How to block the Decay of a Particle

Dear everyone,

I am interested in performing experiment simulations involving excited nuclei with geant4v10.07.02 . The point is that gamma rays emitted after the decay of an excited nuclei are affecting the simulated spectra, so I would like to block the decay of this specific nucleus.

Any clue on how to do this?

Thank you,


We have similar issues when simulating activation backgrounds in our experiment. There are two issues here relating to real life, which really determine what you should simulate:

  1. Do you excited nuclei remain embedded in your detector (for example, we have neutron activation in semiconductor crystals, so the activated nuclei stay there forever)? Or are you doing an atomic beam study, where the excited nucleus “goes away” quickly?

  2. What is the timescale for your data collection? Are you exciting the nuclei and recording their spectra immediately? Or do you have an integration time which is comparable to the half-life?

In those cases, the decay spectra, or some part of it, will be part of your data in real life, so including it in the simulation will help you with your experimental design. If you record the individual energy deposits (as an N-tuple), you can include the hit time, and apply appropriate cuts to your data during analysis.

Having said that, there are various ways to restrict what the simulation does in your case. If you don’t need any radioactive decay at all, you could turn it off completely:

/process/inactivate RadioactiveDecay  (or RadioactiveDecayBase)

If you want to limit decays to just your main nucleus, and not the whole decay chain (we do this with our Cf-252 neutron source for instance), you can use

/process/had/rdm/nucleusLimits [Amin] [Amax] [Zmin] [Zmax]

Only nuclei within the specified range will be decayed.

Thank you very much for your answer.

What ended up working for me was to turn off the Decay option in the “PhysicsList” file of the simulation environment, since there was only one gamma decay taking place.