Radiation facts and myths

Discussion in 'Off The Beaten Track' started by rfisher, Mar 14, 2011.

  1. rfisher

    rfisher Satisfied skating fan

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    There's been a lot of concern about the events taking place in Japan with the nuclear reactors. The media is really mixed in it's reporting, but much of it is designed to be sensational rather than educational or factual. I am a medical imaging program director with all sort of initials behind my name that don't mean a lot to any of you. I teach radiobiology and radiation physics. I'm responsible for ensuring 50 students a year understand radiation safety for themselves, their patients and the general public. All that is to provide professional background. Most people are afraid of radiation, yet most really don't have any understanding of what it means. Just this week one of my students had a patient get very upset when she left her glasses in the room after a chest x-ray. She was convinced they were now radioactive. So, I'm going to post some basic information about radiation dose and what that means from a biologic perspective. Feel free to post questions and I'll try and answer. I will leave answers regarding the physical aspects of the nuclear plant to a couple of poster who actually work at such facilities, but feel free to post those questions as well.

    1. All ionizing radiation has the potential to cause biological harm. That includes UV and infrared light, x-ray, particulate radiation and gamma rays (what's coming from the reactors). Potential is the key. The probability of any harm actually occurring is dependent on how much radiation (dose) is received, to what body part (whole body vs. selected organs), and the quality of the radiation. I could take a piece of Polonium-218 and put it on my desk, cover it with a piece of paper, and receive no radiation. However, if I swallowed that piece of Polonium, I'd probably die because of the severe damage to my GI tract. This is what killed the Russian spy several years ago. That's because the radiation produced by Polonium has a very high rate of transferring it's energy to tissue, but it does it within a couple of millimeters. Gamma radiation, OTOH, has a relatively low rate of energy transfer, but it has a significant range (distance) in which to do so.
    2. How far can it travel? It depends. The gamma ray will interact with the air in which it is traveling. It ionizes or causes an electron to be removed from atoms it encounters. The greater the distance it travels, the less energy it has when it encounters something else. It's the transfer of energy along with the removal of an electron that can cause biological harm. So, the farther away you are, the less exposure you will receive. In fact, we call the Cardinal Principles of Radiation Safety : Time, Distance, and Shielding. Minimize the time of exposure, maximize the distance and shielding. Shielding is putting something between you and the radiation.
    3. What does it mean when they say levels are 8 x normal? I think everybody knows what 8 x means, so the real question is, is that bad? What's normal?
    The other basic principal of radiation safety is called ALARA which stands for As Low As Reasonably Achievable. This is the underlying principal for medical radiography as well as industrial radiation production. We want to keep any dose level as low as possible. Minimum dose levels are set by the International Commission on Radiation Protection and the National Commission on Radiation Protection (US). They base these lower than what research has taught us, sadly much from the Hiroshima and Nagasaki data along with other populations, are the dose thresholds for different biological effects.
    4. These minimum levels take into consideration radiation from multiple sources: cosmic, cosmogenic (within the Earth's atmosphere), terrestrial (radon is a prime example), naturally occurring radioisotopes etc. I'll give some sample amounts below. The real key here is that the dose limits are set well below levels of known biological effects. It is undeniable that even a very low dose, one photon, could cause a biological effect, but the statistical odds are really small. My students are always a little annoyed after I've presented all the things that could happen when they do a single chest x-ray when I conclude with the greater probability that they won't. It's always a weighing of risk vs. benefit.
    5. Some example radiation doses: if you live in France, you receive approximately 0.00071 Sieverts annually, but if you live in Austria you only get 0.00037. If you smoke you get about 0.08 Sievert to your lungs. Dose limits vary but the goal is to keep public exposure below 1milliSv/year for a total body exposure (individual organs and the lens of the eye are somewhat higher). That's less then what your lungs are getting all ye smokers. This would be based on medical x-ray exposure or anything above the natural background exposures. The exposure coming out of the plant was approximately 70 microSv on the last report I saw. Meaning somebody exposed would be well below the accepted minimum annual limit. We would not expect them to have any biological ramifications.

    I don't use Wikipedia for references, but I'll be happy to supply a list of technical journal or book references if anybody so desires. I know how some want their links. :)
     
    Last edited: Mar 14, 2011
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  2. MichaelK

    MichaelK Active Member

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    I agree with your assessment that somewhat higher than 'normal' dosages of radioactivity in a not too long time frame are unlikely to be harmful. However, in Japan it is not clear how much radioactive material escaped from the reactor and reports are conflicting in that regard. It is hard to imagine after what happened that the radioactivity in the reactor was fully contained. Fortunately the wind is blowing the stuff off to the sea for now. But I can also understand worries that the situation is more serious as is admitted by officials and a larger amount of radioactivity got released.
     
