Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Radioactive Decay Process and Data P Truscott and F Lei Space Department DERA, Farnborough UK

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Objectives n Allow simulation by GEANT4 of: –Nuclear radioactive decay, i.e. ,  -,  +, electron capture (EC), and isomeric transition (IT) or “long-lived” meta-stable states, the latter through the existing photo-evaporation code; –Neutron decay (  - emission). n Simulation to be applicable to: –nuclei at rest or in motion –nuclei specified explicitly as primary particles or the product of nuclear interactions

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Functionality n All nuclear/neutron decay products to be submitted back to the tracking process, including –daughter nucleus (tracking interactions and radioactive decay through multiple generations) –  -rays from prompt de-excitation – & anti- –details of the atomic excitation state (EM atomic relaxation model) n Need to control the scope of the simulation: –range of nuclei for which process is applicable –volumes for which process is applicable

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Functionality (concluded) n Application of variance reduction techniques –bias decays to occur within user-defined times of observations –split radionuclei to increase sampling –apply minimum bias limit to ensure adequate sampling of low-probability channels which have high impact –apply a source particle flux-versus-time profile n Default operation is analogue Monte Carlo

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Logical Design

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Class Design n Process: –G4RadioactiveDecay process derived from G4VRestDiscreteProcess n Decay channel data: –G4NuclearDecayChannel derived from G4GeneralPhaseSpaceDecay –G4AlphaDecayChannel, G4BetaMinusDecayChannel, G4BetaPlusDecayChannel, G4KshellECDecayChannel, G4LshellECDecayChannel, G4ITDecayChannel derived from G4NuclearDecayChannel –The decay channel data are loaded whenever a “DecayIt” is requested for a new radionuclear species n Control: –G4RadioactiveDecayMessenger derived from G4UImessenger to allow control of process through UI

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Data Format and Sources n Radioactivity data to be distributed in ASCII text files: –Filename format consistent with PhotoEvaporation –Tabulated as a function of parent nucleus excitation energy and mean-lifetime –Data include decay mode, daughter nucleus excitation level, branching ratio, emitted particle end-point energy n Radioactivity data need to be consistent with PhotoEvaporation (cross-reference of excitation energy) n Possible methods of generating decay data –Derive decay and nuclear level data at the same time from ENSDF to ensure consistency - preferred option, but significant human intervention required due to irregular format (discussions with A Brunengo and H-P Wellisch continuing); –Derive only decay data from current ENSDF, and check consistency with current nuclear level data used by G4PhotoEvaporation; –Use decay data from DERA/UoS (derived from previous ENSDF);

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 n Technical Note covering much of the theory behind application of variance reduction to radioactive decay n G4Ion and G4IonTable have been modified to permit adequate description of nuclear and atomic state (Hisaya Kurashige) n Analogue Monte Carlo decay mostly implemented, with all decay modes possible n G4RadioactiveDecayMessenger allows restriction of range of radionuclei n Radioactivity database for the moment contains just a few example nuclei (for the purposes of testing) Current Status

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Future Work n Complete G4RadioactiveDecay process for analogue Monte Carlo only: –Coulomb correction for  ± –Modification of G4DynamicParticle properties to account for changes to atomic state following EC-decay –Distinction between “long-lived” and “short-lived” nuclear species (G4RadioactiveDecay including IT, or IT only, i.e. photo-evaporation) n G4PhotoEvaporation: –does not simulate internal conversion electron emission (planned enhancement in ~1 year) –Problems with “DoChain” for G4VDiscreteGammaDeexcitation? n Develop a consistent data-base(s) for radioactive decay and nuclear de-excitation n Implement variance reduction schemes

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, Sep 1999 Documentation Status n User Requirements Document issued at v1.0 n Software Specification Document issued at v0.c n Technical Note issued at v0.b (Ref DERA/CIS/CIS2/7/36/4/9 and WWW page: )