[gate-users] Very low number of scatter in GE Discovery

[Mikhail Shilov]

Dear Gate group,

I was investigating the fraction of scatter in GE discovery in normal
and in 3D mode ( no septa).
I ran a simple simulation (see the attached file) with 3 cylindrical
F-18 sources inside a 20 cm radius and 30 cm height cylindrical phantom
and recorded gateSingles.dat and gateCoincidences.dat files. I then
looked at the number of recorded coincidences with at least one Compton
scatter inside the phantom. It turned out that this number is ~0.5%
(~0.8% in 3D) of total recorded coincidences.
This is not what I would expect from the literature ( ~30%). The
fraction of singles is what I expected ~ 30%

I was wondering if anyone looked as this issue before and if my result
is reasonable.

Here is my digitizer script:

#       A D D E R
/gate/digitizer/Singles/insert adder
#       R E A D O U T 
/gate/digitizer/Singles/insert readout
/gate/digitizer/Singles/readout/setDepth 1
#      E N E R G Y   B L U R R I N G
/gate/digitizer/Singles/insert blurring
/gate/digitizer/Singles/blurring/setResolution 0.15
/gate/digitizer/Singles/blurring/setEnergyOfReference 511. keV
#       E N E R G Y   C U T
/gate/digitizer/Singles/insert thresholder
/gate/digitizer/Singles/thresholder/setThreshold 300. keV
/gate/digitizer/Singles/insert upholder
/gate/digitizer/Singles/upholder/setUphold 650. keV
#       D E A D    T I M E 
/gate/digitizer/Singles/insert deadtime
/gate/digitizer/Singles/deadtime/disable
/gate/digitizer/Singles/deadtime/setMode nonparalysable
/gate/digitizer/Singles/deadtime/chooseDTVolume block
#       C O I N C     S O R T E R 
/gate/digitizer/Coincidences/setWindow 12.5 ns
  

Mikhail A. Shilov
The Johns Hopkins University
Department of Radiology
Division of Medical Imaging Physics
Tel:   (410)502-3773
Fax:  410-614-1977
mailto: mshilov1 at jhmi.edu
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