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Question Positron annihilation coordinates 

Forum: Event and Track Management
Date: 08 Mar, 2013
From: Ottavia <Ottavia>

Hello,

I'm new to Geant4 and I'm having a problem in simulating the distribution of the positron annihilation point around the radioactive source.

I've placed an atom of a radioactive element that decays via beta decay (such as F18) in the center of a sphere of water.

The things I'd want to have are the coordinates of the annihilation point and I tried to obtain them in the following way:

in the SteppingAction.cc I've asked to get the coordinates of the end of the step if the process that defined the step is actually the annihilation:

if(step->GetPostStepPoint()->GetProcessDefinedStep()->GetProcessName()== "annihil")

  {position = step->GetPostStepPoint()-> GetPosition();}

The problem is that if I perform a histogram of the number of the events with respect to the radius (computed as the module of the annihilation position vector) I always get a cusp-like function (which is what I expect) but with a sort of a depression around R= 0.5 mm, irrespective of the kind of element (F18, Ga68, etc...).

What is the reason for such behavior? Is this the right way to look for positron annihilation coordinates?

Thanks in advance,

Ottavia

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1 Feedback: Re: Positron annihilation coordinates   (Gumplinger Peter - 08 Mar, 2013)
(_ Question: Re: Positron annihilation coordinates   (Ottavia - 12 Mar, 2013)
1 Note: Re: Positron annihilation coordinates   (Ottavia - 12 Mar, 2013)
2 Feedback: Re: Positron annihilation coordinates   (Gumplinger Peter - 12 Mar, 2013)
3 None: Re: Positron annihilation coordinates   (michel maire - 13 Mar, 2013)
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