[Gate-users] Random coincidences count rate

[Josep F. Oliver]

Dear Tahereh,

The missmatch can be due to several reasons. I do not know the details
of your simulation. For instance, depending on how you implement your
sorting method it may lack a factor two in the formula, ie.   2*(delta
t) * N1 * N2.

In any case, the method your using (Singles Rate) is based on some
approximations that may not hold on your particular scenario. In
general, the SR method tends to systematically overestimate the correct
randoms rate, thus, finding some level of desagreement between the
correct randoms rate (as extracted from gate) and the SR estimation is
expected. Depending on your imaging device, source distribution, source
activity, etc... the desagreement may well range between 5-20%.

I hope this helps

-- 
____________________________________________________________
 Josep F. Oliver, Ph.D.

    CSIC - Consejo Superior de Investigaciones Científicas

    Tel.:     +34 96 354 37 20
    email:    oliver at ific.uv.es

      IFIC - Instituto de Física Corpuscular
      Edificio Institutos de Investigacion
      Apartado de Correos 22085
      E-46071 Valencia
      Spain 

____________________________________________________________



Tahereh Niknejad wrote:
>
> Dear gate users,
>  
> In the coincidence output, if enevntID1 is not equal to enevtID2, it
> will be considered as random coincidences. The number of random
> coincidences calculated in this way is not equal to   (delta t) * N1 *
> N2. (N1 and N2 are singles count rates and delta t is coincidence time
> window).
>  
> I have two detector plates in coincidence. So, values assigned to  N1
> and N2 are the total number of singles divided by 2.
>  
> Does anyone know why it happened?
>
> -- 
> Tahereh Niknejad
>
> PhD Candidate
> LIP - Laboratory of Instrumentation and Experimental Particle Physics
> ------------------------------------------------------------------------
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