  3. rfisher

    rfisher Satisfied skating fan

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    The dose of the radiation released is very small. What would be a problem is if there was a significant quantity or someone remained in that quantity a long time which would increase their total exposure. The dose picked up by the US pilots was much less than the the normal background radiation exposure. That someone receives everyday. Now, it's prudent to remove people from receiving additional exposure (anything above background levels), but it's unlikely that anybody has received a significant dose that will cause either immediate or long term health issues. When we do a CT scan on a patient they are getting a significant increase in exposure above their background levels, yet we perform this exam everyday without doing harm. That could change if there was a massive release of radiation, but everything in the media indicates that is not the situation. Some radioactivity was present in the two explosions, yes. However, the dose would be very small.

    One thing very different in all nuclear reactors now (after Chernobyl) is that the radioactive material is contained within a separate steel container apart from the concrete containment tower that exploded due to the build up of hydrogen gas. It is a matter of keeping sufficient cooling on the rods until they cool on their own.
     
  4. MarieM

    MarieM Grumpy Cynical Ice Dance Lover

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    Just to add one thing about the ICRP (I prefer the french CIPR bah) is that you can find tons of useful information on their site. Like the annual dose received in your area and so on.

    Actually, all the recommandations of the ICRP are taken into account at the European level, like with EURATOM 96-29 and so forth. I know for sure it's the same in Japan.

    rfisher : the lastest news coming from the french safety agency is that the amount released during the explosion of number 1 reactor was approximatively 1 mSv/h for 3 hours, then it decreased and is now less than 50 ┬ÁSv/h next to the reactor facility. They are running calculations (MONTE CARLO based) to assess the amount probably rejected in the environnement.
    They are not sure however their data is accurate. They think a large amount, more than reported, has been released in the atmosphere, but wasn't on the scale of what is reported in certain press agencies. They tend to believe thanks to weather broadcast that it all went to the pacific side and not too much inland. They also state that measures are taking place at the moment in the 20 kms evacuated to evaluate the impact of the blasts.

    Just one other fact, safety agencies have got a tendency to report facts in a very negative and conservative point of view : they were created to be like that and that's very very good in those circumstances.
     
  5. dbny

    dbny New Member

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    Thanks for posting some clarifications re radiation.

    We actually do not know for a fact that no harm is done. There must be a certain number of people (be it ever so small) for whom just one CT scan happens to cause damage that results in cancer. The benefits of CT scans, in general, outweigh the risks, but fewer are better, and none is the best. Ironically, cancer patients are often given multiple CT scans over relatively short periods of time. Choose your poison.
     
  6. rfisher

    rfisher Satisfied skating fan

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    As I said, and as I teach my students, you do damage with every exposure. You do damage every time you expose your skin to the sun. UV radiation can cause skin cancer. However, there are a number of factors that determine if radiation damage is significant. What cell is hit, where it's hit, how often it's hit, whether a critical target structure is hit and so on. Most of the time a water molecule is hit and the molecule immediately reforms leaving no damage. DNA has a remarkable repair mechanism. We teach that there is no minimum dose but acknowledge the reality most all cancers have a threshold that must be crossed. That threshold dose varies considerably.
     
  7. made_in_canada

    made_in_canada INTJ

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    Thanks for sharing your expertise, rfisher.
     
  8. agalisgv

    agalisgv Well-Known Member

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    Since I don't know this area at all, I just wanted to ask a clarifying question--does MarieM's post mean that for three hours, people in the vicinity of the nuclear reactor were exposed to a year's worth of radiation exposure?

    If that's true, what would be the potential biological ramifications of that?

    Thanks for taking the time to respond :)
     
  9. rfisher

    rfisher Satisfied skating fan

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    It really depends. One would have to be standing in the reactor to receive that rate. Distance of even a meter reduces the dose by 1000. It's inversely proportional to the square of the distance. Meaning the further away you are, the less dose by a factor of 4. That minimum annual dose is exceeded by many people. Airline pilots, for example, or even people who live at high altitudes. It's an average recommended level. Biological consequences vary but the risk for developing leukemia, for example, is .1% after an exposure of .1 SV which would take almost 1000 hours of exposure at that rate, and then the risk is less than 1%. They have evacuated people living close to the facility. Even if it were to have a catastrophic radiation leak, the people who would be most impacted are the workers at the plant.
     
  10. Sylvia

    Sylvia On to GP & U.S. Sectionals!

