[Gate-users] Sudden drop in recorded coincidences

[Ida Häggström]

Hello Uwe and thanks for your reply!

Yes, I'm using Mersenne Twister generator with an automatic seed. I
completely redid the simulations after the "drop boundary" with new seeds
(auto again), and got the same results, i.e. again there was much less
coincidences (about a factor 2.4 less). Looking in my raw text files (all
40 files) I also noticed that the scattered fraction (on total) is about a
factor 1.8 different from before and after the "drop boundary" (~3% before,
~5.3% after). The same goes for random fraction (~0.9% before, ~1.6%
after).  I really have no clue what can be causing this as nothing is
changed with the setup. As you also mentioned, I've never seen this
phenomenon before when I've only done up to 30 min aquisitions, only now
for longer ones.
/Ida

On Tue, Nov 8, 2011 at 11:54 AM, Uwe Pietrzyk <u.pietrzyk at fz-juelich.de>wrote:

>
> Hi Ida,
>
> we are having similar problems, that when running long productions,
> there is a sudden decrease in rate and length of root file. Actually, the
> run stops.
> Starting with the seed given in the GATE output, this can be reproduced.
> The effect
> appears on 32 and 64 bit systems, as we tested on different MAC-Systems.
>
> Our suspicion was the random number generator and we are now
> switching from Ranlux64 to MersenneTwister, but this needs further
> investigations. From your attached files I understand that you used
> the MersenneTwister (is this correct??), which we hoped would solve
> the problem.
>
> Kind regards,
>
> Uwe Pietrzyk
>
> On 08.11.2011, at 11:05, Ida Häggström wrote:
>
> Hello!
>
> I'm simulating a static, homogenous cylinder (F-18) for a 0-3600 sec
> acquisition time. I've created a bash script that portions the simulation
> onto 40 different processors. I've not included physical decay in my
> source, so I simply divide the simulation time into 90 sec acquisitions,
> i.e. the first processor simulates acquisition between 0-90 sec, the second
> 90-180 sec and so on up to 3510-3600 sec (yielding 40 root-files). My
> problem is that between the acquisition 2250-2340 sec to the one 2340- 2430
> sec, there's a sudden drop in recorded coincidences (the later root-files
> are less than half in size)! I use the exact same setup for everything
> (camera, phantom, suorce etc), the only thing I change is the start and end
> time of the dynamic aquisition (as well as the output file names of
> course).
>
> I've attached an image of the recorded coincidences vs. time for the entire
> 0-3600 aquisition where the drop is obvious. I also attached the raw image
> text files, and logs for the Gate-run for the two border aquisitions. Any
> input is appreciated! Thanks!
> Ida
>
> ----------- Aliases I send to the macro from my bash-script -------
> /control/alias StartTime "2250"
>       <----- For the other file, this is "2340"
> /control/alias EndTime "2340"
>      <----- For the other file, this is "2430"
> /control/alias RootOutputName "rootOutput_Prompts_t2250-2340" <----- For
> the other file, this is "..._t2340-2430"
> /control/alias RawOutputName "rawOutput_t2250-2340"                <-----
> For the other file, this is "..._t2340-2430"
> /control/alias unstableflag "false"
> /control/alias activity "1000000"
> /control/alias halfz "125"
> /control/alias fullz "250"
> /control/alias radius "100"
>
> ----------- Part of main macro
> -------------------------------------------------
> #  S T A R T   A C Q U I S I T I O N
> #
> /gate/application/setTimeSlice     1.  s
> /gate/application/setTimeStart     {StartTime}.  s
> /gate/application/setTimeStop      {EndTime}. s
> /gate/application/startDAQ
>
> ----------- Source macro
> --------------------------------------------------------
> #     S O U R C E
> #
> /gate/source/addSource twogamma
> /gate/source/twogamma/setActivity {activity} becquerel
> /gate/source/twogamma/setType backtoback
> /gate/source/twogamma/gps/particle gamma
> /gate/source/twogamma/gps/energytype Mono
> /gate/source/twogamma/gps/monoenergy 511. keV
> /gate/source/twogamma/setForcedUnstableFlag {unstableflag}
> /gate/source/twogamma/setForcedHalfLife 6586.2 s #Fluor-18
>
> /gate/source/twogamma/gps/type Volume
> /gate/source/twogamma/gps/shape Cylinder
> /gate/source/twogamma/gps/radius {radius} mm
> /gate/source/twogamma/gps/halfz {halfz} mm
> /gate/source/twogamma/gps/centre 0. 0. 0. mm
> /gate/source/twogamma/gps/angtype iso
> /gate/source/twogamma/gps/mintheta 0. deg
> /gate/source/twogamma/gps/maxtheta 180. deg
> /gate/source/twogamma/gps/minphi     0. deg
> /gate/source/twogamma/gps/maxphi   360. deg
> /gate/source/twogamma/gps/confine NULL #phantom_P
>
> #/gate/source/twogamma/visualize 5000 red 2
> /gate/source/list
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>
> /----------------------------------------------------------------------
> Prof. Dr. Uwe Pietrzyk
> Diplom-Physiker
> Institut für Neurowissenschaften und Medizin / INM-4
> Forschungszentrum Jülich GmbH
> 52425 Jülich
> Tel: +49-2461-61 4763
> Fax: +49-2461-61 2820 + 8229
> Mobil: +49-162-103-4871
> eMail: U.Pietrzyk at fz-juelich.de
> http://www.fz-juelich.de/inm
> &
> Bergische Universität Wuppertal
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> Fax: +49-(0)202-439-2811
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> ----------------------------------------------------------------------/
>
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