The US Federal Code of Regulations has a section defining acceptable radiation doses for radiation workers[1]. This section places an upper limit on the shallow

The US Federal Code of Regulations has a section defining acceptable radiation doses for radiation workers[1]. This section places an upper limit on the shallow dose to the skin of 50 rems. To get an equivalent shallow skin dose from a backscatter machine, you would need to go through it over five and a half million times. The limits for adult members of the public are 10% of the limits for radiation workers, which would cut it down to only about 500,000 times through. To be fair, I haven't found any studies either way on the safety or danger of the 10 C.F.R. 20 limits, probably because very few people get close to hitting the dose limits. One study I found[2] that surveyed radiation workers in three different studies concluded that the relative risk for a sustained protracted dose of 10 Rems compared to no dose is 0.99 for cancer excluding leukemia, and 1.22 for leukemias. This means, as a radiation worker, you're somewhat less likely to get a non-leukemia cancer, and about 20% more likely to get leukemia. This is for a dose that is over a million times larger than what a backscatter machine will give you. Furthermore, these risk rates are lower than what would be expected from a linear estimate based on cancer rates in atomic bomb survivors, suggesting that smaller radiation doses are safer than larger ones, and the dose these machines give you is about 200-500 times smaller than the does you're going to get on the airplane (if you're flying cross-country). I just wanted to put in perspective that the dosage these machines put out is extremely small when compared to the dosages you might normally receive, let alone the dosage which radiation workers commonly receive. Their health effects are minimal, and if they actually contributed to the safety of passengers, I'd say they'd absolutely be worth it. The real travesty here is that they violate privacy for no real gain, not that they are in any way a significant health risk. [1]: http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/ http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/ [2]: http://www.jstor.org/pss/3579020 http://www.jstor.org/pss/3579020 (JSTOR link. If you're not affiliated with an academic institution, you'll only be able to read the first page)