Neutrons can be used for these things as well. The advantage, say from x-rays, is attenuation is not by material density, where all metals will just look dark, but by thermal neutron absorption cross section. So boron might be dark, but metals won't be.

Muons are much nicer as you don't have to carry a neutron source around with you.

> However, if anyone is now thinking of standing under the bridge to get their body scanned, they shouldn't bother. First, they'd have to stand still for an hour, and second, the security patrol would be there within minutes.

Security patrol will come and bother you if you hand around the bridge for a few minutes?