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

[Samuel BURG]

Hello,

1)
>> 

>> 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.
>>

sorry if I say something stupid, but XCom-NIST is for photon cross section ?
how do we compute fluorescence from cross section / attenuation coef ?
maybe you where thinking of an other NIST data base? the "X-ray transition 
energies" database? the "XPS" database?


I alway get lost when searching the NIST web site ... to much tings there !

2)
If the solution of my question is fluorescence, then we really need to think of 
an update for the SPECT benchmark macro files and the post processing files 
samples send with gate releases, because it can be confusing.

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>