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    Last edited: Mar 14, 2011
  11. rfisher

    rfisher Satisfied skating fan

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    It would seem so. They will have a significant issue with clean up. It won't pose a health issue to the general population, but it's going to be extremely expensive and they will have a problem disposing of the material. The cost is going to be in the billions both in loss of generating capacity and in clean up. I have to assume the Japanese environmental protection people will do whatever it takes to minimize the environmental impact. I just hope they don't opt for the dump it at sea option.

    Disposal of radioactive waste is my biggest issue with nuclear power. The US has had an ongoing battle with disposing of tons of material at the Yucca Mountain facility for years. It's been blocked in the courts several times :cheer2: but is up for discussion again. :(
     
  12. jsh5

    jsh5 New Member

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    I'm a chemist by training as well, so this has me curious about areas I don't know much about. I know that one treatment for exposure is flooding the thyroid with iodine - is the body particularly sensitive to iodine or is it just that it persists in certain organs and causes damage longer?
     
  13. Wiery

    Wiery Well-Known Member

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    Thank you very much-very helpful and thoughtful post, rfisher!
     
  14. MarieM

    MarieM Grumpy Cynical Ice Dance Lover

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  15. MichaelK

    MichaelK Active Member

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    The thyroid needs iodine for producing thyroid hormones, therefore iodine is preferably stored in the thyroid. This means that radioactive iodine will be stored as well in the thyroid where it may lead to cancer. In fact thyroid cancer is known to be much more prevalent in the Chernobyl area after the disaster - so it is a real danger.

    If people take iodine pills the thyroid is saturated with iodine and no more potentially radioactive iodine will be stored and the risk of cancer will be greatly reduced by taking the pills.
     
  16. MarieM

    MarieM Grumpy Cynical Ice Dance Lover

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    Yeah that's the main problem with nuclear programs. There is little research funded over here about what to do with nuclear wastes.
    I am not familiar about what the US is doing with its wastes, but Europe hasn't been good with it so far.
    In France they are still not sure if they'll go ahead with deep geological disposal while in Germany they just flooded their salt mines with theirs.
    And noone seems to be willing to fund real research about what we could do like transmutation. Sad !
     
  17. Anita18

    Anita18 Well-Known Member

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    From my recollection of endocrine biology, whatever iodine taken up by the body is immediately sequestered in the thyroid, and if it's radioactive, it sits in your thyroid and does not leave. Which is why they give extra iodine to people who have been exposed so their body will sequester the non-radioactive iodine first and then there's no room for the radioactive ones....
     
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  18. Anita18

    Anita18 Well-Known Member

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    I agree. I've worked with radioactive substances before and have had the discussion about how this waste is gonna sit in a deep hole for hundreds of years and it's such a waste. :(
     
  19. Ajax

    Ajax Well-Known Member

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    rfisher, thank you very much for this post. I am no scientist so all the radiation stuff they talk about in the news goes right over my head... My stupid-ass question, if you could be so kind to respond: Why exactly is everyone concerned about the power plants right now? Everyone was evacuated and supposedly didn't receive much harmful radiation. There are dangers of further explosion. Is the issue that those could cause additional gamma radiation that would travel further than the evacuation zone and put people in danger?
     
  20. dbny

    dbny New Member

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    Mine too. I was a geology major and do not believe there is any secure way to dispose of such waste for the extremely long times needed. I know there are plenty of geologists with many years of experience in the field who will testify that x, y, or z is safe. I think it's hubris.
     
  21. Polymer Bob

    Polymer Bob New Member

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    If I might interject here. It seems the news media and governmental organizations use the term "radiation" differently than physicists. The media and organizations are not so much concerned with direct neutron, alpha, beta and gamma rays; which weaken with the square of the distance. They are concerned with the release of radioactive elements into the environment. This stuff would get into the air and water and travel with the wind and currents. The inverse square law goes out the window at that point.
     
  22. rfisher

    rfisher Satisfied skating fan

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    Worst case scenerio, yes. If there was a full scale meltdown of the nuclear material there would be a huge explosion which would disperse radioactivity over a larger area. Not only would there be problems for anybody in the area, but the ground would be contaminated. It's unlikely that anybody would suffer Acute Radiation Syndrome which happens with a total body exposure of more than 2-3 Sv (that's Seivert not milliseivert and is a substantial dose), but the risk of cancers such as leukemia and thyroid would increase. Leukemia being the most common. This happened with the Chernobyl meltdown.

    One big problem that happened with above ground nuclear testing was the dispersal of Strontium-90 as part of the fall out. Strontium is uptaken in grass. Animals that eat the grass, such as cows, can pass the isotope through their milk. Prevention of that worst case is what the engineers are doing. I can't imagine the stress levels at those reactors. It's kind of like a whack-a-mole game where you hit one and another pops up. Chernobly did teach that the nuclear material needed multiple containment fields and all modern reactors have those additional safety features.
     
