So, high energy electrons must be from near source (mostly, inside our galaxy), because otherwise they will slow down by magnetic field of our galaxy.
For high energy protons, this eased, but I could not remember approximations for possible distance.
And for heavy nucleus, may be possible to travel from very distant source, even from borders of Universe.
Latest accelerators are not very suited for such activity, but earlier linear accelerators works well on this, and give very interesting data.
So, high energy electrons must be from near source (mostly, inside our galaxy), because otherwise they will slow down by magnetic field of our galaxy.
For high energy protons, this eased, but I could not remember approximations for possible distance.
And for heavy nucleus, may be possible to travel from very distant source, even from borders of Universe.