Hi John,
I used Geant4 10.07.p03 with G4NDL4.6 to simulate Gd’s thermal neutron(0.025eV) capture gamma energy spectrum. I set the parameters you mentioned above, but I still got some extra peaks compared with the IAEA database. After you upgrade the version of geant4, have you simulated the capture gamma of Gd155 or Gd 157？
Best wishes
Hi,
No, I haven’t tried either Gd155 or 157 since upgrading to Geant4 11.0. I will try them, however, and get back to you.
I did a couple of quick runs using Hadr03 with Geant4 11.0.2. I am using the QGSP_BIC_HP physics list. For Gd155:
and for Gd157 (which I think is what you are showing in your post):
The Gd157 result is similar, but not identical to yours (but then I do not know exactly what your geometry, scoring, etc. is). The different physics list should not matter for 25 meV neutrons. Without doing a detailed analysis, it seems in both cases as though many spectral lines match in energy the NNDC data base, but the intensities are not even close.
Hi John,
Thank you very much for your time! The element in my simulation is G4_Gd, so my energy spectrum contains contributions from Gd155 and Gd157. And the figure with the title “database” also contains contributions from Gd155 and Gd157. So I think the results simulated with Geant4 11.0 are similar to what I got with 10.07.
As you said before, the gamma intensity is not the same as the database. In order to get the same intensity, can I modify the intensity of the gamma ray in the step action? For example for 3700keV, the cross-section is actually only 99b, I will kill secondary gamma rays with the energy of 3700keV in step action with a certain probability to reduce the equivalent gamma intensity. I don’t know if this is helpful.
That might solve your specific problem, but it would be onerous to generalize it. Such conditionals in the user Stepping Action would be required for each specific problematic material (with possibly many energies per material). Although I am not sure, I imagine that the additional stepping actions would slow things down too.
It would be better if the neutron capture processes and data bases were modified to better reflected reality.
Hi @John_McFee, I am quite new to Geant4 and am very much a beginner - I was wondering how you edited the Hadr03 example and corresponding macro(s) to obtain the Gd157 spectrum? I am just trying to simulate a basic gadolinium spectrum and was wondering if you could help?
I am using version 11.0.0 of Geant and ROOT 6.26/06, and the examples do run successfully on my machine. Thank you! 
Hi @avmc1,
I used the QGSP_BIC_HP physics list instead of the default. So in PhysicsList.cc, you have to comment out line:
RegisterPhysics( new G4HadronInelasticQBBC(verb));
and uncomment line:
RegisterPhysics( new G4HadronPhysicsQGSP_BIC_HP(verb));
then recompile.
Here is the macro I used for thermal neutron capture on Gd157:
Gd157_nCapture.mac.txt (1.6 KB)
The README file in the distribution example explains how to run Hadr03 with a macro (.mac) file.
Hope it helps.
Hi @John_McFee,
This is a great help, thank you so much! All is running perfectly.
Forgive my ignorance, but I was wondering how you have made your gamma spectra above look like a spectrum. My histogram for kinetic energy of gamma rays just outputs individual points (below) - is there a way to draw this so it looks like a spectrum like yours do? This is probably a very basic question so sorry for that.
Thank you,
Abbie
Hi ,
I uncomment the two lines in the .mac file (not needed if you are using the unmodified version of Hadr03.cc from the distribution):
/process/had/particle_hp/use_photo_evaporation true
/process/had/particle_hp/do_not_adjust_final_state true
I output a .ascii file with same name as the .root file (that’s what the /analysis/h1/setAscii 2 line in the macro does). I then use a separate Octave program (it should be able run under Matlab too) to plot the spectrum. I’ve attached that program as Read_Hadr03Ascii_Spectum_Plot.m.txt. To use it, remove the .txt extension, move it to the same directory as the .ascii file, gzip the .ascii file, change the path to the ascii input file in the .m program to match where it is on your computer. Then run the program under Octave.
Read_Hadr03Ascii_Spectum_Plot.m.txt (2.9 KB)
Of course, you can use any external software you wish instead.
Good luck.
John
you could also try linear scaling of the y-axis instead of log, because then the bars of the histogram can start from 0.
@John_McFee can you please post your result for Argon. I’m obtaining big discrepancies as reported here : Discrepancy on gammas from thermal n capture on liquid argon
thanks!
Hi Luis,
I have a LibreOffice spreadsheet for 35Cl(n,gamma), 36Ar(n,gamma), 40Ar(n,gamma), 58Ni(n,gamma) comparing Geant4 simulation energy and intensity results to the NNDC data base. However, this forum does not support .ods files for uploading. Please let me know your email address and I will send it to you.
Hi @John_McFee John, you can use manzanilla+lapp_in2p3_fr, with “+”->“@” and “_” → “.”
Could you please include the exact settings for your simulation?
Thanks in advance!
I have sent you the spreadsheet and exact settings used to get the results.
Dear @John_McFee , I am also facing the same problems with neutron capture in liquid argon that have commented in previous posts. Would you mind to share with me your results in argon and the settings you’d recommend to use in order to get a good simulation of this process?
Thank you very much in advance
Sure. Just send me your email address.
It seems the way Geant4 is using the NNDC database will produce in all scenarios gammas that are not supposed to be produced. The best you can do is place this in your mac file:
/process/had/particle_hp/use_photo_evaporation true
/process/had/particle_hp/do_not_adjust_final_state false
/process/had/particle_hp/skip_missing_isotopes true
but the results will still be far from measured data. The solution that I implemented is creating my own generator of gammas from neutron capture on Argon. Another solution could be just edit the files that Geant4 will use but these files are used in other processes as well so I’m not sure is that is a good idea.
You can find the implementation I did here for Ar40 and Ar36:
Then I just call an faction in my primary generator action. With this I get a fair agreement with data
Hi @lmanzanillas , this is really useful. Thank you very much for sharing this information. I’ll keep working on the simulation and I’ll post any significant finding.
best,
Miguel
