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Friday, March 4, 2016

Radioactivity for Dummies

Not actually Erin.
& is used with permission.
I am a big fan of science fiction. This is noteworthy because I have trouble understanding math past basic algebra -- which therefore means I have trouble understanding the cooler parts of science. However, good science fiction (and not space opera; that's just future-flavored fantasy) will take time to explain those concepts in prose, and English comprehension is where I excel. If someone can illustrate an analogy for me, I totally get it.

(Which is, oddly enough, why I understand the basics of quantum theory: quantum mechanics are so odd that they require analogies to explain to nearly everyone, and so I grasp such things as the Uncertainty Principle without necessarily understanding the underlying math.)

And so, in order to understand things which interest me, I have to dumb them down and turn them into examples and analogies that I can understand. The good news here is that, once I've understood something, I can then explain it to other people pretty easily using the same technique.

Which leads us pretty handily to a series of articles where I attempt to explain, in my own fumbling way, what radiation is, how it works, what it does to you, and what you can do to prevent it from harming you. I'm going to assume that you've been reading along with Chaplain Tim's articles on "Chemistry for Preppers"; if not, you may find it helpful to refresh your knowledge with his posts about atomic structure and ions.

What Radiation Is
First I need to be pedantic and say that "radiation" is not the same as "radioactivity", even though people use them interchangeably.

Radiation simply means "Energy that is transmitted via electromagnetic waves without needing a medium."  The heat from the sun is thermal radiation, because it travels through space (and space is nothing, therefore it is not a medium). Compare and contrast radiation with conduction, which is where energy is transmitted directly from one substance to another (think electricity along copper wires), and with convection, which is where energy uses a medium like air or water for transmission.

Put simply:
  • If you cook a steak by putting it on a hot iron, that's conduction. 
  • If you cook it by putting it in the oven, where the element heats the air that cooks the meat, that's convection. 
  • If you cook it by focusing sunlight on it, that's radiation. 
When most people use the word "radiation" what they really mean is "ionizing radiation". How ionizing radiation works and why it's (usually) bad for humans is a post unto itself, and before I get into that, though, I need to explain a few other concepts first. For now, here is the quick and dirty definition: ionizing radiation is energy that is powerful enough to knock an electron out of its shell without a chemical reaction. This is bad because, as Chaplain Tim has explained, an ion will bond to things that a neutral atom (the opposite of an ion) won't, and if those things are in your body -- well, that's how you get radiation sickness, cancer, and other not-fun things.

What Radioactivity Is
This one is simple: When an object is radioactive, it is emitting ionizing radiation; in other words, it is radiating something harmful to humans. This radioactivity is measurable with a Geiger counter.

It is worth noting that there is ionizing radiation all around us at a very small level. This is known as background radiation and is so small that it's not worth worrying about. To put it into perspective:
http://xkcd.com/radiation/

  • Doses of ionizing radiation are measured in sieverts (Sv).
  • Absorbing half a sievert all at once will cause radiation poisoning, but this is treatable. 
  • You can absorb up to a full sievert at once and live (but you'll feel terrible).
  • 2 sieverts at once is severe radiation poisoning and is sometimes fatal. 
  • 4 sieverts at once is almost always fatal, and 8 at once is definitely fatal even with treatment. 
  • HOWEVER...  you regularly absorb 10 microsieverts (0.000010 Sv, or 10 uSv) a day without any ill effect whatsoever. 
  • A chest X-ray is 20 uSv. 
  • Eating a banana (because the potassium in them is very mildly radioactive) is a dose of one nano-sievert (0.000000001 Sv, or 1 nSv). 
  • The yearly dose from all the potassium you eat in a year is 390 uSv, which is almost as much as the dose you absorb from a mammogram (400 uSv, or 200 uSv per breast). 
So everything around us is very very very mildly radioactive. The two big things you need to worry about are the magnitude of the dose (see above) and how quickly you absorb it -- half a sievert over the course of a year is going to hurt a lot less than 0.5 Sv all at once. 

Radioactive Half-Life
So what makes some radioactive things more dangerous than others? Why is safe to eat bananas but not radioactive iodine? The answer is a little thing called half-life. To explain what that is, I need to do another "put simply":
  1. Radioactive elements emit ionizing radiation because they are unstable and are decaying into stable forms. Given billions of years, radioactive Uranium decays into non-radioactive lead.
    http://www.pnausa.org/harmony-todd/nuclear-101-radioactive-half-life
  2. It is called "half-life" because it measures how long it takes for a radioactive material to decay to half its value. Therefore, something with a very large half-life lasts longer than something with a short half-life. 
  3. Therefore, it follows that something with a short half-life decays quickly. 
  4. This decay is measured as radioactivity. 
  5. Therefore, something with a short half-life is going to be more radioactive, and put out more damaging radiation. 
In other words, think of radioactive decay as a slap delivered over time. U-238 waits a very long time between slaps; so long, in fact, that you can dodge most of them. Protactinium-234, however, is very much a rapid-fire series -- slapslapslapslapslap -- kind of decay, which makes it much more dangerous. 

What This Means For Preppers
I am greatly simplifying this in order to fit it into a single post, and will go into greater detail in later articles, but this what you ought to know right now:
  • The best way to protect yourself against ionizing radiation is not to be present when it occurs. 
  • If you can't avoid it, put something dense between you and it. The denser the material, the less of it you need, which is why lead is so popular: it is dense and cheap. 
  • However, if you can't get something dense, lots and lots of something cheap will work, provided you have enough of it... for example, water. 
  • 10 feet (300 cm) of water will block neutron radiation (more on that when I talk about ionizing radiation in detail) and alpha and beta particles. It only somewhat blocks gamma rays. 
  • However, gamma rays are easily stopped by materials like granite, concrete, or packed soil. Approximately 8 inches of granite, 12.5 inches of concrete, or 18 inches of packed dirt ought to stop most sources of gamma radiation. 
  • Since both water and soil are easy to come by, constructing radiation shielding for a shelter is pretty easy. If you have an in-ground swimming pool, the best location for your radiation shelter is underneath it. 
  • Protecting yourself without a shelter is more complicated, and will be addressed later. 
If you have any questions, please ask -- I will be happy to answer them in later articles. 

NEXT: Hard vs. Soft Radiation for Dummies

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