[Gate-users] Problem with the coincidence

[Simon Stute]

Hi,

2010/4/19 Jinxia Guo <jinxia.guo2009 at gmail.com>

> Dear gate users,
>
> I encountered a problem when I inspection the time difference of two
> singles
> in a coincidence. In the simulation, there are many coincidences in which
> the time difference of two singles is larger than the coincidence window. I
> do two simulation. In the first one, the time resolution is set to 200ps
> and
> the coincidence window is set to 200ps. In the second one, the time
> resolution is set to 0 and the coincidence window is set to 200ps. In both
> simulation, the problem exists. I can't find why this happened with
> chapter8
> of GATE user guide. So who know how gate does its coincidence？Why the time
> difference of singles in coincidences is larger than the coincidence
> window?
>
>

You can plot the time difference, in order to have an idea of what the
problem really looks like, it would be a good start.
For example to see if you have a sort a gaussian function, or a dirac
function at a certain time difference value, it would be easier to try to
understand the problem.
And to study the problem, just set the time resolution to 0, otherwise it
would be too difficult to analyse the results.



> In addition to the above simulation, I do another two simulation. In first
> one, the time resolution is 300ps and coincidence window is 10ns. In second
> one, the time resolution is 300ps too and coincidence window is 100ns. I
> found there are more coincidences in the first simulation than in the
> second
> simulation,about five times larger.Then who can explain it？
>
>

By setting your time window to 100ns, you will have a lot of multiple
coincidences, so it depends on what policy you choose.
By default, takeTheWinner is chosen, so it explains why you get five times
less coincidences in your second simulation.
See the user's guide.

Cheers,
Simon


> By the way, in all simulations, the diameter of simulated PET ring is about
> 82cm. And the simulation time is the same.
>
> Hope for help. Thank you!
>
> -
> Jinxia Guo
> School of Life Sci&Tech
> D11 Building Room 503
>
> Huazhong Univ. of Sci. & Tech
>
> 1037 Luoyu Road, Wuhan 430074, China
> Tel:+86-27-8779-2294
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