There's all kinds of FUD surrounding these devices, and it seems like many with health concerns are engaging in motivated cognition. For example: if the dose is concentrated in the skin, couldn't that be a good thing? Our skin is constantly bombarded with ionizing radiation. UV rays, alpha and beta particles, etc. When it comes to these sorts of insults, the skin is one of the most resilient organs.
According to the FDA, the dose to the skin is 89,000 times lower than the annual limit. If backscatter scanners caused harm, it would tell us something new about physics, biology, or both.
Are backscatter scanners an invasion of privacy? Yes. Are they a waste of money? Almost certainly. Do I wish airports got rid of them? Yes. But unless our understanding of physics and/or biology is very wrong, they're not dangerous.
> "For example: if the dose is concentrated in the skin, couldn't that be a good thing? Our skin is constantly bombarded with ionizing radiation. UV rays, alpha and beta particles, etc"
Alpha particles only travel a few cm in air. Beta particles may travel around a metre. Unless someone works with radiation, I cannot imagine how anyone's skin is constantly bombarded by these types of particles.
Also, any form of ionising radiation is generally accepted to be A Bad Thing. To suggest that it could possibly be good seems ludicrous. Even UV rays are generally accepted to be harmful and I'm sure most people would understand that they're supposed to limit their exposure.
Edit: Or did you mean to say that dumping it in the skin might be better ('a good thing') compared to spreading throughout the body? Either way, it's not a medical procedure so there should be no need to use it at all imho.
>Edit: Or did you mean to say that dumping it in the skin might be better ('a good thing') compared to spreading throughout the body?
Your interpretation is correct. I'm with you: all else equal, I'd prefer to be exposed to no extra ionizing radiation. I was just pointing out that many of the health arguments seem like motivated cognition to me, and showing how one can be reversed.
>Unless someone works with radiation, I cannot imagine how anyone's skin is constantly bombarded by these types of particles.
I meant that our skin is constantly bombarded by ionizing radiation, not necessarily that it's constantly bombarded by alpha and beta particles. I'm not sure how much alpha or beta dose the average person gets. While the particles themselves don't travel far, they can be formed in many ways. As klodolph has said, radioactive decay is one source. Alpha and beta emitters show up in some surprising places: smoke detectors, anti-static coatings, and emergency lighting systems.
Also, any form of ionising radiation is generally accepted to be A Bad Thing. To suggest that it could possibly be good seems ludicrous. Even UV rays are generally accepted to be harmful
UV rays in sunlight are used by the body to synthesize Vitamin D - they can be good for you.
> Yes. But unless our understanding of physics and/or biology is very wrong, they're not dangerous.
Our understanding of the relationship between low-level doses of radiation and cancer is frighteningly incomplete -- to the point where it's not even certain that the cancer rate doesn't go down when low level radiation increases. This is nothing more than an appeal to authority -- the FDA makes the policy, not the science.
> Yes. But unless our understanding of physics and/or biology is very wrong, they're not dangerous.
Our understanding of the relationship between low-level doses of radiation and cancer is frighteningly incomplete
This is what especially steams me when I talk to "experts" about this. (In quotes because what most doctors know about radiation and cancer is pretty shallow in the grand scheme of things.) It's like all they hear is "someone afraid of radiation" and it's like they can't even comprehend the geometric argument I'm making and then go on to quote data and heuristics based on the wrong energy deposition geometry. Also, they tend to talk about the relationship between cancer and radiation dose as something that's well understood. Well, maybe it is for chest X-rays and other specific situations for which we have lots of data, but this situation is different from those in an interesting way -- one which should bring questions to a scientific mind.
Where the experts have a mental blind spot such that they can't even find or formulate a cogent argument that actually applies to what you're saying, there might be something that needs to be looked into.
> When it comes to these sorts of insults, the skin is one of the most resilient organs.
Why do we think know that? Because of data from conventional X-rays that have a totally different geometric assumption. (Energy distributed throughout the body volume.) What we know of cancer at the level of mechanisms inside the cell suggests that the living part of skin that constantly divides to replace cells is more prone to cancer than other tissues.
