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Comment by maninthemirror | Hacker News Reader

You are understating the risk from backscatter radiation. Because the radiation is sent in a burst, and targets skin tissue, the DNA damage may be far greater than a similar dose of cosmic radiation.

You are also assuming that the backscatter machines are functioning properly and aren't overdosing people.

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  Because the radiation is sent in a burst, [..] the DNA
  damage may be far greater than a similar dose of cosmic
  radiation.

People keep repeating that, but it is not simply true. DNA can get damaged when a single photon excites an electron and consequently influences the molecular structure. The chances of multiple photons operating on the same electron at the same time, even in cases of a radiation burst, are negligible. The person is affected by the same number of photons, which results in the same number of chances of electrons being excited. The number of excited electrons will be equal and the resulting damage will be equal.

Now it may matter that the damage is more localized in both space and time, but no one has shown this. Firstly space: spreading the radiation over only the surface, for instance 1/10th of the body (remember that surface times a small depth is always a relatively large part of a volume), means 10 times as much damage. But if the average amount of damage in the skin was one broken bond per 1000 cells, it will now be one broken bond per 100 cells. As the repair takes place per cell, that doesn't change anything for the total chances to get cancer. Only if the amount of damage in a single cell, and close enough to each other to be relevant, changes, then this type of operation may pose a problem.

Secondly for time: everything depends on the amount of time it takes a cell to repair DNA damage. If the average time of repair takes 3 seconds, then during a flight, some damage will be repaired before other damage takes place. The backscatter machine delivers its dose faster and damage may accumulate. However, if repair takes 30 minutes on average, the difference is again neglible.

The point is not that I know the numbers: the point is that people making claims don't know them. They are just claiming things that seem to make sense to them, when they draw an analogy with a car crash or something. They don't understand what is actually involved.

A single backscatter X-ray scan gives a radiation dose of 0.009 mrems, about the same as eating a banana.

http://en.wikipedia.org/wiki/Banana_equivalent_dose

Don't get me wrong, I'm opposed to the scanners as much as anyone for privacy reasons and general pointlessness. But I'm seeing a lot of bad science thrown around here.

You're not comparing bananas to bananas.

As I understand, the limited information that has been publicly released about the backscatter machines is a useless measurement when you take into account how they actually work. You can't apply a standard measurement from a medical x-ray machine that targets a small part of your body using one technique to a different machine that targets your entire body using a different technique.

So the two problems are:

1. You don't have good numbers to even evaluate how dangerous they are, many evaluations, including possibly the article above, are useless because they don't have the real data to compare to.

2. The radiation exposure from a banana also effects your body differently than a medical x-ray machine which is in turn different from a backscatter machine targeting your entire body.

I'm not saying people aren't trying to evaluate the actual risk in good faith. I'm saying they're skipping the step where we get useful numbers from the manufacturer of the machine to even apply good science to.

Edit: by "whole body" I mean "whole surface of your body" since it's concentrated on your skin

While I might agree that the worried about an X-ray scan are overblown (I assume that is your position), that number is looking at a whole body number. Part of the argument is that the amount may be significantly higher because the dose is concentrated near the surface of the skin, rather than across the whole body like cosmic ray and chest X-ray exposure.

So instead of being equivalent to eating a banana, it's probably equivalent to mashing one up and using it as skin cream.

In other news, millions of small children who enjoy playing with food exposed to RADIATION! Are bananas safe for your children?

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