Pete Truscott & Fan Lei QinetiQ Ltd, Farnborough, UK Petteri Nieminen

1. Implementation of Nuclear-Nuclear Physics in the Geant4 Radiation Transport Toolkit forInterplanetary Space Missions Pete Truscott & Fan Lei QinetiQ Ltd, Farnborough, UK Petteri Nieminen ESTEC, Noordwijk, The Netherlands Johannes Peter Wellisch CERN, Geneva, Switzerland

2. Outline • Background and requirements • Geant4 • Total cross-section models implemented • Abrasion and EM dissociation final-state models implemented • Summary

3. Background and Requirements Species and energy range of source particles for interplanetary env. • GCR: • Very wide range in species, with noticeable dips after He and Fe • Typical energy range of concern: 10’s MeV/nuc - 100’s GeV/nuc, although mean energy is several hundred MeV/nuc. • Solar particle events 10’s MeV/nuc to ~1 GeV/nuc: • Impulsive, short-term events associated with solar flares have greater fraction of heavy particles • CMEs (Coronal mass ejection) produce gradual events that are proton-rich and last longer

4. Contribution of GCR and SPE ions very important to radiobiological dose in the interplanetary environment Background and Requirements Data from W Schimmerling, J W Wilson, F Cucinota, and M-H Y Kim, 1998.

5. Background and Requirements • Spacecraft engineers for future manned missions will require access to radiation shielding models like Geant4 to optimise design of spacecraft structure / habitat and mission profile • Models have to be applicable to energy range / particle species of GCR & SPE • Applicable target materials: • Man-made / transported materials such as: metal alloys of Al, Ti, Fe, Mg, Be; plastics and composites; fuels/oxidizers; deliberate shielding materials (polyethene, water); crew consumables/life-support • Mars atmosphere • Martian or Lunar soil / regolith (O, Si, Al, Fe, Mg, Ca), including composites with man-transported materials to form solid radiation shields

6. Work on extending QGS to treat nuclear-nuclear Very detailed model  time consuming Regime Model Application Parameterised Hadron-nucleon or hadron-nuclear Parton-string (>5GeV) Cosmic ray nuclei and Cascade (10MeV-10GeV) secondaries Trapped protons and secondaries QMD models Pre-compound (2-100 MeV) Secondary neutrons, including Low-energy neutron atmospheric/planetary albedo neutrons (thermal - 20 MeV) Induced radioactive background Isotope production calculations Evaporation (A>16) Treatment for seondaries from cosmic Nuclear ray nuclei and trapped protons, esp. de-excitation £ Fermi break-up (A 16) important in calculation of single event At the time could only treat hadron-nuclear interactions (Light-ion Binary Cascade code released Dec 04) effects ( microdosimetry) ³ Fission (A 65) Multi-fragmentation Photo-evaporation (ENSDF) Induced and natural radioactive Radioactive decay (ENSDF) backgrounds Any new models should complement and not duplicate other hadronics development in the Geant4 Collaboration.

7. Geant4 Inelastic Cross-Sections • Total cross-section models based on parametric fits: • proton-nuclear & neutron-nuclear interactions • Tripathi et al’s general algorithm for nuclear-nuclear • Others introduced in December Alternative model of Tripathi implemented for more accurate treatment of nuclear-nuclear collisions of light projectiles and/or targets • Final state models to determine exact interaction process and secondary particle production • Binary Cascade • Classical Cascade • Pre-equilibrium Abrasion (macroscopic) model and electromagnetic dissociation model being validated Total cross-section models allow rapid determination of mean-free paths, but cannot determine momentum change and secondary particle production

8. New Classes to Treat Total Cross-Sections for Nuclear-Nuclear Interaction • Tripathi’s empirical formula for light nuclear-nuclear interactions (where A4 for either projectile and/or target) - G4TripathiLightCrossSection • Class G4GeneralSpaceNNCrossSection automatically selects (depending upon projectile-target system) from: • G4TripathiCrossSection Tripathi “Standard” (NASA TP-3621, 1997) • G4TripathiLightCrossSection Tripathi “Light” (NASA TP-1999-209726) • G4IonsShenCrossSection Shen (Nucl Phys, A491, 1989) • G4ProtonInelasticCrossSection & G4IonsProtonCrossSection Wellisch (Phys Rev C51, No3, 1996)

9. Comparison of implementation of Tripathi “light” model with MathCAD algorithm and experiment -Al -Ta p- p-Li

10. G4WilsonAbrasionModel • In principle the abrasion model from Wilson’s NUCFRG2 should provide advantages in speed over microscopic simulation performed by cascade models or JQMD • Interaction region determined from geometric arguments • Nuclear density assumed constant • Number of “participants” in the overlap region based on approximation for nucleon mean-free path and maximum chord-length in the overlap region • NASA model follows this with ablation process - excitation from excess surface-area and kinetic energy transferred to nucleons • Can use standard Geant4 de-excitation models (evaporation, Fermi break-up, multi-fragmentation, and photo-evaporation) • Wilson Ablation model also included: uses NUCFRG2 algorithm for selecting which light nuclear fragments emitted from excited pre-fragment, and G4 evaporation to determine kinematics and recoil • Abraded nucleons from projected and target nucleus treated, as well as de-excitation of projectile and target pre-fragments

13. Comparison of the percentage of times the predicted cross-section for fragment production is within a factor of E of the experimental value (for various projectile nuclei on carbon target). • Abrasion model is better at predicting nuclear fragment yield using ablation (75% of time within factor-of-two) • Binary Cascade does worst at predicting nuclear fragment

14. Comparison of the predicted secondary proton spectrum from abrasion and Binary Cascade models, and experiment for 800MeV/nuc 20Ne on 20Ne (protons exiting at ~30o(left) and ~40o (right) • Binary Cascade model performs better than Abrasion model when predicting secondary nucleon spectrum >200 MeV

15. Nuclear EM Dissociation • Liberation of nucleons or nuclear fragments as a result of electromagnetic field, rather than the strong nuclear force • Important for relativistic nuclear-nuclear interaction, e.g. for 3.7GeV/nucleon 28Si projectiles in Ag, ED accounts for ~25% of the nuclear interaction events • NASA model used in HZEFRG and NUCFRG2 predict ED events for 1st and 2nd moments of electric field and cross-sections for giant dipole / quadrupole resonances • The G4EMDissociation model is an implementation of the NUCFRG2 physics • Applied for dissociation of protons and neutrons from both the projectile and target

16. Comparison of predicted and experimental EM dissociation cross-sections

17. Summary • New nuclear-nuclear models implemented in Geant4 for : • Abrasion model to simulate macroscopic production of pre-fragments • Version of Wilson’s ablation model • EM dissociation model simulating production of protons/neutrons for highly relativistic collisions • Improved / easier-to-use total interaction cross-section classes • New models complement other nuclear-nuclear physics developments in Geant4 (G4BinaryLightIonReaction, JQMD, QGSM) • Abrasion model provide more accurate prediction of nuclear fragment production • Results for Geant4 EM dissociation model generally consistent - within 5-42% of experiment

18. Backup slides

19. Comparison of G4EMDissociationCrossSection and HZEFRG1 predictions for EMD cross-section of 56Fe incident on a variety of targets.