[Gate-users] Energy spectrum in simple CZT SPECT setup (Simon Stute)

[Simon Stute]

Hi Philipp,

On Thu, Sep 30, 2010 at 3:23 PM, Philipp Matthies <
philipp.matthies at googlemail.com> wrote:

> Hi Simon,
>
> ah, that's a very good point and totally makes sense!
> I didn't set any digitizer modules, so I have set an adder module now and
> ran the simulation again and I could see a perfectly sharp photo peak.
>


OK good !



> And as you can see in the G4history.macro (didn't you receive the
> attachments?) I set the physics to be like that:
>
> /gate/physics/gamma/selectRayleigh lowenergy
> /gate/physics/gamma/selectPhotoelectric lowenergy
> /gate/physics/gamma/selectCompton lowenergy
> /gate/physics/gamma/selectGammaConversion lowenery
>


OK I just looked at the screenshot, and it is OK.



>
> I thought (obviously wrong) that the photoelectric effect would be one
> interaction, e.g. one hit.
>


I am clearly not an expert in particle physics ! so I let someone else
(maybe ?) explain you what really happens :-)

Cheers,
Simon



>
> Thanks a lot,
>
> Philipp Matthies
>
>
>
>
> Am 30.09.2010 um 12:00 schrieb
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> >  1. Re: Energy spectrum in simple CZT SPECT setup (Simon Stute)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Thu, 30 Sep 2010 11:04:02 +0200
> > From: Simon Stute <gate.stute at gmail.com>
> > Subject: Re: [Gate-users] Energy spectrum in simple CZT SPECT setup
> > To: Philipp Matthies <philipp.matthies at googlemail.com>
> > Cc: gate-users at lists.opengatecollaboration.org
> > Message-ID:
> >       <AANLkTikakHLDdgM7oJmbjxMDMCdRn=d2xX8iOe1c2GpJ at mail.gmail.com>
> > Content-Type: text/plain; charset=ISO-8859-1
> >
> > 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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