[gate-users] point source

[Uday Tipnis]

Hi everyone,

I am trying a very simple simulation in Gate and am getting some 
anomalous results. I am using two planar detectors - simulated as 
a cylindricalPET system. The detector heads are 180 degrees apart 
i.e. they face each other. The distance between them is 41 cm. My 
source is a back-to-back gamma point source at 511 keV. When I 
simulate this source at the center between the detector faces 
(x=0, y=0, z=0) then I see what I expect in the projection data.

But if I shift this point source toward either of the detectors 
then the following happens: In the projection data I see one point 
source where I defined it and a second point of reduced intensity 
exactly axially opposite to the one I defined i.e. if I define my 
point source at x=10, y=0, z=0 then I see two points: one at x=10, 
y=0, z=0 and second at x=-10, y=0, z=0. The second point should 
not exist but I checked all the parameters and everything seems ok 
to me.

Anyone have a clue why this might be or have encountered this 
before please help.

Thanks in advance.
Uday