Integration time and radioactive sources

Dear colleagues,

I’m simulating the response of Si-Timepix3 detector to Bi214 source. It decays to Po214 through beta- decay and then to Pb210 through alpha decay. Lifetime of Bi214 is about 20 min and Po214 – 164 us.
So, I putted cutoff_time = 1200s int the config of DepositionGeant4 module.

From MC particle object I can see both electron and alpha:
#evNo #particle_id #process_id #mc_particle_is_primary #deposited_energy_mc_all mc_particle->getGlobalTime() #mc_particle
25 11 6 1 563.377 0.0238628 0x5637750bea00

25 -12 6 1 8.61774e-06 0.010715 0x5637750be940

25 22 6 1 1.34901e-05 0.0323883 0x56377431ef30

25 1000020040 6 1 7686.8 209766 0x56377431eff0

But, alpha particle is not connected with pixel charge (pixel_charge->getMCParticles()), just electron. Also, there are no induced charges on pixels from alpha particle.

If I putted integration time in GenericProagation module from 100 ns to e.g. 500000ns, pixel can “see” these alphas.

It means that charges are not propagated after 100 ns after the first decay of isotope, because alpha appears in this particular event after 209766 ns.

Is it the correct understanding?

Thank you in advance!

Best regards,

Hi @psmolyan

yes, your analysis is completely correct. We do take into account the time at which charge carriers are generated by a particle, also for the integration_time cut-off. The reason for this is that time-resolved simulations should also be able to show overlapping pulses from successive particle passages.

(Relevant code is here: src/modules/GenericPropagation/GenericPropagationModule.cpp · master · Allpix Squared / Allpix Squared · GitLab - key here is to sum initial_time_ and the time from the actual propagation when comparing to the integration_time parameter.)

Of course in your case with a 20min delay this is a bit extreme. If it still works fine with you by increasing the integration_time accordingly, I would suggest we keep it as is. I fear that adding (yet) another configuration parameter to ignore the time of energy deposition might create more confusion than help in most cases.

Let me know what you think!
Best regards,

Dear Simon,

Thank you for the explanation!

I guess, it is ok for me: I can reduce the integration time to normal values because I can get the time of alphas arrival and their positions from MC particle, and energy deposition from alpha is well known. Then I can artificially reconstruct the alpha cluster.

Best regards,

That works - of course you can also just keep the integration time that long, in your case there should be no drawback to that solution.