Both and more. The danger from the beam is limited to a specific energy intensity, otherwise the beam will pass through without depositing much energy (there is

Both and more. The danger from the beam is limited to a specific energy intensity, otherwise the beam will pass through without depositing much energy (there is ways to calculate this). The bigger dangers are all the atoms the beam knocks out on it's way that are likely to transmute into radioactive isotopes via various modes of actions as well as the hard bremsstrahlung generated by the beams interactions as well as some of the stuff it knocks along (there is enough energy that if the beam knocks into an electron, the electron will dump some bremsstrahlung while it slows down again).