Backscatter x-rays

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agelessdrifter
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Backscatter x-rays

Postby agelessdrifter » Mon Nov 22, 2010 8:55 pm UTC

They seem to be all the hubbub right now in the news with the airport security and whatnot. But I though I had heard somewhere at some point that there's essentially zero chance of them causing any sort of harm to a human because they use much weaker radiation than other common things humans are exposed to that don't do us any harm. I don't remember much about it, though. So, on a scale of 1 to Tinfoil, how silly is it to get worked up about radiation exposure from backscatter x-rays?

I did a search of the science forum for variations of backscatter xray security and nothing came up, so I hope this isn't a repost.

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Re: Backscatter x-rays

Postby gorcee » Mon Nov 22, 2010 9:05 pm UTC

The problem with the devices is three-fold:

a.) we don't actually know what the radiation flux is, because stats on the machines have not been released.

b.) The radiation is only absorbed by the first few centimeters of the body, which has to factor into safety calculations. Whereas cosmic radiation, etc, can be considered over the entire volume of the body, the backscatter X-rays cannot. X-rays themselves are also very harmful. There's a reason why the dentist hauls ass into another room before shooting radiation at your face.

c.) Because the devices are closed, there has been no independent review to ensure their safety and to evaluate the effects of possible hardware/software defects. In other words, there's no guarantee that a Therac-25 incident won't occur, because no one knows what hardware/software interlocks the devices may or may not have. What is known is that the devices scan the whole body quickly, which means they emit a high-energy pulse. What's to prevent the machine from localizing that pulse in one region of the body? Is it even possible? Is there cause for concern? No one knows, because the TSA/FDA has not allowed for independent review of the devices.

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Re: Backscatter x-rays

Postby thoughtfully » Mon Nov 22, 2010 10:05 pm UTC

You also need to distinguish them from the millimeter-wave scanners, which use no ionizing radiation.

The Xray machines have similar effects to medical Xrays, for a given dose. The dose is much lower, but the risk accumulates. What the operators are exposed to is not very clear. Frequent fliers or crew are going to get a lot more exposure than the average traveler, in addition to what they already get from extra cosmic ray flux. Pilots recently got let off the hook, but the rest of the crew gets the same exposure, so that isn't really fair.

Last week's Science Friday discussed this topic in some detail.
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Re: Backscatter x-rays

Postby Telchar » Mon Nov 22, 2010 10:29 pm UTC

According to this the FDA imposes a limit of .1 microSievert per scan for backscatter x-ray machines which is equivalent to a few minutes of flight time on longer flights. Also note the FDA says that this is based on "as low as reasonably achievable".

Without looking at the machines specifically we won't know for sure but even if the FDA estimate were doubled it would still be less than a flight from LA to NY in terms of radiation exposure.
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Re: Backscatter x-rays

Postby agelessdrifter » Tue Nov 23, 2010 12:40 am UTC

Well those are some interesting answers -- not really what I expected to hear at all. So in general, the *supposed* exposure is less than what you'd expect to get just from riding on the plane to begin with, but the real issue is that no one is letting the proverbial "us" take a look at them to verify that that level of exposure can be expected not to fluctuate, and that errors aren't likely, etc.

Also, I guess it makes sense that being higher in the atmosphere would increase exposure to cosmic rays by a bit, but it never occurred to me that it would be by any considerable amount.

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Re: Backscatter x-rays

Postby ++$_ » Tue Nov 23, 2010 12:57 am UTC

The only concern I have with the things is the possibility of a malfunction, which is always there, and can be very serious with radiation because no one really knows how much radiation is being emitted until it's too late to do anything about it.

Given that there are millimeter wave scanners which are Pretty Damn Safe, I don't see the need to use anything that produces ionizing radiation.

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Re: Backscatter x-rays

Postby Sagekilla » Tue Nov 23, 2010 1:32 am UTC

My concern is with the fact that racial profiling can be quite lethal now. My dad is Filipino, and
he gets pulled to the side to do the security checks all the time. Normally this wouldn't be a problem,
but the company he works for flies him out probably 2 - 3 times a month.

If malfunctions do occur, like ++$_ said, or if these things can actually cause a dangerous level of
emission then that puts my dad at a higher risk of developing cancer.

Just hits a little too close to home for me.
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Re: Backscatter x-rays

Postby Korrente » Tue Nov 23, 2010 3:22 am UTC

Telchar wrote:Without looking at the machines specifically we won't know for sure but even if the FDA estimate were doubled it would still be less than a flight from LA to NY in terms of radiation exposure.


