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Question Magnetic Field from field01 Example 

Keywords: magnetic field ield01
Forum: Fields: Magnetic and Otherwise
Date: 13 Jul, 2007
From: Matthew Middione <>

It is probabbly apparent by my multiple magnetic field postings on the 
forum that I am having difficulties getting my magnetic field to work.

The basic run down of my situation is as follows.  I am using code from 
TestEm1 (Geant/examples/extended/electromagnetic/TestEm1) and exGPS 
(Geant/examples/extended/eventgenerator/exGPS).  I am using the 
GeneralParticleSource to create positron emitting point sources and 
examining their the distance that these positrons travel prior to 
annihilation with electrons in a tissue like material.   I also want to 
utilize a uniform transverse magnetic field to see how the field alters
the distance the positrons travel.  The distance should be reduced, 
because the magnetic field will cause the charged particles to spiral 
inwards due to the transverse nature of the field. 

For the magnetic field code I have used the 
and found in example field01 

Everything compiles, links, and runs beautifully.  The problem is that 
I do not believe that the magnetic field is taking any effect.  I know 
I have introduced a magnetic field because the simulation is hard coded 
to print out the magnetic field paramaters.  These are the paramaters 
that were printed:

PreInit> /control/execute

F01FieldSetup: magnetic field set to Uniform( 0, 0, 9.4 ) 

EpsilonStep: set min= 1e-05 max= 0.0001

G4ClassicalRK4 (default) is called

The minimal step is equal to 0.01 mm

The Box is 2 m   of Tissue

PhysicsList::SetCuts:CutLength : 1 mm 

To simplyify a test of the magnetic field's effect, I use the following 
macro file to shoot monoentergetic positrons:

/pr/det/setMat Tissue
/pr/det/setSize 2 m
/process/eLoss/verbose 1
/tracking/verbose 1
/pr/stepMax 6 mm
/gps/particle e+
/gps/ene/type Mono
/gps/ene/mono 4 MeV
/gps/direction 1 0 0
/run/beamOn 1 

I do this with both the field set to 0 Tesla and then 9.4 Tesla and I 
change nothing else.  The outputs are identical.  The track length, 
ending position in x-y-z, and range of the particles are the same.  
This indicated that the effect of the magnetic field is not being 

I intend on shooting ions using the gps commands, but it is easier to 
test the magnetic field via positrons for now.

Do you have any suggestions or assistance that can help in this matter.
I have been working on getting this magnetic field to operate properly
for weeks.  I sincerely appreciate any input you may provide.

Matthew Middione  

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1 Feedback: Re: Magnetic Field from field01 Example   (Tatiana Nikitina - 27 Sep, 2007)
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