[Gate-users] Re : unwanted scatter events in primary spectrum

[Samuel BURG]

Many thank for those informations.

I will check Nist Xcom (a second time, I have already had one first look, but I 
can have miss something).
In fact I have 2 main "abnormal" spikes : one double around 70KeV and one around 
110KeV.

what did you mean by "aperfect crystal" in Gate ?

"you can't just filter it out with the Gate release"
you mean by a root post processing or with a dedicated Gate instruction (I don't 
see witch one ?).

sorry for my maybe dummy questions.


bestr regards,

Samuel




________________________________
De : Jan De Beenhouwer <jan.debeenhouwer at ugent.be>
À : Samuel BURG <samuel_burg at yahoo.fr>
Cc : Gate User List <gate-users at lists.opengatecollaboration.org>
Envoyé le : Mar 31 août 2010, 10h 24min 45s
Objet : Re: [Gate-users] unwanted scatter events in primary spectrum





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>