I would like to as if Geant4-DNA permits the radiation transport of positrons at low energies as it is made for electrons. I am using some positron sources am I found significant differences between the energy deposit at the macroscopic level (cm) using EMOpt4 and the microscopic level (um) using DNAOpt0 (with activator), DNAOpt2, DNAOpt4, and DNAOpt6.
I looked into DNAOpt0, DNAOpt2, DNAOpt4, and DNAOpt6 files, and I found that the positrons are transported as in EMOpt3, and the annihilation process is not considered.
If the positrons are out of the Geant4-DNA physics processes (low energy), is there a possibility to use DNAOpt0 + Activator (EMOpt4) until 10 eV for positrons? What could be the cons in that case?
There are no Geant4-DNA physics processes for positrons. However, I think you may use EMOpt4 down to 10 eV. Now the question is: how accurate are the models? we do not know below few hundreds of eV. As you probably know, there is research aimed to understand more in depth the interactions of positrons at low energies in the biological medium.
Thank you very much for your answer. I am happy to have a reply!
I searched for some publications to see how to handle the positron on Geant4-DNA, but I realized there is not much information. I found a publication from Chatzipapas et al. (IDDRRA tool to quantify DNA damage). Still, there, it is not fully clear what they did: “The significant differences observed between positrons and electrons are due to the different physics list used, since the Geant4-DNA discrete physics models (G4EmDNAPhysics_option4) do not handle positrons and we were obliged to use a condensed-history model (G4EmStandardPhysics)”.
I was planning on a first try to implement the positron processes of EMOpt4 into the DNAOpt2. Another approach is to make some changes to the G4EmDNAPhysicsActivator class. Do you think it could be a good way?
what I mean is that there is research to understand better the interactions of low energy positrons in matter. In other words, it is not just a problem of software implementation. In your case I would suggest to use the Livermore physics list and push the low energy limit to 10 eV, that is possible by a software point of view. Still, I would like to mention to treat with care the results deriving from the simulation because we do not know know the uncertainty affecting the results. Still I think this is the best option if you are interested to study low energy positrons.
Thank you very much for the clarification. I think I will keep the positron sources outside of my study and wait for new developments in the Geant4-DNA physics lists. I did some tests, but the results are inconsistent, and the error increases with the energy of the emitted positrons (F-18 < I-124 < Ga-68) (probably because of the applicable energy ranges).
Thank you for this opportunity. I will prepare a description of my simulation with the code I changed into the DNAopt classes and results. I am a beginner on Geant4, so that I could be doing something wrong.