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Total Ionizing Dose Environment for a Jovian Mission Using Geant4

Total Ionizing Dose Environment for a Jovian Mission Using Geant4. Shawn Kang (a) , Michael Cherng (a) , Tom Jordan (b) , Insoo Jun (a) (a) JPL (b) EMPC. Introduction.

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Total Ionizing Dose Environment for a Jovian Mission Using Geant4

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  1. Total Ionizing Dose Environment for a Jovian Mission Using Geant4 Shawn Kang (a),Michael Cherng (a),Tom Jordan (b),Insoo Jun (a) (a) JPL (b) EMPC

  2. Introduction • At Jupiter, the most dominant particle constituent is the high-energy electrons with E > 1 MeV (and can be as high as >100 MeV). Huge mass is required to shield these electrons to reduce the radiation doses to the acceptable level for spacecraft electronics. • The dose-depth curve provides a convenient tool to estimate shielding mass or to assess the severity of space radiation environment. • G4GeneralParticleSource(GPS) and G4PEnergyDeposit classes to generate dose-depth curve. • G4GeneralParticleSource is suitable especially to space applications. • G4PEnergyDeposit is suitable because we want the accumulation of energy deposit for a run and have only one scorer. • Geant4 calculations were compared with other radiation transport codes commonly used in the space radiation applications: MCNPX and Novice. • Proper validation requires space measurements. Cherng, M.,I. Jun, T.,Jordan, “Optimum Shielding in Jovian Radiation Environment,” ISRP Paper, 2006.

  3. Dose-Depth Curve • At the start of a project we do not have a mechanical design, which means that we do not know what radiation shielding will be provided by the spacecraft. • So we calculate a dose/depth curve….. • A dose/depth curve gives you the dose at the center of your spacecraft, if your spacecraft is a spherical shell of aluminum. • If you are flying something more complicated than that, then there are still ways to get useful information out of the dose/depth curve.

  4. Europa Electron Energy Spectrum (GIRE, at 9.5Rj) (AE8, 160o west)

  5. Gean4 Input Setup PhysicsList Constructor { ----snipped --- G4VProcess* theeminusMultipleScattering = new G4MultipleScattering(); G4VProcess* theeminusIonisation = new G4eIonisation(); G4VProcess* theeminusBremsstrahlung = new G4eBremsstrahlung(); --- snipped ---} Scorer { --- snipped -- G4PSEnergyDeposit* scorer0 = new G4PSEnergyDeposit(psName="totalEDep"); // Attach the scorer to multi-functial-detector MFDet->RegisterPrimitive(scorer0); --- snipped} GPS /gps/particle e- /gps/pos/type Surface /gps/pos/shape Sphere /gps/pos/centre 0. 0. 0. cm /gps/pos/radius 6.56 cm /gps/ang/type cos /gps/ene/type User /gps/hist/type energy # # Europa 30 days # /gps/hist/point 0.1 0.0 # /gps/hist/point 0.2 2.60e-1 # /gps/hist/point 0.3 1.38e-1 # /gps/hist/point 0.5 1.57e-1 # /gps/hist/point 1.0 1.80e-1

  6. MCNPX 2.5 Input Setup phys:e 1000.0 phys:p 1000.0 c --- source definition --- c 30 days at Europa (GIRE Model with VIP4 Magnetic Field) electron spectrum c sdef sur=3 erg=d1 par=3 nrm=-1 si1 h 0.1 0.2 0.3 0.5 1.0 2.0 3.0 5.0 10.0 20.0 30.0 50.0 100.0 200.0 300.0 500.0 1000.0 c sp1 0.0 2.60E-01 1.38E-01 1.57E-01 1.80E-01 1.30E-01 5.17E-02 4.20E-02 2.78E-02 9.69E-03 2.13E-03 1.14E-03 4.90E-04 1.16E-04 1.98E-05 9.44E-06 3.61E-06 c c tally cards c *f8:e,p 1

  7. Novice Input Setup 'E Proton' proton inp 1.0 scale/ ,/1.00E-01 2.67E+16 2.00E-01 4.40E+15 3.00E-01 1.54E+15 5.00E-01 4.10E+14 1.00E+00 6.94E+13 2.00E+00 1.24E+13 3.00E+00 4.76E+12 5.00E+00 1.56E+12 / *adjoint,b=4, h=8192/ ,1/ detector point #1

  8. Shielding Geometry • A simple geometry as shown in below was modeled in this study. • Shielding thickness: 1 g/cm2 to 30 g/cm2. • Shielding material: aluminum and tungsten. • A series of Geant4, MCNPX, and NOVICE runs were performed for pure aluminum, pure tungsten, and aluminum (outer layer, 50% areal mass) plus tungsten (inner layer, 50% areal mass) representing low-Z/high-Z combination.

  9. Geant4 Benchmarking Copied from Geant4 Tutorial Package February 2006. Copied from Geant4 Tutorial Package February 2006.

  10. Aluminum Shielding

  11. Tungsten Shielding

  12. Aluminum and Tungsten Shielding, Novice

  13. Aluminum and Tungsten Shielding, Geant4

  14. Future Work • Agreement between the computer codes are pretty good. • Identify the source of the discrepancy: spectrum biasing, physics • More dose points : electron dominating region and bremsstrahlung dominating regions. • Other computer code results: penelope, EGS3, shieldose II, PHITS • Construct realistic geometry with Geant4. • Run-time benchmarking • Perform or obtain test data on spherical shell geometry

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