Keith, I had a long discussion with a senior security operative at London, Gatwick last year. He sits on a committee with Ilford, Kodak & Fuji specialist about film safety & airport scanners. Modern hand baggage scanners are totally safe for multiple passes for virtually all films.
The data from the scientific studies by this organizaiton that Ian refers to can be found on the internet. The industry association is called I3A. Links to the reports have been posted on APUG (several times in the past) and LargeFormatForum.