I ask this simply because anti-X activists have pushed junk science claims of the form "X causes CANCER" many times , so I'm a little dubious. I don't think fighting civil liberties violations with junk science is a useful tactic, if that is indeed what is happening here.
 For example, feminists pushed the "silicone gel implants cause breast cancer", anti-bioscience types push "GMO foods cause cancer". Drug warriors have pushed "pot causes cancer" and anti-abortion crusaders pushed "abortion causes cancer".
Ordinarily I'd (enthusiastically) go along with the standard that this implies: until proven otherwise, you ought to be able to do what you want with your body (and maybe even after it's proven unhealthy).
This situation is different. Because the crucial element of personal choice has been removed, the burden of proof must shift 180 degrees. It is incumbent on those forcing the test on us to prove beyond any reasonable doubt that there's no danger involved. And when there may be dangers (as with the woman in the OP who had been told to avoid X-rays), it's also responsibility of the authorities to provide work-arounds.
EDIT: fixed "healthy" in 1st para to "unhealthy" -- oops.
The majority of their energy is delivered to the skin and the underlying tissue.Thus, while the dose would be safe if it were distributed throughout the volume of the entire body, the dose to the skin may be dangerously high.
This statement is very shady. When a photon interacts with a cell, it has a certain (small) probability of causing a carcinogenic mutation. The probability that the radiation is safe is (1-P)^N, where N is the number of interactions . The fact that it is all deposited in the skin is irrelevant to leading order , this simply makes skin cancer more likely than breast or liver cancer.
I.e., if the dose in the form of a chest x-ray caused a 1e-9 chance of skin cancer and 1e-9 chance of breast cancer, it instead causes a 2e-9 chance of skin cancer with comparably reduced breast cancer risk.
 I'm ignoring high field (nonlinear) effects, since if the field were strong enough to cause them, it would probably also vaporize the person being scanned.
 It's actually a good thing since many skin cells are dead or will soon die, and thus carcinogenic mutations will harm them less.
I'm also no expert, but surely there is a risk of more significant, irreparable genetic damage accumulating if several photons interact with the same skin cell, as opposed to those same photons interacting with several different cells throughout the body?
Well they are, so perhaps we should give their word a bit more credibility than yours?
But I guess it's much easier to criticize me for being a mathematical physicist rather than a medical doctor. After all, finding flaws in an argument takes work!
Well, X-rays cause cancer. BS uses X-rays So it is a cancer risk.
And it is a little more founded than someone randomly saying' this causes cancer'.
In terms of risk...
This says dental x-rays are about 2-3 mrem:
This says BS is about .006-.009 mrem:
Keep in mind that under certain models (the 'no-threshold model'), any amount of exposure (even a tiny amount) to an X-ray is a slight increase in the chance that that person will get cancer.
Now you might think that because dental x-rays are about 300 times more powerful than BS, dental x-rays have a much higher chance to cause cancer. Sure, individually, my chances of getting cancer from a BS are much lower than my chances of getting cancer from a dental x-ray. It is even higher from daily background radiation, or from the radiation that you get from flying in an airplane.
But everything is about context. How many people fly each day? 2 million or so? How many people do we propose to put through the BS machine? All of them? (I assume the intent is to eventually replace the metal detectors with these). If you are putting 2 million people through the BS each day, that is actually large amount of radiation exposure. Probabilistically, someone will get cancer from the BS.
There are certain types of radiation that you can avoid (x-raying your foot for fun! backscatter machines), and there are certain types of radiation that you cannot avoid (background cosmic).
I don't see how the argument that it is 'nothing' in comparison to other forms of radiation really stands up, in that I could potentially avoid backscatter radiation, whereas I couldn't conceivably avoid the other types.
(This doesn't take into account other real issues, like 'what if the machine breaks down and we start blasting people with focused beams of radiation'... while trained to run the machine, I doubt that the TSA people are trained to maintain the machine, or would even know if something had gone horribly wrong with it).
