[Gate-users] unwanted scatter events in primary spectrum

[Jan De Beenhouwer]

Hi,



On 31 Aug 2010, at 00:47, Samuel BURG wrote:

> 
> 
> Hi Gaters,
> 
> 
> I have a crazy issue with scattering and primary spectra (SPECT simulation with 
> Tc99m)
> 
> when I create a primary spectrum from root data save from a gate simulation 
> there are to many events out of the dedicated energy spike, and it look like 
> event tagged as primary events are in fact scatter events.
> 
> this occurred in numerous different situations/configurations. I haven't find 
> any configuration who doesn't produce such a problem, even with the SPECT 
> benchmark.
> 

There is a small amount of fluorescence in the crystal. If you don't have a perfect 
crystal, then those photons will partly escape. It results in a peak somewhere around 100kev.


> here's all what I have tested, nothing solving the issue :
> - 32 / 64 bits arch
> - single CPU / SMP / Cluster
> - GATE version 4.0 / 5.1
> - source shape : point / cylinder
> - collimator : with / without
> - PMT back compartment : single volume / complex multi volumes
> - disabling all  non-crystal volume (setting all material to "Air", or removing 
> all volumes from simulation)
> 
> - different energyCut
> - crystal material : NaI / NaI(Tl)
> - with very basic digitizer (only adder) or very complex digitizer (all SPECT 
> modules but optic tracking)
> - same issue with the benchmark (root output and ASCII output)
> - same results using different fields of the root file to asses with event is 
> primary or scatter : RayleighVolName, RayleighPhantom, RayleighCrystal, 
> comptVolName, comptonPhantom, comptonCrystal
> 

If it is fluorescence, you can't just filter it out with the Gate release. Check the x-rays for your crystal on Nist Xcom and
you'll find the peaks in your spectrum.

Regards,
Jan



> Software versions :
> OS : GNU Linux, Ubuntu 10.4 LTS, x86_64
> GATE : 4.0 & 5.1
> root : 5.20/00      24 June 2008
> clhep : v2.0.3.2
> geant4 : 4.9.1.p02
> gcc : 4.2.x (replacing system default 4.4.x)
> 
> What's crazy is that in the sample file 
> gate_v4.0.0/benchmarks/benchmarkSPECT/Results_benchmark.doc the primary spectrum 
> looks like a primary  spectrum, and when I run the benchmark, the primary 
> spectrum has some additional scatter event !
> 
> So, there is something I really don't understand here, and it turns me crazy !
> 
> Attached :-> too big files, not attached, use sendspace links below
> - the outputs of the SPECTbenchmark compressed with 7z, ascii files and root 
> files.
> - screen capt. of the sprectra I have with my own processing and with the root 
> processing of the benchmark (root output)
> - results of the processing of ASCII output
> 
> someone has an idea before I break down ?
> 
> Best regards,
> 
> Samuel
> 
> Link for files on sendspace (ask me if you have any trouble downloading the 
> files):
> http://www.sendspace.com/file/vo7sa0 
> http://www.sendspace.com/file/0ofue2 
> http://www.sendspace.com/file/nvw4ef 
> http://www.sendspace.com/file/w1m0va 
> http://www.sendspace.com/file/seshz9 
> http://www.sendspace.com/file/xck3rt 
> 
> -----------------------------------------------------------
> Samuel Burg
> 
> 
> Mail : <samuel_burg at yahoo.fr>
> -----------------------------------------------------------
> "Aw, come on, who would be so stupid as to insert a cast
> to make an error go away without actually fixing the error?"
> Apparently everyone. 
> -- Raymond Chen  --
> -----------------------------------------------------------
> 
> 
> 
> _______________________________________________
> Gate-users mailing list
> Gate-users at lists.opengatecollaboration.org
> http://lists.opengatecollaboration.org/mailman/listinfo/gate-users

--
dr. ir. Jan De Beenhouwer
Ghent University - IBBT
IBITECH - MEDISIP
De Pintelaan 185
Block B - 502a
B-9000 Ghent
Tel. +32-9-332.02.58
Fax: +32-9-332.33.90
E-mail: <Jan.DeBeenhouwer at UGent.be>