[Gate-users] Energy spectrum in simple CZT SPECT setup

[Simon Stute]

Hi Philipp,

You say you are looking at singles, but singles are formed from hits, and
hits (real interactions) are combined by an adder module to give singles.
So did you use at least an adder in the digitizer ?
Did you assigned a physics package to the compton and photoeletric effects ?
I don't know what is the default if you don't give the following commands
explicitly :

gate/physics/gamma/selectPhotoelectric    [lowenergy, standard, inactive]
gate/physics/gamma/selectCompton    [lowenergy, standard, inactive]
gate/physics/gamma/selectRayleigh    [lowenergy, standard, inactive]

5mm depth for your "crystal" is also sufficient, but try to put much more.

Hope this helps,
Simon


On Thu, Sep 30, 2010 at 10:31 AM, Philipp Matthies <
philipp.matthies at googlemail.com> wrote:

> Hello,
>
> I set up a very basic simulation with only a CZT crystal and a point
> source, nothing more. I'm using GATE v5 under Mac OS X.
>
> In the screenshot I plotted a few variables from the Singles tree of the
> ROOT output. Can anybody explain the energy spectrum to me?
> I didn't set any digitizer options and the source is monoenergetic
> (140.5keV) so I expected so see a clear photopeak at 140.5keV and the
> characteristic compton spectrum.
> Instead there appear like two peaks between around 105keV and 115keV and a
> few more at lower energies. No photopeak, no compton spectrum, nothing like
> I expected it to be.
>
> The setup was as followed:
> - world volume 20 x 20 x 20 cm^3 air
> - CZT crystal (4.0 x 4.0 x 0.5cm^3) set as sensitive detector
> - point source of 140.5keV and 1MBq at a distance of 5cm centered in front
> of the crystal
> - no digitizer
>
> For the whole script with all variables set see attached file
> G4History.macro.
>
>
> Kind regards,
>
> Philipp Matthies
>
> ---------------------------------------------------------
> Physics Department, TU Munich
> Nuclear medicine, Klinikum rechts der Isar, Munich
> SurgicEye GmbH, Munich
>
>
>
>
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