What if my flashlight breaks down and I start blasting people with focused beams of laser light? What if my cell phone breaks down and the microwaves melt the brains of everyone within 6 feet of me?
I don't know a great deal about the engineering of MWBS, but I see no reason to believe that your fear is any more likely than mine. Most machines just don't work that way. Do you have evidence that MWBS is different?
With a backscatter x-ray system, the person stays motionless and the x-ray source moves. If the x-ray source stops moving, the person receives an excessive dose wherever the source happens to be pointing when it gets stuck. The dose received is, again, a function of how long it takes for the operator to notice the malfunction.
With a microwave backscatter system, the radiation used is in the RF range and, therefore, not ionizing. However, if the microwave source stops moving because of malfunction, a portion of the body experiences higher than normal SAR. If the SAR is high enough, significant localized heating may occur, causing burns on the person.
As long as the backscatter machine doesn't run on Double A's, my fears are actually more reasonable than yours.
The backscatter machine presumably uses some sort of electrical plug to connect to power. It isn't inconceivable that it could receive more power than intended and produce more x-rays, or that something could go wrong with the shielding allowing x-rays to leak, or that something could go wrong with the x-ray bulb and we could produce the wrong type of radiation.
And it doesn't have to be 'burning your head off' to be a problem, it could simple produce an order of magnitude or two more radiation than intended, and be a health risk.
Look, I'm not saying your fear is physically impossible. I'm just saying I can't think of a very many machines (radiation sources or otherwise) for which anything similar is a plausible fear. Most machines simply stop working when used outside their operating parameters.
Also, do you really think that if the backscattering machine emitted the wrong type of radiation (x-rays of a different frequency), the TSA agent operating the scanner wouldn't notice when his screen went blank (unless the detectors simultaneously malfunctioned to pick up the incorrect frequency)?
Your desk lamp doesn't emit X-Rays, you don't force droves of people to stand underneath it, and no oncologists ever told me to be wary of your desk lamp until it has received further study.
So, yeah. Not the same thing. Not even remotely. In fact, your analogy is a bit silly.
Medical radiation machines deliver 45-80 Gy. The backscattered x-ray machine delivers 1e-7 Gy, if I've got my math right. That's roughly the difference between a punch and a nuclear bomb.
The fact that a cell killing radiation cannon malfunctioned and killed someone does not imply that an illumination device billions of times weaker could do the same thing. Similarly, a laser scalpel will kill you if you shine it on the wrong place. A flashlight won't.
The burden of proof of safety lies with the TSA and scanner manufacturers.
Are the scanners designed or even capable of doing the same?
What evidence do you have that it is actually not possible for the machines to dangerously malfunction, and how much confidence can actually be placed in it? Those telling us it is safe don't have entirely clean hands on the topic, they've lied about other things like picture retention policies and capabilities before.
You're making an appeal to incredulity. I would not actually be that incredulous to discover that the machines do indeed have some sort of flaw that would permit them to blast out more radiation than intended. After all, it's happened before. That said, I don't necessarily consider it likely, either, what I find far more problematic is that this is merely one consistent piece in a larger puzzle of unconcern about the real safety of the public.
For the same reasons we ought to be able to examine our voting machines, we ought to be able to examine these machines.
A smaller radiation source, like that of an x-ray backscattering scanner, does not need to have a "deadly radiation" mode. And it's highly unlikely that a hardware failure can accidentally turn "10x weaker than chest x-ray" mode into "deadly radiation mode". The more likely failure mode will be something along the lines of "6x weaker than chest x-ray mode".
It's just highly unlikely that any device will accidentally emit millions to billions of times more energy than it was designed to.
Again, not really worried about this, I'm more concerned by the blithe acceptance of the idea that nothing can possible go wrong.
(Yes, this is quibbling about what was probably just an error in definition; I think your comments are right as applied to backscatter X-ray scanners. But if we keep our language straight, our arguments against these blasted things will be that much harder to dismiss.)
