[Gate-users] Problem Evaluating Counting Rates - High Amount of Random Coincidences at High Activities

[Benedikt Rossboth]

Dear Gate Users,

after modeling my scanner more or less in the style of the biograph, and
the NEMA phantoms for Scatter Fraction and NECR, I started simulations
for getting the NECR. 

The progress of this graph seems right, with only one bad issue: 
The random coincidences are increasing far too fast. Hence the NECR got
the maximum with ~30kcps at about 20 kBq/ml instead of ~100kcps at 35
kBq/ml.

The coincidence window is set to 4.5 ns. 
The minimum sector difference is set to 12.


Any ideas how the random coincidences could be kept low even with higher
activities?
Is there anything which could decrease the randoms within the digitizer,
or is it more likely, that it is because of some wrong
scanner-geometries? 

best regards,
Benedikt Rossboth
UAS Technikum Vienna