My concern is that I'm a pilot, and I don't want to get the LA to NY dosage on the ground in LA, then get it again flying from LA to NY, then get it again in NY coming back inside the airport, then get it again flying from NY to LA, every day.

Honestly I have a feeling you're going to see more airports hiring private security and kicking the TSA out, which they can do (as long as the TSA 'oversees').


Edit: In looking for a link, I saw a newer article saying airline pilots are to be exempt from the security again starting next year. Whew.

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Re: Backscatter x-rays

Postby Zamfir » Tue Nov 23, 2010 6:58 am UTC



My concern is that I'm a pilot, and I don't want to get the LA to NY dosage on the ground in LA, then get it again flying from LA to NY, then get it again in NY coming back inside the airport, then get it again flying from NY to LA, every day.


The limit isn't three same as a flight, it's a few percent of a flight. In principle at least, that limit in uSv already takes the effect of concentrated radiation in the skin into account.

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Re: Backscatter x-rays

Postby LaserGuy » Tue Nov 23, 2010 3:40 pm UTC

agelessdrifter wrote:They seem to be all the hubbub right now in the news with the airport security and whatnot. But I though I had heard somewhere at some point that there's essentially zero chance of them causing any sort of harm to a human because they use much weaker radiation than other common things humans are exposed to that don't do us any harm. I don't remember much about it, though. So, on a scale of 1 to Tinfoil, how silly is it to get worked up about radiation exposure from backscatter x-rays?

I did a search of the science forum for variations of backscatter xray security and nothing came up, so I hope this isn't a repost.


I think the radiation issue is generally overstated in the media. A lot of people think something along the lines of "radiation = cancer" and don't consider issues of dosage or frequency of dosage. As others have pointed out, for a normal person, the dosage that you get from the x-ray machine isn't really that significant (assuming it is working properly). For a person who is flying several times per week, the extra accumulated dosage in addition to that of flying could start becoming a more serious concern. Pilots (now exempt) and flight attendents have been advised by their unions to opt out of the scanners. There was a quote on the thread in News and Articles on this, however, that suggested even if the dosage was something like (1/100000), it would still result in 8 cancer-related deaths per year. I can't comment on the varsity of the stat, but that would make it 8 people more than the average number of people who die in aviation-related terrorist attacks in a given year...

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Re: Backscatter x-rays

Postby Moose Hole » Tue Nov 23, 2010 4:11 pm UTC

I don't have any problem with the radiation but the fact that they can look at my tiny penis makes me uncomfortable.

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Re: Backscatter x-rays

Postby Ninjendo » Wed Nov 24, 2010 3:43 am UTC

Zamfir wrote:The limit isn't three same as a flight, it's a few percent of a flight. In principle at least, that limit in uSv already takes the effect of concentrated radiation in the skin into account.


I think the argument over danger is that the sievert is being misused- the effective dosage is being calculated using whole body, not skin absorption. See, for instance- http://www.npr.org/assets/news/2010/05/17/concern.pdf

The FDA's response letter goes into more detail http://www.fda.gov/Radiation-EmittingPr ... 231857.htm. The FDA response seems to indicate that the dose to the skin is twice the effective dose.

Does anyone know what the effective dose to skin of cosmic rays on the flight would be? I would think the dose would be higher to more dense material. How about effective doses to testicles and breast tissue, which are right near the skin?

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Re: Backscatter x-rays

Postby Minerva » Wed Nov 24, 2010 8:18 am UTC

thoughtfully wrote:The Xray machines have similar effects to medical Xrays, for a given dose. The dose is much lower, but the risk accumulates. What the operators are exposed to is not very clear. Frequent fliers or crew are going to get a lot more exposure than the average traveler, in addition to what they already get from extra cosmic ray flux. Pilots recently got let off the hook, but the rest of the crew gets the same exposure, so that isn't really fair.


b.) The radiation is only absorbed by the first few centimeters of the body, which has to factor into safety calculations. Whereas cosmic radiation, etc, can be considered over the entire volume of the body, the backscatter X-rays cannot. X-rays themselves are also very harmful. There's a reason why the dentist hauls ass into another room before shooting radiation at your face.


Why does the dentist move to another room before firing the x-ray tube? As you probably know, it's because it's not significant for you to get that radiation dose on rare occasions when you have an x-ray, but it is potentially a significant dose for the dentist, who is doing it multiple times every single day over and over again.

