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Thread: Radiation Protection

  1. #1
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    Radiation Protection

    Sources of Radiation exposure

    There are perhaps three types of radiation exposure that we are concerned with…that from a nuclear detonation (bomb), a reactor accident (Fukushima, Three Mile Island, Chernobyl), or a ‘radiological dispersal device’, RDD, or ‘Dirty Bomb’. Each is different in its materials, and effects.

    The decay from a nuclear power plant reactor breach is quite different from the decay from a nuclear detonation, because the materials used are quite different. Quite a bit of trouble is taken in building nuclear weapons to make certain only the ‘right’ materials are in them, for efficiency and physics reasons. Because of the nature of a reactor, there are lots different types of radioactive materials being transmuted (converted from one element to another, with the release of energy). Some of those new materials are themselves used in the nuclear processes while some are not. The effects of a so-called 'dirty bomb' are different still, mainly because most dirty bombs would be made with only a single, non-chain reacting radioactive material.

    Secondly, fallout is radioactive material, stuck to (mostly) dirt, following a nuclear detonation. After a reactor accident, you may well have radioactive contamination, which is different - it is melted radioactive material being blown around by the wind.

    A small difference? Not really. In a nuclear detonation, there is a massive heat bloom caused by the detonation (itself reaching temperatures approaching 10-million degrees C), that heats the air up tremendously. Hot air rises, and the resulting fireball, vertical column and mushroom cloud sucks fallout up into the upper atmosphere (the stratosphere) where it gets blown around by the jet stream and other global weather patterns. In a reactor accident virtually none of the nuclear fuel, and only very small quantities of radioactive byproducts gets blown around Following the reactor accidents in Japan, the radiation that was detected on the west coast of N. America was in such small amounts as to be truly negligible – we have the technology to detect far smaller quantities of radiation than can likely harm us.

    Consider if material from Japan had entered the stratosphere (and the jet stream), it would have reached the west coast of N. America in about a day. Since we know it didn't (it took around 8 days (at an average wind speed of around 21 knots (25 mph) and a distance of 4300 nautical miles (almost 5000 statute miles) to be detectable in the west coast) we know it wasn't up there in the fast lane. The vast majority of the radiation and contamination from Japan is going into the ocean, bad for the Japanese (how do you think we got Godzilla?); but not so bad for the rest of us...once the stuff settles to the bottom, very diluted, it will be covered with sludge and not be much of a practical factor...all the while decaying.

    In the Chernobyl disaster, the reactor used giant blocks of graphite as the control for the nuclear process (a very different type of reactor, with different internal components, and no containment building around it at all). When it got out of control, that graphite started burning, becoming basically a giant barbecue (graphite is one crystalline form of carbon, coal is a non-crystalline form of carbon, diamond is another crystalline form of carbon, get them hot enough and they all burn). The radioactive fuel and byproducts mixed with burning graphite was the contamination that blew around Europe.

    Even with that, the only deaths that can be positively attributed to the disaster are those of the workers who were sent in to try to control it (they were screwed). We can estimate that perhaps 300 more total deaths over the lifetime of everyone who was alive at that time will occur because of the radiation exposure, but we can't say who or when. We do know that at least 300 people who were nearby have committed suicide because of their fears (not for any actual physical reason relating to the disaster).

    However, the vast majority of both contamination and fallout tends to settle near the source, downwind, because they do not go up high, and radioactive fuel materials tend to be quite heavy. Therefore, they do not go far.

    Radioactive Decay and the 7/10 rule

    For nuclear detonations, for every 7-hour period after the peak in radiation, the intensity of radiation fallout will decrease by 10%. So, say a detonation peaks at noon, and your handy survey meter says that it's 1000 R/Hr outside (very bad news, which is why it better be outside). At 1 PM, the l000 R/Hr level will have decreased by 10%, to 900 R/Hr. Still, pretty damned bad. Another hour, 2 PM, and the level has gone down 10% more (to 810 R/Hr), and so on. There are several spreadsheets around that people have made to do the math, you can search the net for them. I like the ones made by "Jerry D. Young”, and "TOM" (Tired Old Man), two prolific writers of PAW fiction.

    To make life simple, you can assume that the radiation after a nuclear detonation has gone down to 10% of what it was originally after 7*7 hours (49 hours, or 2 days and change). That would mean in our example, 100 R/Hr, still pretty bad, 50% of the people who were out in it for an hour would have symptoms of radiation exposure (not really bad symptoms, but still....) and a lifetime increased risk of cancer. 2 hours and 50% would be sick, 6 hours and most of them would be dead in a month.

