Incorrect 232Th decay chain

_Geant4 Version:_10.7.4
_Operating System:_Ubuntu 20.04
_CMake Version:_3.16.3

I am trying to obtain the gamma spectrum of the full 232Th decay chain (till Pb 208) using two HPGe detectors placed opposite each other.

I am getting reasonable results for the Co60 ion (first image). However, I am getting a super strange result for 232Th (second image), deposited energies go up to 40 MeV.

The macro file

/gps/particle ion
#/gps/ion 27 60
/gps/ion 90 232
# any position plus 6.32 cm
#/gps/pos/centre 0 0 6.32 cm
/gps/pos/centre 0 0 0 cm
#/gps/ene/type Gauss
/gps/pos/type Point
/gps/ang/type iso

/run/printProgress 1000
/run/beamOn 10000

Can someone please help where I am messing, I am a beginner to the radioactive decay in Geant4. Most of the earlier discussion here dealt with stopping the decay chain at a given nuclide, but for my task, we require the full chain.

Any assistance in this regard will be very helpful, Thanks in advance!

Below, a macro for example rdecay01, its printout, and the plot of the total visible energy, eg: total energy released except neutrinos.

n.b. in the macro kit.mac, the command thresholdForVeryLongDecayTime is necessary, but not essential for this plot.

kitu.mac.txt (284 Bytes)
kitu.out.txt (12.8 KB)

1 Like

Dear Maire, thanks a lot for your response and for sharing the plot of total visible energy.
However, can you please share if it is possible to get the gamma spectra of all the subsequent decays starting from Th 232 decay?
I am trying to simulate something like the below spectra
Th232 Gamma Spectrum
Thank You!


The example that @marie mentioned also provide an output with histograms for gammas, electrons and other interesting properties of the decay.

You can find the code under $G4INSTALL/share/Geant4/examples/extended/radioactivedecay/rdecay01

Or here


Dear Alvaro,

Oh sorry, yes it does. Thanks for pointing this out.

If i am right, this example doesn’t simulate detector response. Can you suggest a decent example that shows how to find the energy deposited by gammas in a scintillator from radioactive decays, probably (I only aware of rdecay02 and B3 to some extent) ?

Thank You!

I just answered to that on your other thread :slight_smile:

Okay, thanks.

Actually, I had a quite similar setup (except that did scoring using the class by defining a scoring volume as in example B1)
However, when I try the radioactive decay of Th232 I am getting clearly the wrong spectra. I am not sure if the issue is with how I am depositing and scoring the energies. Interestingly, it works fine with the cobalt 60.

I will try again with example B4c and see if it works.

Thank You

when using the custom stepping, were you running in multithread or SerialOnly mode?

I was running the simulation serially, only.
I think probably the hint to issue is discussed in this thread. But the problem is I am not aware of how to as discussed in the thread

apply a time cut (corresponding to your device’s trigger window) in your stepping action. If you’re recording the individual hits directly into an N-tuple, make sure you include the time stamp and you can apply that cut in your analysis.

do you mean record the global time when the decay happened?


Also, can you please share
1.) how can I kill all the radioactive secondaries from the mother nucleus to prevent them from further decay ( If I want to simulate the spectrum by simulating each nuclide in the decay chain separately)

2.) Apply a time cut (corresponding to your device’s trigger window) in the stepping action as @mkelsey suggested in the thread.

Sharing the code as well if it can help.

Thank You


I am unable to find the command (Geant4 10.7.4)

/process/had/rdm/thresholdForVeryLongDecayTime 10e+20 y

is it the same as ?


This time limitation did not yet existed in 10.7; remove this command


For the first, you can use the UI command /process/had/rdm/nucleusLimits as in the example here.

You may try to compare Geant4 simulation of energy deposited and efficiency with your experimental data before going into more detailed description such as including timing of your detector.


Thanks a lot, @atolosad and @maire for your valuable replies. I am away from the project for a while so did not get a chance to try them.

I will try implementing your suggestions.

Thank You