[gate-users] Re:Re: no e-/e+ tracking!

[Chen, Yu]

Hello,

I would follow this interesting topic about e-/e+ tracking.

Generally, there are two issues in Geant4 considered separately:

1) e-/e+ production from various physics processes;
2) tracking of produced particles including e-/e+.

G4ProductionCutsTable takes care of issue 1) with method
SetEnergyRange(LowLimit, HighLimit). Here both LowLimit and HighLimit
are in energy unit (eV etc.).

G4ProductionCuts deals with issue 2) with method 
SetProductionCut(CutValue, ParticleName). As I know, this method
is the only way to change tracking threshold from Geant4 Verson 6 and it only takes
effect on Gamma, e- and e+ though you can still put other particles without error or
warning. CutValue is a minimum interaction range allowed for at least one step in material.
Hence you will get different cut-off energy thresholds for the same particle in different 
materials with the same production cut value (in unit mm etc.).

Then to the questions BG has:

Is it possible to get rid of all secondary e-/e+? 

Yes, if you turn off all processes to produce them e.g., Photoelectric, Compton.
But this is obviously not our intention. Since they are already produced, you of course would see 
them as hits no matter what production cut value you apply to them. 
However, you will see different count rates if you change LowLimit in energy range for your specific 
process. 

How to completely turn off the tracking of e+ and e- in Gate (or Geant4)?  

Make e+ and e- production cut values very large as suggested by Assen. This allows e-/e+ to deposit
their all energies in the first step of tracking. To see if this works, you can set a series of range cuts
(e.g., 1mm, 100mm, 10m) and compare the running time per event and the size of hits files for the same events
(with the same random numbers in the same machine?). You will gain a feeling on how much time you could save.

I would like to see someone correcting me if I am wrong.
I would be very happy to learn if you or someone can report the test results on this important topic.


By the way, the delta ray is the fast knock-out shell electrons produced by energetic *charged* particles.

The methods SetXRayCut and SetDeltaRayCut seem not to be implemented in GATTE for e-:

void GateElectronPhysics::SetXRayCut(G4double val)
{
  ;
}
 
void GateElectronPhysics::SetDeltaRayCut(G4double val)
{
  ;
}
 
and for gamma only PE process being implemented.

void GateGammaPhysics::SetXRayCut(G4double val)
{
  if ( m_photoElectricSelector == lowenergy_process)
  dynamic_cast<G4LowEnergyPhotoElectric*>(m_photoElectric)->SetCutForLowEnSecPhotons(val);
}
 
void GateGammaPhysics::SetDeltaRayCut(G4double val)
{
  ;
}
 

Best regards,
Yu


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: Bastien Guérin [mailto:guerin at bwh.harvard.edu]
Sent: Sun 7/24/2005 11:55 AM
To: gate-users at lphe1pet1.epfl.ch
Subject: [gate-users] Re:Re: no e-/e+ tracking!
 
Dear Assen,

the majority of the e- I want to get rid of are ejected by photoelectric
effect in the BGO and then tracked in that material. It is then not a
problem of a too low generation threshold.
The command which should prevent the tracking on these electrons is:
/gate/physics/setDeltaRayCut 10. MeV
and I don't understand why I still see e- in my ASCII gateHits.run files.

Am I the only one to have this problem?

All the best,

BG

----

Bastien Guerin
PhD candidate, University of Paris
Visiting Fellow, Harvard University
work: 617-525-6629
urgent: 617-817-2762

> 
> You may get e- with range larger than 100 mm in air (it is a global
> generation threshold).
> Make it 100 m.  But  that will save you only a little bit of time.
> Assen
> 
> Bastien Gu?rin wrote:
> 
>> Hi,
>> 
>> does anyone knows how to completely turn off the tracking of e+ and e- in
>> Gate? Even with the following parameters I still record e+/e- interactions
>> in my ASCII gateHits.run outputs, whereas I don't need them and it's highly
>> CPU consuming.
>> 
>> #       P H Y S I C S
>> 
>> 
>> #       EM  P R O C E S S
>> /gate/physics/gamma/selectRayleigh inactive
>> /gate/physics/gamma/gammaConversion inactive
>> /gate/physics/gamma/selectPhotoelectric standard
>> /gate/physics/gamma/selectCompton lowenergy
>> 
>> #       I N A C T I V E    S E C O N D A R Y   E L E C T R O N S
>> /gate/physics/setElectronCut 100. mm (the material is BGO)
>> 
>> #       I N A C T I V E    X - R A Y S
>> /gate/physics/setXRayCut 1. MeV
>> /gate/physics/setDeltaRayCut 10. MeV
>> 
>> /gate/physics/verbose 2
>> 
>> Many thanks,
>> 
>> BG
>> 
>> ----
>> 
>> Bastien Guerin
>> PhD candidate, University of Paris
>> Visiting Fellow, Harvard University
>> work: 617-525-6629
>> urgent: 617-817-2762
>> 
>> _______________________________________________
>> gate-users mailing list
>> gate-users at lphe1pet1.epfl.ch
>> http://lphe1pet1.epfl.ch/mailman/listinfo/gate-users
>> 
>> 
>> 


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