Metastable States Not Registered


I am examining the effects of neutron activation in materials. I have been simulating 2.45 MeV neutron interactions in xenon, and I have noticed that metastable states don’t appear to be properly registered. Take Xe131m for example: I would expect both “neutronInelastic” interactions on Xe131 and “nCapture” processes on Xe130 to potentially generate Xe131m. In looking at the event data, I do indeed see gammas at the appropriate energy level for Xe131m, but at no point is a particle with particle ID or name corresponding to Xe131m generated. Additionally, the gammas are listed as being created by the “neutronInelastic” or “nCapture” process, rather than any sort of decay of Xe131m.

I am currently using GEANT4 10.3, I have the NeutronHP physics list enabled, and I’m using the Binary Cascade model, but I’m wondering if there is some other physics I’m missing, or perhaps if there is missing cross section/decay data in the NeutronHP library that causes metastable states to remain unpopulated.

I’m by no means an expert with GEANT4, and while I did try looking through the G4NDL files as well as the source code for neutron and hadronic processes, but things started going over my head, and I didn’t immediately see what may lead to the generation of metastable states.

I did come across this topic, which seems to suggest that QGSP_BIC populates metastable states in neutron interactions, but not QGSP_BIC_HP, so that may be my problem.

Still, any help or definitive answer is appreciated! As well as pointers on suggested routes for getting the best results for neutron activation physics.

What’s the expected lifetime of Xe131m? Many of these states are handled internally by the de-excitation code within those proceses, rather than being exposed as tracks.

The lifetime of Xe131m is 11.84 days, but all the gammas are emitted immediately at the time of the inelastic/capture interaction. There’s no associated lifetime.

The two attached runs show that, with recent versions of Geant4 ( I do not remember exactly which one), metastable states are explicitly created, both by neutron capture or gamma excitation.
However this is true for QGSP_BIC physics, but not HP !
ncapture.mac.txt (292 Bytes)
ncapture.out.txt (2.0 KB)
gamma.mac.txt (254 Bytes)
ncapture.out.txt (2.0 KB)

sorry, last file was wrong file …
gamma.out.txt (1.8 KB)


I would suggest to switch to 10.6p02. As Michel mentioned, meta-stable levels become produced as tracks in 10.5 but there were problems with life time limits, which were fixed only recently.


Hi all,

Thanks for the feedback.

In your ncapture.out.txt file, I see

List of generated particles:
          Xe131:    8225  Emean =  98.675 eV 	( 22.286 eV  --> 188.64 eV )

But it looks like you generated 100k neutrons. I would have expected 100k resulting Xe131 particles, since it seems like they should all capture in your 100% Xe130 material. Why are there so few Xe131 atoms? And you said you saw Xe131m production, but I don’t see it in your output - did you truncate the output?

Do you meant that in 10.6.p02, even the HP physics list produces metastable levels as tracks, or is that still only with the non-HP physics list?

Thank you

I did not truncate output ! Xe131[163.930] is the second line.
I resend again the file.
ncapture.out.txt (2.0 KB)

Thank you - seems it was a strange issue with the text editor I happened to use to view it. I see the full output now.

Just wanted to ask one more time - did you mean that Geant4 10.6.p02 would produce metastable levels as tracks even when using the HP physics list?

I am using my collaboration’s framework that is built on top of Geant4, and so I can’t immediately use 10.6 to test things out, but I do think we are in the process of migrating to 10.6

Just wanted to ask one more time - did you mean that Geant4 10.6.p02 would produce metastable levels as tracks even when using the HP physics list?

No !


Ah, ok, so the output you generated was with 10.6.p02?

Edit: Nevermind, I see you say “recent versions of Geant4 (I do not remember exactly which one)”.

Thank you both for your help and input. It looks like I should stick with the HP physics list for better neutron handling, and then estimate metastable production from published cross-sections rather than trying to get it recorded in the simulation.