Why is there difference between simulation results and theory in gamma-ray distribution from the deexcitation of Cd-114

Continuing the discussion from Can't see 558 keV peak from the deexcitation of Cd-114:

I’m simulating the interaction between Cd-113 and 0.0253eV thermal neutron. The gamma-rays from the deexcitation of Cd-114 can be seen clearly after setting USE_ONLY_PHOTON_EVAPORATION, but the distribution of their kinetic energy is quite different from the theoretical one:

My simulation result:

The theoretical one:
seen in Thermal Neutron Capture Gammas - Target 113Cd

It’s very unnormal that the number of 745 keV gamma-rays is greater than the one of 558 keV. What should I do to get a right result? Can I change the data set about the distribution in Geant4? I will appreciate for your help.

I was having trouble matching experimental thermal neutron capture gamma ray intensity ratios to Geant4 simulation values for some nuclei other than Cd113. I finally settled on the following NeutronHP parameter values that reproduced the ratios reasonably well for that limited set of nuclei:
UseOnlyPhotoEvaporation 0
SkipMissingIsotopes 0
NeglectDoppler 0
DoNotAdjustFinalState 1

I have only tested Li6, Li7, N14 and Ni58 so far but I’ll be doing more isotopes. In the meantime, you might want to try the settings for Cd113 and let me know if it helps.

Note that it’s important to make sure the parameter values are set correctly by looking at the terminal output. I originally was setting them as environment parameters in my .bashrc file. They were somehow getting modified when I ran the program. I now set them explicitly in the code. I am running Geant4 10.7.2.

Thank you for your advice, I tried the commands you list but they didn’t lead to a better result. If I set UseOnlyPhotoEvaporation as 0, the energy of gamma-rays generated from Cd-114 will be continuous, instead of a few certain values. What’s more, the other commands hardly influence the gamma ray intensity ratio, whether their value is 1 or 0.

That’s interesting, because I got almost the opposite result. Gamma ray intensity ratios were all wrong with UseOnlyPhotoEvaporation set to 1 and were correct with it set to 0. The other parameters had little effect. With UseOnlyPhotoEvaporation either 0 or 1, the gamma rays were discrete lines with no or a very small continuum.

I tried C-12 and the result from UseOnlyPhotoEvaporation=1 is still better, but this time I didn’t see any continuous distribution of the gamma-ray energy whether UseOnlyPhotoEvaporation was 1 or 0. Can you tell me where you find the theoratical statistics to compare with sumulation results? I think the references we use might be different.

I am not using theoretical statistics. I am comparing my simulation with neutron capture gamma ray intensities from the National Nuclear Data Center at Thermal Neutron Capture Gamma-Rays (CapGam) . They use data from ENSDF and XUNDL data bases maintained by NNDC (Brookhaven National Lab). I have now also done B10, G4_Be, G4_C and G4_Al with moderate to good agreement.

Thank you for the information you shared. We are using the same data source. I wrongly judged it to be theoretical. I think I have to do more simulations to determine which configuration is better.

I am starting to realize that I also do not know the best configuration to use. The configuration I mentioned above (notably UseOnlyPhotoEvaporation = true) worked well with light nuclei (Li6, Li7, Be, B10, Li, C, N14, Al), but agreement with NNDC data were mediocre for Ni58 and poor for Ni60 and Gd155.

With UseOnlyPhotoEvaporation = false, I get good agreement for C, N14, Ni60, but mediocre results for Be, B10, Al, 155Gd and poor results for Li6, Li7, Ni58.

At this stage, I essentially have to vary the parameters for each nuclei that I want to use to determine the best set. I do not yet have a systematic method of selection. If anyone out there has any suggestions, they would be appreciated.

Hi, if you have a better experimental cross section, you may change the G4NDL database file, at your own risk. I am preparing a guide of the format of these database files, write me and I can give you a first version of it (pedro.arce@ciemat.es)