[Gate-users] SPECT without collimator, issue with source?

[Maikol Salas Ramirez]

Hi Monika,

I faced a similar problem (in my case, for internal dosimetry). From my
point of view, there are two reliable ways to simulate a source: the *Ion*
description (Geant4/GATE intrinsic) and the ICRP 107 (
https://www.icrp.org/publication.asp?id=ICRP%20Publication%20107) as a
*userSpectrum*. Both source descriptors use the ENSDF database (
https://www.nndc.bnl.gov/ensdf/). The difference stays in how the data is
read; the ICRP 107 uses the software EDISTR04 to read the ENSDF database,
while GEANT4 has the physics processes: 1- G4PhotonEvaporation and  2-
G4RadioactiveDecay, where G4PhotonEvaporation is in charge of the photon
emission yields and G4RadioactiveDecay of the other particles (beta, alpha,
...).
The main difference that I found lay in the very low gamma emissions (in
the order of 10eV or less). I associated this difference with the EDISTR04,
which achieves a very detailed spectrum of x-ray and Auger electrons.
I recommend you to compare both sources Ion vs. ICRP 107. Also to check
your physics list. The 80 keV peak comes from the Ra-224 x-ray emission (
https://www.nndc.bnl.gov/nudat2/decaysearchdirect.jsp?nuc=224RA&unc=nds),
and I would expect that these emissions are included in both radioactive
source descriptors.

Best regards
Maikol


El mié, 6 oct 2021 a las 15:40, Monika Kvassheim (<
monikakvassheim at outlook.com>) escribió:

> Dear all,
>
> I have modelled a Siemens Symbia SPECT and obtain energy spectra
> consistent with experimental results with both a HE and a MELP collimator
> with a Ra-224 ion source. When I run the simulation without a collimator,
> the resulting energy spectrum matches the experimental result above 150
> keV. The main peak at 80 keV however, disappears. Please see the attached
> plot.
>
> I questioned whether the source was the issue and changed from an ion
> Ra-224 source to a userSpectrum. The result is also attached, I have a
> large 80 keV peak, but now the 240 keV peak is missing.
>
> I am very confused and hope someone can help.
>
> Best regards,
> Monika Kvassheim
>
>
>
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