    After 7*7*7 hours, 343 hours or 14 days and change, it will have gone down to 1% of what it was (1 R/Hr). At this point, you can decide if there is something (taking care of animals, getting food, water or other supplies, throwing out the trash, burying the dead) is worth the risk. An hour or two probably won't hurt much, but you still can't spend all day in it (24 R/day over 8 days is 200 R).

    After 7*7*7*7 hours, 2401 hours or a around 100 days, (a bit more than 14 weeks or 3 months) the level outside will be down to 0.1% of what it was (0.1 R/Hr). This is probably an OK level to go outside, work, salvage, grow food, etc, but I'd still sleep in a shelter at night, for another 6 months to a year or so. BTW, children (especially infants) should NOT be casually exposed to radiation, or even contaminated soil after a detonation...their entire body is closer to the source, the ground, so they get a higher whole-body dose.

    If you are close enough for the shock wave of a nuclear detonation to hit you (call it within 5 miles, there are few very large warheads today because it doesn't make any sense to build them), you will probably have other issues to deal with - like surviving the blast waves (there are at least two, one rushing away from the detonation and another blowing back to fill the hole, and it's the second one that does the most damage).

    But, you can expect fallout to start almost any time, and being close it will be quite heavy. You can calculate the time it will take by estimating the wind speed, if the wind is blowing 10 mph and you're 5 miles downwind, it will take 1/2 hour to get to you. Pretty simple. You can also figure out where a detonation was by how long it takes for the fallout to reach you, based on wind speed and direction...if the wind is 10 mph from the west, and it takes 24 hours from the time you know a detonation occurred until it gets to you, it was 240 miles to your west.

    The best thing to do if you feel the shock wave or see the detonation is to move crosswind as quickly as possible for however much time you think you will have, until you reach a good shelter. A keychain radiation detector (NukAlert or similar) may be useful in this regard, merely detecting radiation does not mean you will be affected adversely by it.

    For a reactor accident, the individual components of the reactor core (which is changing all the time) have to be calculated...but you have to know what they are to begin, so there is no calculation you can do ad hoc.

    A good shelter might be a deep basement with good cover, or even the upper stories of a tall building (not the upper 3 or lower 5 floors, you want at least some distance between horizontal surfaces where fallout might accumulate and you).

    The book Nuclear War Survival Skills was written in the 1980's and has many plans for good, self-made fallout shelters, even ones made on the fly. It is available here for free: http://www.oism.org/nwss/index.htm

    Note: The first aid info given there is pretty badly out of date. The rest of the information is mostly OK.

    There are old US Government Civil Defense booklets on line about how to build a shelter into your existing home, or find the amount of mass you need to halve the radiation exposure for different kinds of construction materials. For example a shelter with 3' of packed earth roof provides a factor of 10 halving thicknesses or 1/2^10 (1024), that is 1/1024th as much radiation as outside. In my home, we got a little carried away. We have 3' of packed earth, and wound up with 24" of reinforced concrete as well; another 2^10, for a total of 2^20 or a factor of a million and change. We get more radiation from the concrete (it's naturally radioactive) than we would from a 1000 R/Hr point source outside...and it didn't cost that much more than building the basement did without it.

    One thing the Government has recently said is that in the event of a 'dirty bomb', the best thing to do would be to stay indoors (shelter in place) for a few days. You wait until the outsides are decontaminated (mostly flushed off); so having a weeks’ worth of food, water, and sanitation capability in a simple shelter would be a good thing.

    http://www.theatlantic.com/national/...d-cover/68776/


    Good luck!

  2. #2
    Do you have a robot?
    realist's Avatar
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    Thank you doc for the information. Now you have tweaked my interest I'm going to research the FEMA training.
    If it is predictable then it is preventable....... Gordon Graham

    So if it is predictable and preventable then you better prepare.

  3. #3
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    Thanks for the post. The link for the book does not seem to work.

  4. #4
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    I just tried it and it worked for me....


    And I just realized I made an arithmetic error. The 7/10 rule is that for every 7 fold increase in time, the radiation decreases by a factor of 10, not 10%


    https://emilms.fema.gov/IS3/FEMA_IS/is03/REM0504050.htm

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