Similarly... I don't think 100 nanosieverts from backscatter imaging is significant for most passengers... but I think it should be evaluated quantitatively as part of the overall ionizing radiation dose that airline crew get.

gorcee wrote:a.) we don't actually know what the radiation flux is, because stats on the machines have not been released.

c.) Because the devices are closed, there has been no independent review to ensure their safety and to evaluate the effects of possible hardware/software defects. In other words, there's no guarantee that a Therac-25 incident won't occur, because no one knows what hardware/software interlocks the devices may or may not have. What is known is that the devices scan the whole body quickly, which means they emit a high-energy pulse. What's to prevent the machine from localizing that pulse in one region of the body? Is it even possible? Is there cause for concern? No one knows, because the TSA/FDA has not allowed for independent review of the devices.


I'm sure that there is real regulation of these devices by the FDA, or the NRC, or whoever is in charge of health physics regulation in this context in the United States. All the technical information regarding a proprietary machine does not need to be released to the public for that regulation to occur.

So, is what you're saying, basically, that a relatively low energy x-ray (10 keV or something, relatively low, which is what I understand that these machines use) should be assigned a higher Q factor (quality factor, for different types of radiation), than is generally assigned to x-ray or gamma photons?
That's a fair question, and I guess it's a question of broader relevance to health physics than just x-ray backscatter imaging.

I wonder if anyone has posted a question on the Health Physics Society's "Ask an Expert" webpage about backscatter imaging?

Korrente wrote:My concern is that I'm a pilot, and I don't want to get the LA to NY dosage on the ground in LA, then get it again flying from LA to NY, then get it again in NY coming back inside the airport, then get it again flying from NY to LA, every day.


Apparently, commercial pilots in the United States have the highest occupational on-the-job ionising radiation doses of any occupation - not people that work in the nuclear energy industry, for example, as many people might think. I read that once, not 100% sure if it's true.

Do professional pilots wear dosimeters or anything like that to measure their occupational ionising radiation dose? Serious question.

If pilots use dosimeters, I think they should carry them during backscatter x-ray imaging (if they go through that) as well as on the aircraft, so that the dose from that is counted towards their occupational radiation dose above background.

Moose Hole wrote:I don't have any problem with the radiation but the fact that they can look at my tiny penis makes me uncomfortable.


I don't agree with the use of this technology on ethical and privacy grounds, but is interesting to discuss the health physics side of the issue, which is a separate thing.
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Re: Backscatter x-rays

Postby ++$_ » Wed Nov 24, 2010 10:15 pm UTC

Minerva wrote:I'm sure that there is real regulation of these devices by the FDA, or the NRC, or whoever is in charge of health physics regulation in this context in the United States. All the technical information regarding a proprietary machine does not need to be released to the public for that regulation to occur.
I'm sure they are regulated, but that doesn't mean they are regulated effectively. These machines are awfully close to the untouchable sacred cow of national security, and if a report comes out that they are unsafe in some way, you can bet that the various security agencies will do their best to get that report quashed.

Also, unlike medical X-rays, these machines are owned and operated by people who don't have a significant stake in the outcome. At least in theory, a doctor is trying to help her patients stay healthy, and she thinks about the negative effects of radiation (including the chance of a malfunction) when she orders an X-ray. The TSA scanners are operated by very bored security workers who don't give a shit about the people going through the scanner, aren't trained to understand the potential health effects, and whose main goal is making sure they are not part of the team that lets through the next terrorist.

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Re: Backscatter x-rays

Postby Antimony-120 » Fri Nov 26, 2010 2:47 am UTC

Minerva wrote:Apparently, commercial pilots in the United States have the highest occupational on-the-job ionising radiation doses of any occupation - not people that work in the nuclear energy industry, for example, as many people might think. I read that once, not 100% sure if it's true.

Do professional pilots wear dosimeters or anything like that to measure their occupational ionising radiation dose? Serious question.

If pilots use dosimeters, I think they should carry them during backscatter x-ray imaging (if they go through that) as well as on the aircraft, so that the dose from that is counted towards their occupational radiation dose above background.


That doesn't actually surprise me, although my guess would actually have been miners (in certain seams, particularly coal). People in the nuclear industry often actually end up working in some of the lowest levels of background radiation just because the shielding that protects them from the radiation in the core also serves to protect them from the normal background radiation. Although that doesn't mean their job doesn't bring them into contact with radioactive materials, it's an odd little point.
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