[Gate-users] (again) Energy Distribution and positron annihilation

Emmanuel BRARD emmanuel.brard at iphc.cnrs.fr
Fri Feb 18 10:05:08 CET 2011

Dear Gate Users , 


I am indeed using a water filled phantom and this might be why I get
annihilation inside the detectors elements, especially because this PET
system is dedicated to small-animal imaging and there the detector and very
close to each other. 

You said your simulations showed a maximum annihilation distance of 2 cm
which seems pretty huge to me for a positron. Were your simulation done with
Gate, Geant4 or any other Monte Carlo package ? I have no granted access to
any database regarding positron interaction, yet for an electron at about 1
Mev (which is higher than the max 0.6 Mev of a 18-F disintegration) and
according to NIST ESTAR database the mean range is less than 1 cm so I would
say it is less for a positron since the cross section should be higher for
anti-particle. This is a bit of an awkward comparison I admit though. 


Best Regards,



BRARD Emmanuel 

emmanuel.brard at alumni.u-psud.fr

Medical Physics - PhD Student

IPHC IMABIO Bat 25 - 23 rue du Loess

67037 Strasbourg Cedex 2



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