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Question Positron annihilation coordinates 

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


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 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,


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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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