Back in high school, in the mid 1960s, I remember a thick blue book of
science fair projects, I believe from Scientific American. It included a
Van de Graaf machine to generate high voltage, and an electron
accelerator to stand next to it. It included construction details. The
vacuum pump came from an old refrigerator, and the electron source was
the filament from a vacuum tube (easy to find back then, not so easy
today). They did not discuss at all what to do with it....
Today I am a particle physicist with experience designing accelerators.
I now realize that this is not at all an easy project (e.g. an old
refrigerator pump is unlikely to give a good vacuum). I also know that
to build one today would require a license from the Nuclear Regulatory
Commission, which an individual is unlikely to obtain.