-235 61.99 4398
• Pu-0.6 wt% Uranium U-236 1.61 4494
U-238 35.74 4197
Pu-238 0.128 5499
Pu-239 98.57 5156
Plutonium Pu-240 1.295 5168
Pu-241 0.015 4897
Pu-242 0.0001 4901
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Alpha contributors
Fraction of
Activity
alpha particles
Element Isotope (A=λn)
emitted per emitted
(dps)
alpha particle
U-234 9.85E-03 2.98E-03
U-235 4.64E-04 1.40E-04
Uranium U-236 3.60E-04 1.09E-04
U-238 4.16E-05 1.26E-05
Pu-238 7.11E-01 2.15E-01
Pu-239 1.99E+00 6.01E-01
Plutonium Pu-240 9.54E-02 2.89E-02
Pu-241 5.02E-01 1.52E-01
Pu-242 1.28E-07 3.87E-08 10
Step 1: To find the range of alpha in
LiCl-KCl salt and SiC active volume
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Simulation Methods
• Source
Alpha particles
Considered to be plane
Emitted perpendicularly into the target
• Target
LiCl-KCl
• Density 1.6225 g/cm3
• Diameter 300 μm
SiC active volume
• Density 3.2 g/cm3
• Diameter 300 μm
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Range of Alpha in LiCl-KCl
Energy of Range of alpha in
Isotope
alpha (MeV) LiCl-KCl (μm)
U-234 4.78 33.36
U-235 4.40 29.66
U-236 4.49 30.58
U-238 4.2 27.77
Pu-238 5.5 40.98
Pu-239 5.16 37.28
Pu-240 5.17 37.41
Pu-241 4.9 34.59
Pu-242 4.9 34.63
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Range of Alpha in SiC
Energy of Range of alpha in SiC
Isotope alpha (MeV) (μm)
U-234 4.78 14.92
U-235 4.40 13.25
U-236 4.49 13.66
U-238 4.2 12.40
Pu-238 5.5 18.35
Pu-239 5.16 16.68
Pu-240 5.17 16.74
Pu-241 4.9 15.47
Pu-242 4.9 15.49
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Step 2: Energy deposited in the active
volume
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Detector Configuration
LiCl-KCl 1 mm
SiC 20 mm
Diameter of LiCl-KCl & SiC: 300 μm
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Simulation Methods
• Multi-layer target
• Three Sub-Cases
Sub-Case 1
• Alpha particles perpendicularly incident on 1μm molten salt
layer (starts at 0 depth within the 1μm layer)
• Simulation was performed independently
• Considered 1000 alphas for each isotope
• Purpose:
To find the maximum energy deposited by individual isotope
Provide better understanding of the spectrum when all isotopes are blended
together
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Simulation Methods
Sub-Case 2
• Alpha particles distributed uniformly throughout the
volume of the salt
• Alpha particles of appropriate energy emitted
perpendicularly with respect to the detector face.
• Contribution to the spectrum weighted according to the
alpha activities
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Simulation Methods
Sub-Case 3
• Alpha particles distributed uniformly throughout the
volume of the salt
• Alpha particles of appropriate energy emitted
isotropically in direction space.
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Sub-Case 1:Results
Maximum energy
Isotope Alpha Energy (keV)
deposited in SiC (keV)
U-234 4776 4600
U-235 4398 4300
U-236 4494 4200
U-238 4197 4000
Pu-238 5499 5300
Pu-239 5156 5000
Pu-240 5168 5000
Pu-241 4897 4700
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Sub-Case 1:Results
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Sub-Case 2:Results
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Sub-Case 3:Results
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Step 2: Results
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Discussion
• The peak in the spectrum is attributed to the Pu-239 isotope.
• The Sub-Case 3 is the most accurate representation of physical
reality, this alpha particle energy deposition spectrum is most
important.
• The density of the LiCl-KCl molten salt that was considered for the
simulation corresponds to the pure salt. In reality, the salt is not
pure. The spectrum’s peak changes with change in density.
Therefore, this detector can account for the change in density of the
LiCl-KCl molten salt.
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Radiation Damage
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Multiscale Modeling of
Radiation Effects in SiC Detectors
n
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MCNP5
PKA Spectra TRIM /
MARLOWE
n-PKA
interactions PKA-target
Displacement interactions
damage
Molecular Kinetic
ab initio
Dynamics Monte Carlo
Very short-time Hopping rates and defect
formation energies
defect Defect
recombination
density
Electron Transport Effect of defects Compare with
Modeling electr. properties experiment
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Dose & Dose Rate Effects
50 kW
40
455 kW
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Future Work
• To perform experiments for measuring the actinide
concentration using the charge sensitive system.
• The simulation considered only U & Pu isotopes. In reality,
there may be contributions from Am-241 and Np-237,
whose effects are not known. Efforts are being made to
identify how these isotopes contribute to the spectrum.
• Study by calculations and experiments the effects of
temperature, dose and dose rate on the evolution of
detector’s electrical properties and pulse height resolution.
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Acknowledgements
• INL,DOE,NASA
• Our project group members
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