How to track a positron below 100 eV?

Recently I’m trying to track the positrons using the standard EM physics. However, it is strange for me to find that the 100-eV positrons travelling in a Laboratory vaccum would lose all their energy because of processes named “Transportation” and “eIoni” within a single step. This seems to be related to the low energy cut of the G4eIonization process, but I currently have no idea how to change it.
Moreover, I’m interested in tracking positrons with energy below 0.025 eV, is it feasible using the EM physics, e.g. Penelope, livermore? Or does it need a more specifically designed EM physics?


by default it is not expected that e± are tracked in details below some threshold. Depending on Physics List it is 10 eV - 1 keV. If you want to track low energy positrons, the first thing is to remove tracking cut:

/process/em/lowestElectronEnergy 0.0 eV

You also may need to change tracking parameters

/process/eLoss/StepFunction 0.1 0.001 mm

The last proposal is not mandatory but may be needed.
Finally the most important thing: you need to know how electrons are distributed in your geometry. Is there electron cloud? What is the value of surface potential? Positrons may annihilate in different way depending on answers on these questions.