[gate-users] WARNING : positron found and photonID vector size:1

[Giovanni Santin]

Hi Theo and Jin
I can confirm the remarks by Jin

You get these (warning) messages when the positron has not annihilated 
before reaching the World boundary.
This happens often when the source is in Air, as Jin suggested.
But having the source in Air is in most cases totally unrealistic, as it 
is normally contained in some liquid or solid. 

I would suggest to define the source geometry (volumes and materials) 
correctly (for both liquid and container) and to position the source 
accurately in it.

Due to the relatively low positron energy, most of the positrons will be 
stopped either in the liquid or in the (glass/plastic/...) container. 
Some can escape, so a few warnings are OK. in any case, the results will 
be realistic, as in the real experiment some positrons will escape as 
well.

Best regards,
-- 
Giovanni
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Giovanni Santin
Space Environments and Effects Analysis
ESA - ESTEC - TEC-EES
Keplerlaan 1, 2200 AG Noordwijk, Netherlands
e-mail: giovanni.santin at esa.int
Tel: +31 71 565 6267
Fax: +31 71 565 4999


On Mon, 3 Jan 2005, Jin Zhang wrote:

> Hi Theo:
> 
> Yes, I think to have electron range cuts would help but I doubt if the 
> simulation results would be very different. As I guess the warning means 
> that the positron is out of the camera's field of view and thus it's 
> annihilation photons would not be counted as coincidence events.  But 
> they do contribute to Random and Scatter counts though. Pls correct me 
> if I am wrong.
> My suggestion is that a few of these warnings would be OK, if you didn't 
> get tons of it, which reduces your actual activity dose.
> Good luck and I want to hear more about this as well.
> 
> Jin
> 
> Mutanga Theodore wrote:
> 
> >Hi Jin,
> >I did as you suggested and I still had some warnings, maybe I have to set
> >some electron range cuts instead ?
> >What do you think ?
> >Has anyone been doing measurements in air ?
> >Theo
> >
> >
> >
> >  
> >
> >>That is because of the much longer positron range in air, which is about
> >>170 cm for F18. But the average range in water is only 0.06 cm (F18). If
> >>you can use a small water sphere to hold your source, it may help to
> >>stop the warning message.
> >>
> >>Jin
> >>
> >>Mutanga Theodore wrote:
> >>
> >>    
> >>
> >>>Hello Gaters,
> >>>
> >>>I had a setup for simulating and measuring the resolution of the
> >>>scanner,since the measurements had to be done in Air, I defined a phantom
> >>>which is a cylinder the same size as the inner diamter of the scanner.
> >>>
> >>>When I set the material as Air I have this warning messages
> >>>
> >>>:[GateTrajectoryNavigator::FindAnnihilationGammasTrackID]  WARNING :
> >>>positron found and photonID vector size: 1
> >>>
> >>>I don't really know what this means but when I use Water as the medium in
> >>>the phantom I don't get this error , how does it affect my simulation ?
> >>>
> >>>Cheers
> >>>
> >>>Theodore
> >>>
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> >>>
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> >>
> >
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