[gate-users] about the acolinearity of two gamma photons

[yuxuan.zhang at di.mdacc.tmc.edu]

Hi, Seb,

Thank you for your reply. I got these questions because
that from the gate.root we can see the acolinearity angle
distribution if the positron source are used, however, if
a isotope source was used, then we can not get the acolinearity
distribution from the gate.root output. 

In Geant4, there is one chapter describe the process of 
positron and electron annihilation, with can be found here:

http://wwwasd.web.cern.ch/wwwasd/geant4/G4UsersDocuments/UsersGuides/PhysicsReferenceManual/html/node43.html

>From this chapter, it seems that Geant4 will calculate the final states of 

the two gamma photons according to the kinetic energy of the positron,
which means the acolinearity should be included. But it also mentioned 
a method called AtRestDoIt, in that case the kinetic energy is taken as 0.
I am not quite familiar with Geant4, so I don't know what's the real 
model they are using in Geant4 for the e+e- annihilation. Maybe you can 
find it out by checking the source code.


Best regards,

Yuxuan




Hi Yuxuan,


>  1. If a backtoback gamma source is used, is the acolinearity be 
simulated?


No, the acolinearity class is called only for e+e- annihilation

>  2. If a isotope source is used, (F18, O15, etc), is the acolinearity be 

> simulated?

Yes, in this case the acolinearity is always simulated.


> but in the Physics Reference Manual of Geant4, the acolinearity should 
> be calculated in
> Geant4.


Could you send me the page where you have read this information in the 
G4 guide ? (or the class name which simulates this process)

Thanks
Seb


> 
> Anyone can give some explainations about that? Thanks.
> 
> 
> Yuxuan ZHANG
> 
> 
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