I am building a simulation (Geant4 v11.1.0) based off of the rdecay01 example, where I am calibrating a Germanium detector. When I use Sodium-22 as the particle source, I expect to get a large peak at 511 keV, corresponding to the Electron-Positron Annihilation from the Positron produced from the beta decay. Instead, I get a dip at that location, seen here at the first black dashed line:
I have tried changing physics lists and returning to older versions of Geant4, and I either get the same result or no data whatsoever. I have also tried switching the material from Ge to NaI, but that still gives me a similar result.
Would someone be willing to take a look at my simulation? I currently have no idea where to approach this problem from here.
I’m sorry no one has addressed this yet. I’m a newbie as to code, but here’s a question: do you have any passive material in the simulation around the detector? If not, and your simulation is just a bare detector, then the positrons are annihilating in the detector and there is kinetic energy deposited when they slow down as well – so you will get a continuum above 511 keV but not a narrow line. This is probably your bump that peaks around 0.65 MeV. I see (I think) the escape peak at 1.275 minus 0.511 keV, which you get when positrons annihilate inside your detector and one of the gammas escapes. So this seems to me to be a successful simulation of what I would expect to see if you have no passive material around. You could try putting a slab of anything underneath the detector and see if the annihilation line pops up then, as it should when positrons annihilate in your passive material.
