I’m studying the decay of Ra223 within a world with micrometric dimensions. This isotope decay to Rn219, and the latter to Po215.
The problem is that I’m observing too few Rn219 decays and no Po215 decay. I have realized that the mean free path (MFP) after the decay depends on the initial daughter kinetic energy and half live time. This leads to MPF much longer than the dimensions of the World so Po215 nuclei escape from it “always”.
Supposing I’m right on this, how can I force the decay to occur immediately?
I’ve tried to solve this issue by setting a very long /grdm/hlThreshold but it did not work.
Thanks in advance.
I guess the question is are your dimensions a realistic reflection of the device you’re modelling? If the recoil daughters are escaping, then they would do that in real life, right?
You are right but I wanna reproduce a sort of particle equilibrium.
My main concern is that daughters should not travel distances defined by their velocity and life time within a condense medium like water. This should be determined by the mean free path according to their macroscopic interaction cross sections. Or am I wrong on my interpretation of the transport algorithm?
You’re correct. And in fact, that’s how it works. The recoil daughter is treated as a secondary, and it travels according to the usual interactions. Generally speaking, nuclei in dense media are only going to travel microns, maybe mm at most, before stopping and decaying.
That said, because they’re so heavy, the regular Geant4 physics lists will generally have nuclei stop in one step, losing all of their energy. In TestEm8, the G4ScreenedNuclearRecoil process (and related stuff) treats this with smaller steps.
example radioactivedecay/rdecay01 : lines 120-124 of TrackingAction.cc