1. Decay Process Makoto Asai (SLAC)
On behalf of Hisaya Kurashige (Kobe Univ.)
Geant4 Users SLAC
Feb. 19th, 2002

2. Decay process G4Decay Class is a process which manages
Decay at Rest
AtRestDoIt
mean life time = 
Decay in Flight　
PostStepDoIt
mean free path = c
Decay mode is given by Decay Table Information
G4DecayTable is a list of G4VDecayChannel.
G4VDecayChannel describes each decay mode.
Branching Ratio
Daughter Particle List
Decay Kinematics given by DecayIt method

3. Decay Channel G4VDecayChannel is an abstract class
Its derived classes are
G4PhaseSpaceDecayChannel :phase space
G4DalitzDecayChannel :p0 dalitz
G4MuonDecayChannel : m -> e n n decay
G4KL3DecayChannel :Kon semileptonic
G4NeutronBetaDecayChannel :neutron beta decay
See ‘Physics ReferenceManual’ for details of these decay modes
Users can easily define his new decay mode

4. Class Diagram

5. G4Decay::GPIL

6. G4Decay::DoIt

7. PreAssignedDecay User can assign Decay time Decay modes
to each primary track in its rest frame by using
PreAssignedDecayProperTime
PreAssignedDecayProducts
in G4DynamicParticle
Example: Decay by Event Generator
If daughter particles are written in HEPEVT format,
the parent keeps these information in PreAssignedDecayProducts
Decay time can be set by using G4PrimaryParticle::SetProperTime()

8. Radioactive decay
Long-term (>1s) radioactive decay induced by spallation interactions can represent an important contributor to background levels in space-borne -ray and X-ray instruments, as the ionisation events that result often occur outside the time-scales of any veto pulse.
The Radioactive Decay Model (RDM) treats the nuclear de-excitation following prompt photo-evaporation by simulating the production of , -, +,  and anti-, as well as the de-excitation -rays.
The model can follow all the descendants of the decay chain, applying, if required, variance reduction schemes to bias the decays to occur at user-specified times of observation.

9. RDM-specific user inputs
Radioactive decay
ENSDF2
Ion from G4 tracking
defined by A, Z, Q, nuclear
and atomic excitation state
Sample decay profile to
determine time of decay. If
stable do not process
User input defines
times of observation
for biasing decay
curve, splitting
of nuclei, and nuclide
decays to ignore
Radioactive
decay
Sample branching ratios
Geant4 Tracking
& process control
User input defines
Biasing of branching ratios
Sample secondaries and commit to stack. Determine nuclear recoil.
Photon-
evaporation
a, b, n
RDM-specific user inputs
Geant4 data sources
Apply photonuclear de-
excitation process g
Geant4 simulation