  23. rfisher

    rfisher Satisfied skating fan

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    The inverse square law still applies to particulate radiation. However, the dispersal of radioactive particles would be the concern. I'm not certain what material is in rods or if the decay products are alpha, beta or neutron producers along with gamma. It doesn't really matter in regard to nuclear fission (well it matters which elements you use but not whether they are an alpha producer). It's the heat given off duing the decay event that drives the steam turbines to create electricity. Each of those would have a different impact if there was widespread dispersal. Alpha particles are heavy (they are essentially helium nuclei) but have a very short range. Beta are small (essentially a nuclear electron) with a longer range. Gamma is wave form electromagnetic energy and will be dispersed by wind fairly quickly. All of which is esoteric and wouldn't matter to the impacted population if the worst happened.

    This is one of the issues associated with a dirty bomb. Most wouldn't have an explosive chage sufficient to spread the radioactive material in a wide circumference, thus the overall damage would be somewhat limited. It's the psychological damage that would be catastrophic. Not that if you were one of the people within that circumference it wouldn't be catastrophic.
    ]
    And MarieM, the US has planned to store all the nuclear waste in some expaned natural caverns beneath Yucca Mountain in the west. They carted stuff around the country for a couple of years and nobody would let them put it in their backyard. They finally made a deal to deposit it here, but so far the nothing has been done. The project has been blocked by several environmental suits. The site is in a seismically active area (quakes and volcanos) and the risk of contamination has been the basis for the courts to rule in favor of the enviornmentalists. The stuff is still sitting around in steel barrels happily corroding away.
     
    Last edited: Mar 14, 2011
  24. Yehudi

    Yehudi Well-Known Member

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    I've been using this site as the main source for info on the nuclear situation. It's a pro-nuclear industry site so of course, you don't want to be too reliant on this site (the twitter feed for the media guy makes my eyes roll), but it's been the most informative in terms of the steps being taken to cool down the reactors.

    http://www.nei.org/newsandevents/information-on-the-japanese-earthquake-and-reactors-in-that-region/

    They also have an FAQ about radiation here.

    http://www.nei.org/newsandevents/in...ctors-in-that-region/radiation-in-perspective
     
  25. PUNKPRINCESS

    PUNKPRINCESS New Member

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    Yes. Thank you.

    This is why I :rolleyes: at individuals who want to declare, definitively, that "it's safe, it's saaaaaafe, you uneducated fools."

    One of my profs compared the likelihood of gamma rays hitting an atom in the body as something like an asteroid traveling through space and hitting a planet. The amount of empty space they can travel through is relatively huge, so the probability that they will hit anything meaningful is low. And yes, the body has a number of repair mechanisms as far as DNA damage goes, and multiple changes to specific genes have to occur, irreversibly, before a cancer develops. When you try to count the odds, it seems unlikely. Yet, we know that cancer is actually common, :slinkaway which makes sense when you consider that every second we are bombarded by millions of different processes that can cause deleterious changes in the body. I'm not exactly going to stop eating my barbecued meat, but since getting CT scans or X-rays taken aren't particularly fun, why do more than you have to. :hat1: :hat1: :hat1: Even if you smoke a pack a day.
     
  26. GarrAarghHrumph

    GarrAarghHrumph I can kill you with my brain

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    I'm loving that we have our own "WTF does this all mean re: radiation" thread. FSU rocks. We do more analysis of the news than the news does!

    What does this actually mean in real person speak?

    From the BBC:

     
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  27. rfisher

    rfisher Satisfied skating fan

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    The "radiation tops legal limit" would mean the levels are higher than the maximum set by the ICRP. You'd have to know what that level is in order to assess the specific impact, keeping in mind the *legal limits* are set very much lower than the statistical thresholds for long term biological damage. So, if those levels persisted for weeks or months, it would be a problem.
     
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  28. LadyNit

    LadyNit moving right along Staff Member

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    NHK news now says that 400 milisieverts are detected around the reactor #1 in power plant#1. People are being told to stay indoors if they are within 30KM of plant #1 and to prevent air exchange between indoor systems and outdoor air.
     
  29. Anita18

    Anita18 Well-Known Member

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    Obviously, the very first thing someone should do to prevent cancer is STOP SMOKING. :p

    And stay out of the sun. :p As a general rule, you'd want to prevent as much inflammation as possible, that's where cell damage occurs.

    And thanks for emphasizing the number of DNA mechanisms. My lab does DNA repair and we have yet to really start delving into what the cell actually does when DNA breaks. It sounds simple but there's so many things going on, it literally makes no sense that someone could have designed this. :lol:
     
  30. numbers123

    numbers123 Well-Known Member

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    rfisher - what does the ladynit post mean?