Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, 20-24 Sep 1999 Radioactive Decay Process and Data P Truscott and F Lei Space Department

Spacecraft Environment & Protection GroupGEANT4 Workshop, Noordwijk, 20-24 Sep 1999

Radioactive Decay Process and Data

P Truscott and F LeiSpace Department

DERA, Farnborough UK


Objectives

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).

Simulation to be applicable to:– nuclei at rest or in motion

– nuclei specified explicitly as primary particles or the product of nuclear interactions


Functionality

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)

Need to control the scope of the simulation:– range of nuclei for which process is applicable

– volumes for which process is applicable


Functionality (concluded)

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

Default operation is analogue Monte Carlo


Logical Design

Request update toDecayTable

Generation of decay table

Ion defined by A, Z, Q,nuclear and atomicexcitation state

Variance reduction to beapplied (including times ofobservation if VR selected)

Specification of range ofradionuclides to be treated &source particle time profile.

Sample decay profile todetermine time of decay. Ifstable do not process

Sample branching ratios

Branchingratio data& half-lives

Sample secondaries (, ,

) and commit to stack.Determine nuclear recoil

Apply photonuclear de-excitation process

DecayTable foreach nuclide& half-life data

Particle stack

Apply atomic relaxationprocess

-ray, e-

X-ray, Auger-e-

residual ion

(, e,

Initialisation

Application

Discardstablenucleus

Split nuclei beforesampling and/orbias exponentialcurve

Bias branchingratios

Russian Rouletteions after process

Specification of physicalvolumes in which to treatradioactive decay


Class Design Process:

– G4RadioactiveDecay process derived from G4VRestDiscreteProcess

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

Control:– G4RadioactiveDecayMessenger derived from G4UImessenger to allow control

of process through UI


Data Format and Sources

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

Radioactivity data need to be consistent with PhotoEvaporation (cross-reference of excitation energy)

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);


Technical Note covering much of the theory behind application of variance reduction to radioactive decay

G4Ion and G4IonTable have been modified to permit adequate description of nuclear and atomic state (Hisaya Kurashige)

Analogue Monte Carlo decay mostly implemented, with all decay modes possible

G4RadioactiveDecayMessenger allows restriction of range of radionuclei

Radioactivity database for the moment contains just a few example nuclei (for the purposes of testing)

Current Status


Future Work 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)

G4PhotoEvaporation:– does not simulate internal conversion electron emission (planned enhancement in ~1

year)– Problems with “DoChain” for G4VDiscreteGammaDeexcitation?

Develop a consistent data-base(s) for radioactive decay and nuclear de-excitation

Implement variance reduction schemes


Documentation Status

User Requirements Document issued at v1.0 Software Specification Document issued at v0.c Technical Note issued at v0.b

(Ref DERA/CIS/CIS2/7/36/4/9 and WWW page: http://www.space.dera.gov.uk/space_env/geant_docs/geant_docs.html)

Documents

Spacecraft Environment & Protection Group GEANT4 Workshop, Noordwijk, 20-24 Sep 1999 Radioactive Decay Process and Data P Truscott and F Lei Space Department