Beta interactions

Beta particles are electrons. As shown in the following plot taken from the review article Passage of Particles Through Matter in PDG, electrons lose their energies in matter primarily through ionizing atoms around them (Geant4 name: eIoni) below 10 MeV. More energetic electrons are more likely to generate photons through Bremsstrahlung (Geant4 name: eBrem). Multiple scattering with orbiting electrons (Geant4 name: msc) is a subdominant way for an electron to lose energy.