Morten, no, I donīt think there are rules for xray machines at home because there is not much reason to have one at home at all. ;-)

I know a guy who has a small x-ray source for photographic usage - but he is from that business, installing and servicing them and got that one from a dentist who got a new one.

Most modern systems (besides those digitals) donīt fog the film by themselves - the sources are small, radiation is relatively minute. IIRC they expose a luminous film which then only fogs the film itself.