[Gate-users] Positron range simulation - inconsistency between GATE 8.0/ 9.0 and between source types

[Minh Phuong Nguyen]

Dear GATErs,

I simulated positron ranges for several isotopes such as F-18 and I-124
with GATE. The setup was very simple with a point source at the centre of a
water environment (20-cm-radius sphere). The sphere was that large to make
sure that the positrons do not escape the water volume.

The obtained mean/max positron range from this simulation was shorter than
what I found in literature. Then I tested with different GATE versions
(8.0/ 9.0 with corresponding GEANT4 versions as stated in the GATE
documentation), and different ways of defining the source (ion, e+,
fastI124). I observed that the positron range result was not consistent
when changing these parameters (attached figures).

Looking at the range distributions (attached figures), GATE 8.0 with ion
source produced a lot of annihilations near the decay locations (range ~ 0
mm). This was not the case with GATE 9.0 and e+ or fastI124 sources.

Does anybody know:
- why positron range from GATE is shorter than in literature?
- which changes in the new GATE version makes the discrepancy in positron
range simulation result?
- what makes the difference in positron range between the ion source and
other type sources?

Thank you.
Kind regards,
Minh Phuong Nguyen
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