Example GB07

Leading particle biasing

This example illustrates how to use the leading particle biasing option.

It uses the G4BOptnLeadingParticle biasing operation located in:

source/processes/biasing/generic ,

and defines the following biasing operation to handle it:

GB07OptrLeadingParticle.

As a reminder, the generic biasing scheme consists of a G4VBiasingOperator that takes decisions on what sort of biasing technique to be applied. The techniques are called biasing operations, represented by the G4VBiasingOperation class. The operator is attached to a logical volume in which the biasing must happen. Decisions are made on requests of the G4BiasingProcessInterface process that messages the operator when the track is travelling in the volume. To equip the phyics list with this process, the G4GenericBiasingPhysics physics constructor is used. In this example, several processes -to which the technique is applied- are wrapped by this process to control their final state production for applying the biasing technique.

Geometry

The geometry is simply :

• a volume in which the biasing occurs and to which an instance of GB07OptrLeadingParticle is attached,
• a thin volume placed after the above volume, that is used to tally the particles exiting biasing volume.
• a sensitive detector is attached to the thin volume to simply print the particles entering here. In particular the statistical weight is printed, this one is obtained by:

w = track->GetWeight() ;

Biasing configuration

The particle types and processes under the leading particle biasing are visible in the main program exampleGB07.cc, these are:

pi+ and pi-,            inelastic process,
proton and anti-proton, inelastic process,
neutron,                inelastic and capture processes,
anti-neutron,           inelastic process,
gamma,                  conversion and photonNuclear processes,
electron,               electronNuclear process,
positron,               annihilation and positronNuceal processes,
pi0,                    decay process.

For the inelastic and lepto/gamma-nuclear processes, leading particle is applied in a rather classical way:

• keep the leading particle,
• keep one particle of each species (particles and anti-particles are considered a one species, and all hadrons with Z>=2 are counted as one species too).

For e+, e-, gamma and pi0 processes (which means in practice main conversion, annihililation and pi0 decay processes), the leading particle is kept, and the companion track(s) is(are) randomly kept/killed under a Russian roulette, with a 2/3 killing probabilty. See GB07BOptrLeadingParticle::StartTracking( ... ) for this killing probability setting.

Running the program:

The program can be run in batch or interactive mode and has the following options:

• batch mode:

  ./exampleGB07 [-m macro ]  [-b biasing {'on' = default,'off'}]
  

  or

  ./exampleGB07 [macro.mac]
  

• interactive mode:

  ./exampleGB07 [-b biasing {'on' = default,'off'}]