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<TITLE>RE: [Gate-users] low energy and standard mode</TITLE>
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<P><FONT SIZE=2>-----Original Message-----<BR>
From: gate-users-bounces@lists.healthgrid.org on behalf of Sanae Rechka<BR>
Sent: Wed 1/2/2008 11:19 PM<BR>
To: gate-users@lists.healthgrid.org<BR>
Subject: [Gate-users] low energy and standard mode<BR>
<BR>
<BR>
> Dear Gate users,<BR>
<BR>
> I would like to ask you please if it's better to use low energy mode or standard<BR>
> mode for 511 keV. I would like also to mention that according to the Hits<BR>
<BR>
The standard EM model is a parameterized model and is optimized to high energy application,<BR>
which guarantees a 5% uncertainty above 10 keV according to Geant4. There is no Rayleigh<BR>
scattering process implemented in the standard model since its cross section in high energy region<BR>
is very low.<BR>
<BR>
On the other hand, the low energy model is a data-driven model which utilizes the measured cross section<BR>
data for photoelectric, Compton, Rayleigh processes (G4EMLow data lib). This model gives more precise<BR>
results in low energy region.<BR>
<BR>
For 511 keV, there is not much difference with two models especially for photoelectric process, but the standard model<BR>
is more computing-efficient.<BR>
<BR>
> output file generated, when using the standard mode the energy deposited by<BR>
> Compton interaction is 0 which is normal. But when using the low energy mode<BR>
> there is some energy associated to Compton interaction, in this second case<BR>
> what does this energy represent ?<BR>
<BR>
<BR>
Do you have such an energy distribution plot?<BR>
What is your Geant4 and G4EMLow versions?<BR>
<BR>
If possible, can you compile different G4EMLOW v3 or v4 into the same Geant4, GATE version to see any difference?<BR>
<BR>
Yu<BR>
<BR>
> Thank you<BR>
<BR>
> Happy new year too<BR>
<BR>
> Sanae<BR>
_______________________________________________<BR>
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Gate-users@lists.healthgrid.org<BR>
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<BR>
<BR>
<BR>
Yu Chen, Ph.D.<BR>
University of Massachusetts Medical School<BR>
Division of Nuclear Medicine<BR>
55 Lake Avenue North<BR>
Worcester, MA 01655-0243<BR>
Phone: (508) 856-6123<BR>
Fax: (508) 856-4572<BR>
<BR>
<BR>
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