Hello Aaron,
GEANT has many ways why it decides to stop tracking a particle. You've
hit upon 2.
Some others are:
1) The particle's energy (momentum) falls below a predetermined
threshold. This is set with the FFREAD card "CUT".
2) The particle interacts, decays, etc.
If you are tracking really low energy protons, then 1 might have stopped
it. 
Maurik
On Thu, 2001-10-18 at 16:15, Aaron Joseph Maschinot wrote:
> 
> Hello, all:
> 
> Does anyone know what the condition(s) is (are) for GEANT to stop keeping
> track of a particle?  For example, I know one condition seems to be
> whether or not the particle has been tracked for 1000 steps.  This
> variable can be changed inside of "blast_init.f".  Another condition seems
> to be if the particle's total path length is greater than 600cm (i.e. the
> length of the radius of the LAS- volume).  Is this one true?  Where is this condition (and any others) set at?  I know that
> tracking stops when the variable ISTOP is set equal to zero, but I can't
> find where (and why) this is done.
> 
> Thanks,
> 
> Aaron
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