[Gate-users] Re: Gate-users Digest, Vol 5, Issue 9

[Chen, Yu]

Hi, Jan and Gaters,

Thanks for putting me to think hard about this step issue.

First, I would correct what I call interaction range cut before should
really mean a user defined step size cut. Range cut is called as production
threshold cut for secondaries.

In principle, "Transport" process implemanted in Geant4 can deal with:
1) particles crossing boundary; 2) charged particles in a field; 
3) particle transportation in the same volume *IF* all other interaction lengths 
   calculated from other physical processes are longer than user defined max allowed 
   step size through G4UserLimits method. This actually is a forced step with only 
   location and no mementum change, labelled as "Transportation" process.

However, since the default max allowed step size is DBL_MAX and no field involved in GATE
application, we may safely consider the tranportation process is only associated with the
change of volume.

Hope it is clear this time.

Yu Chen, Ph.D.
University of Massachusetts Medical School
Division of Nuclear Medicine
55 Lake Avenue North
Worcester, MA 01655-0243
Phone:  (508) 856-6123
Fax:    (508) 856-4572



-----Original Message-----
From: gate-users-bounces at lists.healthgrid.org on behalf of D.J. van der Laan
Sent: Fri 10/13/2006 1:57 PM
To: gate-users at lists.healthgrid.org
Subject: Re: [Gate-users] Re: Gate-users Digest, Vol 5, Issue 9
 
I do not think I completely understand what you mean. As far as I know
Geant4 does not limit the step size. The latest release has added this,
I think, but only for the multiple scattering processes, so I think this
will show up as a multiple scattering and not transport. But perhaps we
are talking about two different things.

I have used this trick in Geant4 to calculate fluencies through a
surface, and I have not noticed any transportation processes except on
volume boundaries.

The Gate hits file only has the volume id's of the volume in which the
interaction occurs, I do not know if this is the post or pre step point.
   So it is not possible to use this to detect 'real' boundary
crossings. Of course, it is possible to check if the interaction
position is on the surface of the volume.

Regards,

Jan



Chen, Yu wrote:
> 
> 
> I do not think "Transportation" process is only for the purpose
> of transporting between different volumes for particles.
> 
> Actually, a hit is a step in Geant4. When a particle travels more than
> a interaction range cut (defined as cut threshold) and if there is not
> a interaction (processes as compton, photoelectric etc) happened for this
> particle, then this step (hit) will be labled as "Transportation" process.
> 
> More accurate way to look for particles crossing a boundary is to find that
> step associated with prepoint in pre-volume and postpoint in post-volume.
> 
> Does GATE hit class have those volume names written out?
> 
> Please correct me if I am wrong and misleading. 
> 
> Yu Chen, Ph.D.
> University of Massachusetts Medical School
> Division of Nuclear Medicine
> 55 Lake Avenue North
> Worcester, MA 01655-0243
> Phone:  (508) 856-6123
> Fax:    (508) 856-4572
> 
> 

-- 
D.J. van der Laan
Delft University of Technology
Mekelweg 15, room 2.00.020
2629 JB Delft
The Netherlands

E: d.j.vanderlaan at tnw.tudelft.nl
T: +31 15 2783776
F: +31 15 2789011

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