I really like that video. However, I think this could have been done with X-rays by adding heavy salts (ex. sodium metatungstate or vastly more hazardous thalli

I really like that video. However, I think this could have been done with X-rays by adding heavy salts (ex. sodium metatungstate or vastly more hazardous thallium salts) to the water or using a heavy organic liquid (ex. diiodomethane). However, if you have a neutron imaging beamline you probably are motivated to make a cool demo.