Getting the decay counts per unit time?

Hi everyone,

I am trying to simulate a volumetric, 2cm by 2cm cylindrical 138 La source. I am using G4Ion and GPS for the model.

Can someone please suggest how to get the counts per second of this ion being registered in a detector placed at a fixed distance from the center of the cylindrical source? The main issue I am facing I think is how to go from events to the time the counts were being registered.

Thanks in advance!

This sounds like a repeat of an existing question?

What is the activity of your source (in units of curies or becquerels)? With that, you can directly convert events to time.

If you know the half-life and the number of La-138 atoms in your source (hopefully you don’t actually have a purified cube of La-138 in real life), then you should know how to translate that into activity. If not, you should know how to look it up.

Yeah, sorry for the repetition OI was confused earlier.

I estimated the activity of La138 (from La138 half-life and its abundance in the LaBr3 crystal).

The activity comes to be 196 bq and is supposed the source is “on” for 100 seconds, does it mean I need to simulate 19600 events in Geant4 to incorporate this activity into my simulations?

Can you please comment on above reasoning ?


If it so, then yes.

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Yes, you have it right. Keep in mind that Geant4 is a Monte Carlo (random) simulation. So you may want to generate a larger number of events, and divide them into “groups” of the 19,600. That way you can better estimate the uncertainty in your final results.

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Thanks Michael,

So, the uncertainty will go as 1/sqrt(N) where N is the number of groups containing 19600 events each ?