[ggoss]

It also depends on whether the machine in use (different airports use different machines) are millimeter wave or backscatter x-ray. Millimeter wave machines (the majority of installations), if I am not mistaken, do not emit ionizing radiation, whereas the backscatter machines do. You can tell which type of machines are in use at your airport by the informational posters displayed in the queue, the brand and physical appearance of the machines themselves, or by checking online. My policy has always been to ask for a pat-down when they use backscatter (to avoid the unnecessary radiation), and go through the machine if they use millimeter wave. The dose of radiation may be small (relative to normal amounts of cosmic radiation or black lightning or bananas or ...), but they don't really know if the machines are out-of-spec until, well, they do. I'd like to avoid becoming 'that person' who was severely over-radiated right before they decommissioned a malfunctioning machine.