Earlier quoted context omitted.
The scanners we have in the US are using radiation. Some of the scanners used in Europe are using sound waves instead. (I noticed this because I always opt out of the radiation ones.)
I'd recommend not travelling through Manchester Airport then, which have backscatter machines in place and do not allow for opt-out (although this is as-per DfT guidelines). They do only test a random sample, however. The Department for Transport has full confidence in the independent assessment undertaken by the Health Protection Agency. We are confident with their assessment that the dose from being scanned is far…
My chief concern is that the security agencies have often been known to lie and/or be technically incompetent when it comes to such things. Case in point: I still remember when we were being told that going through the xray machine doesn't damage film. It does, but it took them YEARS to admit it. So now we're being told that this machine (when being operated correctly and when working properly and when it has been properly calibrated) merely poses "acceptable" risks to health. We know the people running the machines are largely idiots and we have reason to suspect the machines aren't entirely idiot-proof - because almost nothing is. Frankly, I wouldn't trust the TSA to operate a blender safely; they're the last people I want giving me an x-ray scan.