Download Geant4 User's Guide for Application Developers

Tracking and Physics
5.7. User Limits
5.7.1. General Concepts
The user can define artificial limits affecting to the Geant4 tracking.
G4UserLimits(G4double
G4double
G4double
G4double
G4double
uStepMax
uTrakMax
uTimeMax
uEkinMin
uRangMin
=
=
=
=
=
DBL_MAX,
DBL_MAX,
DBL_MAX,
0.,
0. );
uStepMax
Maximum step length
uTrakMax
Maximum total track length
uTimeMax
Maximum global time for a track
uEkinMin
Minimum remaining kinetic energy for a track
uRangMin
Minimum remaining range for a track
Note that uStepMax is affecting to each step, while all other limits are affecting to a track.
The user can assign G4UserLimits to logical volume and/or to a region. User limits assigned to logical volume
do not propagate to daughter volumes, while User limits assigned to region propagate to daughter volumes unless
daughters belong to another region. If both logical volume and associated region have user limits, those of logical
volume win.
A G4UserLimits object must be instantiated for the duration of whatever logical volume or region to which it
is assigned. It is the responsibility of the user's code to delete the object after the assigned volume(s)/region(s)
have been deleted.
5.7.2. Processes co-working with G4UserLimits
In addition to instantiating G4UserLimits and setting it to logical volume or region, the user has to assign the
following process(es) to particle types he/she wants to affect. If none of these processes is assigned, that kind of
particle is not affected by G4UserLimits.
Limitation to step (uStepMax)
G4StepLimiter process must be defined to affected particle types. This process limits a step, but it does
not kill a track.
Limitations to track (uTrakMax, uTimeMax, uEkinMin, uRangMin)
G4UserSpecialCuts process must be defined to affected particle types. This process limits a step and
kills the track when the track comes to one of these limits. Step limitation occurs only for the final step.
Example of G4UserLimits can be found in examples/basic/B2 : see B2aDetectorConstruction (or
B2bDetectorConstruction). The G4StepLimiter process is added in the Geant4 physics list via the
G4StepLimiterBuilder class in the main() function in exampleB4a.cc (or exampleB4b.cc ).
5.8. Track Error Propagation
The error propagation package serves to propagate one particle together with its error from a given trajectory state
until a user-defined target is reached (a surface, a volume, a given track length,...).
5.8.1. Physics
The error propagator package computes the average trajectory that a particle would follow. This means that the
physics list must have the following characteristics:
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