1. 1 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 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. 2 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 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. 3 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 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. 4 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Europa Electron Energy Spectrum (AE8, 160 o west) (GIRE, at 9.5Rj)

5. 5 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 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="total EDep"); // 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. 6 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 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. 7 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Novice Input Setup *adjoint,b=4, h=8192/,1/ detector point #1 'E Proton' proton inp 1.0 scale/,/ 1.00E-012.67E+16 2.00E-014.40E+15 3.00E-011.54E+15 5.00E-014.10E+14 1.00E+006.94E+13 2.00E+001.24E+13 3.00E+004.76E+12 5.00E+001.56E+12 /

8. 8 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Shielding Geometry A simple geometry as shown in below was modeled in this study. Shielding thickness: 1 g/cm 2 to 30 g/cm 2. 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. 9 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Geant4 Benchmarking Copied from Geant4 Tutorial Package February 2006.

10. 10 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Aluminum Shielding

11. 11 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Tungsten Shielding

12. 12 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Aluminum and Tungsten Shielding, Novice

13. 13 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 Aluminum and Tungsten Shielding, Geant4

14. 14 4 th Geant4 Space Users’ Workshop and 3 rd Spenvis Users’ Workshop11/06/06-11/10/06 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