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1 Example GB02 : force collision biasing
2 --------------------------------------
3
4 This example illustrates how to make a force collision biasing in a way
5 that is essentially the same than the MCNP one.
6
7 Generally speaking, the scheme consists of a G4VBiasingOperator that takes
8 decisions on what sort of biasing is to be applied. The operator makes these
9 decision on requests of the G4BiasingProcessInterface process. This process
10 wraps an actual physics process and asks to the operator about what sort of
11 biasing it should apply. This operator selects G4VBiasingOperation objects that
12 implement the actual biasing content.
13
14 In the present case, we make use of the biasing operator
15
16 G4BOptrForceCollision
17
18 that implements an "a la MCNP" force collision scheme for one particle type.
19 This operator is defined in processes/biasing/generic. It is a non-trivial
20 operator.
21 It starts by "splitting" the track at the volume entrance. Then this
22 track is forced to fly through the volume with no interaction. The
23 G4OptnForceFreeFlight biasing operation is used for that.
24 The second copy is then forced to interact within the volume, which is
25 handled by the G4BOptnForceCommonTruncatedExp operation : it is common as it
26 takes care of several processes by itself, and it applies a truncated
27 exponential law : ie and exponential law limited to the [0,L] range, L being
28 the volume width along the track flight.
29
30 To allow several particle types to undergo this force interaction scheme,
31 an other operator is defined
32
33 GB02BOptrMultiParticleForceCollision
34
35 which holds one G4BOptrForceCollision per particle type, and which
36 delegates then everything to it.
37
38 The geometry is simple : a single volume to which an instance of
39 GB02BOptrMultiParticleForceCollision is attached to.
40
41 The wrapping of physics processes by G4BiasingProcessInterface processes
42 is simply handled by the G4GenericBiasingPhysics physics constructor, as shown
43 in the main program.
44
45
46 Then, at whatever level (stepping action, or sensitive detector) the
47 statistical weight of the track can be obtained as:
48
49 w = track->GetWeight() ;
