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 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 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 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 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 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 # /gps/hist/point e-1 # /gps/hist/point e-1 # /gps/hist/point e-1 # /gps/hist/point e-1

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 phys:p 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 c sp E E E E E E E E E E E E E E E E-06 c c tally cards c *f8:e,p 1

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 E E E E E E E E E E E E E E E+12 /

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

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

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

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

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