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Question Track Momentum Direction 

Keywords: Momentum Vector
Forum: Event and Track Management
Date: 18 Mar, 2007
From: Justin Dingley <>

Hello all!

I have a question regarding the output of the GetMomentumDirection function.
I have defined a non-interacting volume in my geometry for tracking bremsstrahlung
photon energy and angular distribution. The code snippet below shows how I 
get the kinetic energy and momentum vector of each photon entering the volume:

G4bool CheckVolumeSD::ProcessHits(G4Step* aStep, G4TouchableHistory*)
  const G4Track* track = aStep->GetTrack();
  if (track->GetDefinition()->GetParticleName() == "gamma") {
    e = track->GetKineticEnergy();
    G4ThreeVector m = track->GetMomentumDirection();
    //G4ThreeVector p = track->GetPosition();
    mx = m.x();
    my = m.y();
    mz = m.z();
    mm = sqrt(pow(mx,2)+pow(my,2)+pow(mz,2));
    angx = acos(mx/mm);
    angy = acos(my/mm);
    angz = acos(mz/mm);
  return true;

The question I have is about the reference point for the Momentum Vector-
is it in relation to the interacting electron vector at the point of photon
generation or something else entirely?

Thanks in advance,

Justin Dingley
Rensselaer Polytechnic
Nuclear Engineering

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1 None: Re: Track Momentum Direction   (Makoto Asai - 18 Mar, 2007)
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