Too many gamma-rays from neutron capture by nickel-58?

Dear all,

Now we are checking the energy of gamma-rays generated from neutron capture of nickel using Geant4.10.03.p02.
I defined the material using Nistmanager

G4Element* elNi = NistManager->FindOrBuildElement(“Ni”);

and the information of all steps is saved.
When I checked each step, I confirmed that 3 gamma-rays of ~9 MeV were generated from 1 neutron capture by nickel-58.
If my understanding is correct, total energy of gamma-rays generated from 1 neutron capture by nickel-58 is ~9 MeV.

Is my understanding is correct?
And has anyone ever done a similar analysis?
I would appreciate it if anyone give me any comments.

Best regards,

The Q-value for 58Ni(n,gamma) is ~8.998 MeV. So if an 8.998 MeV gamma is emitted in an event it must be the only gamma. Likewise if an 8.998 MeV gamma is emitted in a single capture event, there cannot be a 8.533 keV or a 0.464 keV gamma at the same time. They are part of a 8.533 -->0.464 keV cascade so if the cascade happens, the Q-value-to-ground-state transition cannot.

I am not exactly sure of what you are outputting. Two of the three 8.998 MeV gammas are from Transportation processes and one from a conversion process which could suggest that the three gammas are really same gamma. However there are also two 8.533 gammas and one 0.464 gamma. The cascade shouldn’t appear with the 8.998 if only a single neutron capture has occurred. That suggests that you are seeing results from multiple neutron captures in your output.

Here a macro for example Hadr03 (in extended/hadronic), its printout and the gamma spectrum plot.
From them we can say : there is on average 4.067 gamma per event from neutron capture, with mean energy of 2.1 MeV. A total of ~8.5 MeV per event, which confirm your analysis.

sakai.mac.txt (344 Bytes)
sakai.out.txt (2.5 KB)

I’m so sorry for being late for ~4 months to reply…

Thank you so much for replying.
The explanation of the output was not enough…
Each column means below.

Inc.fParent : Track number of the parent particle
Inc.fTrack : Track number of the particle
Inc.fStepI : Step number of the particle
Inc.fCreat : Process name by which the particle was generated
Inc.fParti : Name of the particle
Inc.fProce : Process name that the particle occurs at each step
Inc.fpreEnergy : Kinetic energy of the particle at pre-step
Inc.fGTime : Global time from generating the primary particle

It seems that these 9 gamma-rays were generated by single neutron capture at the same time.
And now I’m wondering if this is caused by our fault or Geant4 bug…
This was confirmed even in the Geant4 version 10.05.p01.

I’m so sorry not to reply for a long time…

Thank you so much for checking the energy of each gamma-ray generated by neutron capture of Ni.
As far as I checked your histogram, there seems to be no problem about the energy and the number of gamma-rays…

I checked total energy of gamma-rays from neutron capture.
I generated 100,000 single neutron from the center of Ni-Cf source (mainly made from NiO pellet, Araldite and Brass rod).
The energy of each neutron is shown below.
And I confirmed total energy of gamma-rays from primary neutron capture by each nucleus.
In the following histogram, green line shows that by Ni nucleus, and we can confirm that total energy of gamma-rays is higher than Q-value for Ni nucleus.
I’m not sure the reason why…

n_energy.pdf (15.0 KB)
Total_gamma_energy_from_n_capture_Logy.pdf (26.7 KB)

Here I attach the schematic view of the simulation for checking total energy of gamma-rays.
The radius of Ni-Cf source is 8 cm.

Ni-Cf.pdf (30.1 KB)

I do not know the nature of the Ni-Cf source, but if the Ni and Cf are interspersed and distributed, is it possible that you are seeing a few gammas from some fast neutron capture or other fast neutron reactions? I ask because in your first table above from Aug 31, the 0.9346 MeV gamma ray does not correspond to thermal neutron capture by 58Ni or indeed any of the other isotopes of Ni that I can find (the other gammas are all from thermal neutron capture on 58Ni).

Thank you so much for your advice.
I’m not sure why 0.9346 MeV gamma-ray was generated, but all gamma-rays in the first table should have been generated from a single neutron capture of 58Ni.

In fact, this problem has recently been solved.
According to an expert of our research group, total energy of gamma-rays from a single neutron capture seems not to be conserved in default setting.
And this problem was resolved by setting the environment variable “G4NEUTRONHP_USE_ONLY_PHOTONEVAPORATION” before running Geant4.

Setting G4NEUTRONHP_USE_ONLY_PHOTONEVAPORATION may solve the energy nonconservation problem, but as I described in the post , the gamma spectrum is generally better (that is, closer in energies and relative intensities to NNDC data) if G4NEUTRONHP_USE_ONLY_PHOTONEVAPORATION is NOT set (=0). This is true in particular for 58Ni. Setting the flag to 0 does have some weird side effects, however.

Thank you so much for your information.
I’ll check the topic “Thermal neutron capture gamma spectra give major disagreement with NNDC data base for some isotopes” later.