Implementation of Nuclear-Nuclear Physics in the Geant4 Radiation Transport Toolkit for Interplanetary 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 Background and Requirements Data from W Schimmerling, J W Wilson, F Cucinota, and M-H Y Kim, Contribution of GCR and SPE ions very important to radiobiological dose in the interplanetary environment

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

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 Total cross-section models allow rapid determination of mean-free paths, but cannot determine momentum change and secondary particle production Final state models to determine exact interaction process and secondary particle production Binary Cascade Classical Cascade Pre-equilibrium Alternative model of Tripathi implemented for more accurate treatment of nuclear-nuclear collisions of light projectiles and/or targets Abrasion (macroscopic) model and electromagnetic dissociation model being validated

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 ) –G4IonsShenCrossSection Shen (Nucl Phys, A491, 1989) –G4ProtonInelasticCrossSection & G4IonsProtonCrossSection Wellisch (Phys Rev C51, No3, 1996)

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

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

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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 20 Ne on 20 Ne (protons exiting at ~30 o (left) and ~40 o (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 28 Si projectiles in Ag, ED accounts for ~25% of the nuclear interaction events NASA model used in HZEFRG and NUCFRG2 predict ED events for 1 st and 2 nd 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 56 Fe incident on a variety of targets.