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

[Sebastien JAN]

Hi Yuxuan,


Just for information:
e+e- annihilation is managed by the G4eplusAnnihilation class and in 
many cases, all annihilations are simulated with the AtRestDoIt() method.
This method performs the e+ e- annihilation when both particles are 
assumed at rest and it generates two back to back photons with energy = 
electron_mass.

Just to give you a part of the code :

The kinetic for the first gamma is the following :
---------------------------------------------------

aParticleChange.AddSecondary( new G4DynamicParticle (G4Gamma::Gamma(),
                                             Direction, electron_mass_c2) );


and for the second gamma :
--------------------------

aParticleChange.AddSecondary( new G4DynamicParticle (G4Gamma::Gamma(),
                                            -Direction, 
electron_mass_c2) );




Clearly, you can see that we have a back to back emission with 511 kev 
for each gamma.

Cheers
Seb


yuxuan.zhang at di.mdacc.tmc.edu a écrit:
> 
> 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
>  >
>  >
>  > ------------------------------------------------------------------------
>  >
>  > _______________________________________________
>  > gate-users mailing list
>  > gate-users at lphe1pet1.epfl.ch
>  > http://lphe1pet1.epfl.ch/mailman/listinfo/gate-users
> 
> _______________________________________________
> gate-users mailing list
> gate-users at lphe1pet1.epfl.ch
> http://lphe1pet1.epfl.ch/mailman/listinfo/gate-users
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> gate-users mailing list
> gate-users at lphe1pet1.epfl.ch
> http://lphe1pet1.epfl.ch/mailman/listinfo/gate-users