The concerns raised in the UCSF letter are strained beyond belief. Further, a number of points (like the breast-cancer bullet point) are clearly there to influence emotions rather than critical reasoning.
I'll just explain this one. As the UCSF letter states, the radiation is being deposited on a volume smaller than usual by a factor possibly as large as "one to two orders of magnitude". That means that at absolute worst this is like radiation dose of 1 mrem (still less than the flight tiny compared to your yearly dose), and that's assuming that all of the risk of cosmic radiation comes from skin cancer (which is wildly wrong).
there are so many issues swirling around this subject- privacy, security, safety, fear, "terror"... i guess i'm just wanting the science of the safety to be completely objective, open, reviewed, failsafes and failure modes known... all that jazz. as a member of the public it seems like these things were just thrown out there. the tsa is covering their butt by doing whatever is possible, a few scanner manufacturers are having a good year, and we're just supposed to leave it like that, keep calm, carry on... i can't say that makes me feel great.
See here for a bunch of things to read (http://en.wikipedia.org/wiki/Backscatter_X-ray#Health_effect...). According to this page, 42 minutes of ordinary living is sufficient to give you a similar dose of ionizing radiation compared to the backscatter machines. It's certainly possible that the FDA is lying to us, but it seems more likely that these machines are indeed harmless. Sounds to me like the people saying "I avoid things until I'm sure they don't cause cancer" are throwing science to the wind and embracing a line of thought they wouldn't if they didn't already have some other reason for opposition.
I suppose it's possible for someone to be genuinely concerned over these very small quantities of radiation. But it strikes me that for the average person what underlies the panic is
1. a counter-factual belief that more health-harm is done by a new technology than actually is,
2. a diversionary appeal to concern for safety when health risks are not really a significant negative of a new technology.
This happens in all kinds of areas. Artificial sweeteners, GMO foods, irradiated meat products, and vaccines have all fought or are fighting this battle. The only reason this type of thinking is given a pass here or anywhere reasonable people congregate is because the community is so opposed to the technology for other reasons.
This might sound like a good thing, but it also means that the radiation isn't "diluted" over the full mass of your body. The damaging effects will be localized to -- and concentrated within -- the skin and shallower tissues. So those organs affected are getting a dose that's disproportionately much higher than the guidelines for full-body dosage considers.
Think of each cell in your body as a dice. When a cell is hit by radiation, the dice is rolled - you get cancer if any dice comes up 6 (these are billion-sided dice). The radiation dose is the number of dice rolls you need to make.
Now, under which circumstance is a roll of 6 more likely? If you roll 100 dice 1 time each (traditional x-ray), or 1 dice 100 times (backscattered xray)?
Edit: Maybe this is incorrect when it comes to cancer risk, but I had the impression it still mattered, with multiple impacts in the same area of DNA causing things to be more likely to permanently break. Unless that is extremely unlikely to happen at all at this level of dose.
Still, these machines are probably not particularly harmful.
Backscattered X-rays are not remotely near that point.
edit: Just want to respond to this: I had the impression it still mattered, with multiple impacts in the same area of DNA causing things to be more likely to permanently break.
This is called the multiphoton effect. It's real, but it's more important for radiation by low frequency radiation (e.g., cell phone microwaves). You can observe this in gases with high powered lasers or microwave resonating cavities. Weird things happen in this regime, such as stabilization (more radiation -> less ionization).
I suppose you could have molecular effects from multiple photons (e.g., one photon damages the DNA, a second damages the repair mechanism), but this is vanishingly unlikely at the doses we are discussing.
The same radiation distributed through the body will cause fewer errors per strand and be corrected.
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 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.
: 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)
The eventual outcome of a policy of assuming things are not cancer risks until proven otherwise is cancer. It is much more sensible to assume a cancer risk until proven otherwise.
You're also exposed to a variety of radiation when you fly in the high atmosphere or eat a banana. It doesn't mean additional radiation from insufficiently tested machines is a good idea.
OTOH apparently there is evidence that cell phones actually prevent cancer, so go figure.