[Gate-users] variance in the number of optical photons produced per gamma interaction in PET

[Pedro Correia]

Thank you Vesna for your help!

I read the wiki page that explains the optical behavior, and I found the same information that you gave me, I should payed more attention the first time that I read that page.

About this, I forced the standard deviation to be zero. Is there any way that I can confirm that the number of produced photons is exactly the scintillation yield defined in the Materials.xml file, i.e. there is some root variable that tell me how much optical photons are produced due to scintillation, for each event?

Thank you again.
Best regards, Pedro


No dia 15/04/2014, às 15:04, Vesna Cuplov <vesna.cuplov at gmail.com<mailto:vesna.cuplov at gmail.com>> escreveu:

Hi Pedro,

Yes, when the gamma photon deposits 0.511 MeV in your LYSO crystal, then the number of emitted optical photons would be 0.511x28000 with a standard deviation of resolution_scale x sqrt{0.511x28000}. Could you send your geometry, materials and root file?

thank you
vesna



On Tue, Apr 15, 2014 at 2:42 PM, Pedro Correia <pmcorreia at ua.pt<mailto:pmcorreia at ua.pt>> wrote:
Dear Gate users

I’m simulating a cylindrical Pet, where my crystals are LYSO, with a light yield of 28000 photons/MeV, each one with ~ 3eV, and my source are gamma rays with fixed energy of 511 keV.

When I analise the root files, I saw that the actual number of hits of each detected interaction of 511 keV is not ~14000, as I would expect since 28000*0.511=14308. Actually, what I see in the root file is that some events produced ~10000 hits, while others produced ~15000.

Is this related with the random seed that I’m using for simulations? In my point of view, the number of hits per each gamma photon absorbed should be the same, for the same energy, am I wrong?

I can attach the root output if someone ask to.
Thank you all. Best regards.

Pedro Correia
PhD student
University of Aveiro




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