Hi everyone I am trying to understand the propagation of charges by measuring the initial and final charge cloud generated at impact and at collection. I am using the GenericPropagation and taking the distances between charge particles using the DepositedCharge and PropogatedCharge objects. I wanted to know why the final diameters of Am241 and Co57 were similiar with both a 2mm and 5mm thick CdTe sensor.
This leads me to ask… Is the diffusion independent of the initial charge cloud size? Is the diffusion just a multiplying factor that is applied at each motion integrated point?
Thanks!
Hi, I encountered a problem very similar to yours.
When APSQ call Geant4 for energy deposition simulations, it won’t set the initial distribution for carrier generation, so carriers start diffusing from a single point instead of a charge cloud. This will significantly affect the carrier collection results for small pixel sizes like 15um.
@solomen I see, what was your solution to account for a charge cloud shape with smaller pixels? Did you use the DepositionPointCharge module? Or did you simulate the charge cloud generation in Geant4 and imported that into Allpix?
Thanks!
In fact, I identified this issue just last week. And I also found spot_size in DepositionPointCharge module, but this solution will neglect other physical effects such as secondary emission deposition of K-shell photons.
I don’t know if G4 can simulate a charge cloud.
Overall, I have yet to find a perfect workaround. Hope the developers could give a hand.
Hmmm but when I get the spatial distribution of the deposited charges after a gamma ray interacts with the sensor I do get an initial distribution. Its just that the final diameters are close when I think they should not be. I assume that a lower energy gamma ray would penetrate less and have to diffuse more until charge collection at the anode. Therefore, the diameter should be larger for Am241 rather than Co57. Could it be that the diffusion happening is not dependent on the initial charge cloud created?
@simonspa Would you be able to comment on this?
