Cross-section biasing

This example illustrates how to bias process cross-sections.

Generally speaking, the scheme consists of a G4VBiasingOperator that takes decisions on what sort of biasing is to be applied. The operator makes these decision on requests of the G4BiasingProcessInterface process. This process wraps an actual physics process and asks to the operator about what sort of biasing it should apply. This operator selects G4VBiasingOperation objects that implement the actual biasing content.

In the present case, the G4VBiasingOperation objects are

G4BOptnChangeCrossSection instances. This class is defined in processes/biasing/generic.

A first operator is defined to handle the case of one particle:

GB01BOptrChangeCrossSection .

The change of cross-section is generally speaking a change of process occurence. G4BOptnChangeCrossSection objets are then selected in the method:

G4VBiasingOperation* GB01BOptrChangeCrossSection::ProposeOccurenceBiasingOperation(...)

To allow this same cross-section change to be applied to several particle types, an other operator is defined

GB01BOptrMultiParticleChangeCrossSection which holds one GB01BOptrChangeCrossSection per particle type, and which delegates then everything to it.

The geometry is simple : a single volume to which an instance of GB01BOptrMultiParticleChangeCrossSection is attached to.

The wrapping of physics processes by G4BiasingProcessInterface processes is simply handled by the G4GenericBiasingPhysics physics constructor, as shown in the main program (see exampleGB01.cc).

Then, at whatever level (stepping action, or sensitive detector) the statistical weight of the track can be obtained as:

w = track->GetWeight() ;