> The FDA is notoriously risk-averse, but it has done studies on the safety of backscatter devices and concluded they're safe
The web page you pointed to just mentions "low dose" and compares the dose to "Naturally occurring ionizing radiation." Well, duh, I know this already. Most naturally occurring ionizing radiation deposits its energy evenly throughout the body. It doesn't address the new geometry of energy deposition. Show me one study that does! Show me one government document that does!
Again, it's "spherical cows" assumptions applied to public health! As a technically adept person, this should raise your suspicions! I'll grant you that the risk is probably low, but without more research into the same energy deposition geometry, you're handwaving public health.
I agree with your parent comment based on other information (details below), but I think his argument is wrong, or at least unsubstantiated. I was curious where his information was coming from, so I searched for some of his vocabulary. I googled for these things:
* backscatter cancer +"geometry of the delivery"
* backscatter cancer +"geometry of delivery"
* backscatter cancer +geometry
I didn't find that's how anyone talked about the risks, and so on that basis alone, I found your argument more compelling. However, I did find information that furthers the anti-backscatter argument in the same way you argue the pro, that is quantitative studies:
"research studies have concluded that a small number of cancer cases would result from scanning hundreds of millions of passengers a year."
This paper doesn't talk about the geometry of exposure, but it does say that while the machines are basically safe, it also uses statistics to show that:
* "there will be some cancers induced by the associated radiation exposure" (billions of scans means definitely some cancer)
* "risks will be somewhat higher for children, for radiosensitive individuals, and, particularly, for aircrew and frequent fliers."
* these machines may cause cancers cause by malfunctions
So, if you believe the machines will kill a few hundred people or the terrorists will kill a few hundred people, shouldn't we just save our money, and our liberty? I don't think it's just an inconvenience - I think it's a bunch of needless cancers.
No, I am not trolling. Please try to read comments more charitably instead of assuming malice. Yes, I was comparing skin dose to the annual limit for the whole body. Depending on what you count as skin, skin is 2-5% of an adult's mass. So it would take thousands of scans per year to exceed the dose limit. In other words, safe.
I know what a sievert is (your definition is incorrect) and I know different types of ionizing radiation affect different tissues differently. But the safety margin is so great (89,000!) that it would take a new mechanism of action for such a tiny dose of X-rays to cause disease.
Edit: Because you deleted your comment, other readers now have no clue what I responded to. :/
> Sv is 1 joule of radiation absorbed for every kg of a person's weight, but that 1 joule could come from alphas, betas, gammas, or x-rays. It may be a fixed amount of energy, but whether it comes from photons or electrons or positrons or helium nuclei is _IMPORTANT_.
No, that's factually incorrect. You're thinking of the gray (Gy), which is 1 J/kg no matter what. 1 J of gamma absorbed is 1 Gy and 1 Sv, but 1 J of alpha absorbed is 1 Gy and 20 Sv. 1 Sv of neutrons is only 0.1 Gy.
It doesn't help that they are dimensionally equivalent, so there's a proliferation of unit converters which consider the conversion to be 1.0 always.
> Unless someone works with radiation, I cannot imagine how anyone's skin is constantly bombarded by these types of particles.
Depends. Some people have granite countertops in their kitchens which give off Radon, an alpha emitter. (Not all granite does this.)
But instead of arguments, we can look at the evidence. The FDA is notoriously risk-averse, but it has done studies on the safety of backscatter devices and concluded they're safe: http://www.fda.gov/Radiation-EmittingProducts/RadiationEmitt...
According to the FDA, the dose to the skin is 89,000 times lower than the annual limit. If backscatter scanners caused harm, it would tell us something new about physics, biology, or both.
Are backscatter scanners an invasion of privacy? Yes. Are they a waste of money? Almost certainly. Do I wish airports got rid of them? Yes. But unless our understanding of physics and/or biology is very wrong, they're not dangerous.