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Question Question re stopping power of lead 

Forum: Event and Track Management
Date: 07 Sep, 2011
From: Neil Fazel <Neil Fazel>

Hello, I'm working on the simple problem of determining how many electrons of a given energy entering at one end of a lead cylinder exit at the other end. To do this, in a run with N electrons (/run/beamOn N), I count the number of electrons stopped in the lead. I do it using this snippet of code in my UserSteppingAction() method:

  if (aStep->GetTrack()->GetTrackID() == 1 && 
      aStep->GetPreStepPoint()->GetPhysicalVolume()->GetName() == "Lead" && 
      aStep->GetPostStepPoint()->GetPhysicalVolume()->GetName() == "Lead" && 
      aStep->GetTrack()->GetKineticEnergy() == 0)
    eventaction->HasStopped(true);

So at every step belonging to a primary particle (Track ID = 1), if the step started and ended in the lead and the final kinetic energy was 0, I increment the count of stopped electrons.

The results show that as the lead thickness is increased, an increasing fraction of electrons are stopped in the lead, as expected.

However, for the same thickness, with increasing energy I get an increased fraction of electrons stopped; at almost any thickness between 10 and 50 mm, a lower fraction of 0.2 GeV electrons is stopped than any of the higher energies. This doesn't make sense to me. (I have attached a graph of the fraction of stopped electrons for energies between 0.2 and 3 GeV.) Any I doing something patently incorrect here?

Thanks, Neil

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2011/09/07/10.09-66511-stopping_power_of_Pb.png

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1 Feedback: Re: Question re stopping power of lead   (Neil Fazel - 10 Sep, 2011)
(_ None: RE: Question re stopping power of lead   (Penny, Robert D. - 11 Sep, 2011)
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