Fe‑56 captures a neutron and emits multiple gamma rays（each about 7.6MeV)

[dengmanna]

Hello!
I found a mistake in my simulation. In the simulation, I used the AmBe neutron energy spectrum as input and recorded neutron capture events on Fe‑56. However, I noticed some anomalies — a single neutron capture sometimes results in the emission of multiple gamma rays with energies around 7.6 MeV, which should not happen in reality. I would like to understand why this occurs and how I can modify my code to correct it.

I saw on the forum that this issue might be related to the PhotonEvaporation class, but I’m using version 10.6.2, in which this class cannot be used independently.

I would greatly appreciate it if you could help me resolve this issue!

_Geant4 Version:10.6.2
_Operating System: Linux
Compiler/Version:
CMake Version:
I record the deposition hit of each trackId.And part of the result are as follow.It indicates that there are four 7.6MeV gamma rays comes from the same parent.

[mkelsey]

"Duplicated" X-rays from electron capture decay?

Geant4 10.7.4, Linux, using CDMS simulation framework. One of our CDMS users is seeing some strange behaviour in Ge-71 decays. The decay process is via electron capture, with three characteristic lines corresponding to K (10.331 keV), L (1 keV), and M (100 eV) capture. However, my collaborator is seeing events with 20, 30, even 40 keV of energy coming from a single Ge-71 decay: [Ge71-extra-energy] From one of these events, we see a mix of X-rays (G4Gamma) and Auger electrons, which clearly…

We have seen similar effects, using Geant4 10.7.4 with G4ParticleHP, with neutron activation of our germanium detectors, i.e., Ge-70(n,gamma)Ge-71. We thought the problem was with RadioactiveDecay, since the gammas we see are consistent with the Ga-71 X-rays following Ge-71 electron capture. But the problem is not reproducible with rdecay01.

I agree that this is likely related to PhotonEvaporation. Tracing back from my post above, it’s possible that setting

export G4NEUTRONHP_USE_ONLY_PHOTONEVAPORATION=1

or

/run/initialize
/process/had/particle_hp/use_photo_evaporation true

might eliminate the duplicated gammas, at the cost of not getting the evaluated data intensities for the gamma lines. If your simulation only needs energy conservation, and not exact spectra, this may be an option.

[dengmanna]

Thank you so much for replying this!
I found your post yesterday,and in my macro file,I add

/process/had/particle_hp/use_photo_evaporation true
/process/had/particle_hp/do_not_adjust_final_state true

This makes the phenomenon I mentioned earlier resolved.(I want to simulate the process “nCapture” and record the following effects.)
But there are still existing the fact that the sum of gamma rays plus than 7.6MeV（from Fe56 capture neutron).

I wanna know what’s gonna be different if I add this:

/process/had/particle_hp/do_not_adjust_final_state true

[mkelsey]

Not sure. I think that final state adjust is supposed to rebalance things, possibly even adding or deleting secondaries, to get energy conservation. Since PhotonEvaporation does that anyway, I think you might not want that setting.

[dengmanna]

@mkelsey

不确定。我认为最终状态调整应该重新平衡事物，甚至可能添加或删除辅助节点，以实现能源节约。既然无论如何都这样做，我认为您可能不需要该设置。

Is that being “false” as default? Or I should define it as “false” in my simulation?

[mkelsey]

Try removing it (or setting the flag to false), and see what happens.

[dengmanna]

Thank you!
I found that if i remove it, things as I proposed before would happen.