Hi all. Absolute newbie here. New to both GEANT4 and C++, though I have significant experience with MCNP.
I’m attempting to create a simulation of a neutron source placed near a thick-walled 3He gas neutron detector. I’d like to tally number of neutrons absorbed (per source particle), as well energy deposited in the gas by proton and triton secondaries after neutron absorption in 3He.
I started with example B1, and modified DetectorConstruction to introduce my materials and build my geometry. I’ve confirmed the geometry using Qt. I’ve looked through some examples in \hadronic\ (for neutron source definition) and \radioactivedecay\ (for pulse height tallies). I’m not sure how to modify the codes to include n + 3He → 4He → p + 3H processes, or if these are already included. I would appreciate any guidance on how to include these effects and tallies.
Frankly, I’m a bit overwhelmed by the number of GEANT4 functions and files (I know it’s not much, but coming from MCNP anything larger than 1 file seems like a lot), and it’s unclear to me how it all fits together.
Many thanks for your help.
Geant4 Version: 11.2.2 Operating System: Windows 11 Compiler/Version: VS 17.10.2 CMake Version: 3.30.0
You are going in the right direction. Before spending more time in learning by trial and error, I would advise to follow the basic course of Geant4 [1] given early this year, particularly the sessions that were recorded and the slides.
There are 3 main pillars to run a simulation and get the information out:
Geometry, which you have already implemented,
Physics, one can use the built-in physics lists [2]. These physics lists (FTFP_BERT, QGSP_BIC, and their variations, eg FTFP_BERT_HP, FTFP_BERT_HPT) can simulate the neutron capture in 3He.
Actions. During the beginners course, they show how to extract information inside the “step action”. As you said, here it is where you have to write the code to record the energy deposited in the gas.
By doing this, you should be able to see the 764 keV peak and the tail at lower energies caused by the wall effect.
I guess that your 3He detector can work in ionization/proportional mode, in any case you can assume as a starting point that the output electrical signal is proportional to the energy deposited in the gas.
I guess that to simulate the moving charges in the gas one shall resort on dedicated software such as Garfield.
I hope this helps a bit. Maybe other experts can give more insights.
Thank you for the resources. My student and I will take a look.
I have simulated this geometry using MCNP, and I’m trying to do a benchmarking comparison against GEANT4. MCNP doesn’t apply any acceleration due to electric field, so I wasn’t going to do that in the GEANT4 code either.
Thank to you for taking the time of using Geant4. I would appreciate if you could come back and show how different are the results from MCNP and Geant4. I think it can be useful to motivate future developments.