Fundamentals of Nuclear Science: Half-lives and The Weather Girls.

So it has come to my attention that a surprising number of people don’t actually know what half-lives are and what they describe. And as you know, when there is something about nuclear science that the general population does not understand, they immediately assume the worst possible thing.

At it’s most fundamental a radioactive half-life is; The amount of time it takes for half of an amount of one pure radioactive element to decay to another element on average. This is about as far as general knowledge extends. But notice that I didn’t say it “becomes stable”. As I’ve mentioned before, there are only really 4 common types of radiation, and only 2 of those really happen in normal radioactive decay (alpha and beta). So since most radioactive elements eventually decay to lead as their final stable element it usually takes several decay events to get from say Uranium 235 down to Lead 207.

about this many in fact!

Now I know this might look more complicated than expected but it’s simple to read once you remember that an atom can only do one thing at once. So those atoms in there that have multiple paths can only take one or the other. This is actually hugely important, no matter how obvious it might sound and is actually one of the things that get glossed over a lot whenever nuclear safety and half-lives get talked about in the public sphere. It means that radiation isn’t a constant thing, it is, in fact, many small, single things.

So radiation is not a continuous thing, and each bit of radiation only happens on a step down the decay chain towards a stable final element. This is what people miss about half lives when they are working themselves into a lather about nuclear waste that will be “dangerous” for “tens of thousands of years”. A sample of radioactive material gets less radioactive with every bit of radiation that it releases!

Fundamentally every radioactive atom is like a drunk guy balanced on a pole, he’s going to fall sooner or later it’s just a question of time. Now if you have a few groups of 1 or 2 of them then it’s hard to predict when they are going to fall because there are too many possible reasons for them to fall and not enough guys to see all the possible methods. However, if you had a few groups of 1000 guys then it would be much easier to predict because you would be able to watch one group after another and get an idea for how hard it is to balance on the pole. Some elements are fairly stable like Uranium 238 or Thorium 232 which have half-lives in the hundreds of millions to tens of billions of years. And many elements are very very unstable with half-lives in terms of microseconds. But every “guy” can only fall once.

So at the risk of beating this metaphor to death, which do you think would be the safer field of drunk guys balancing on poles to be standing under? One where it takes a long time for them all to fall or another where it wouldn’t be out of place to be humming “Let the Bodies Hit the Floor” or “It’s Raining Men” to yourself as you dash around trying not to get flattened?

“It’s Raining Men,” and “Let the Bodies Hit the Floor,” are about the same event, but wildly different perspectives. from r/Showerthoughts

Thank you, r/Showerthoughts. But I need to get back on point. Long half-life elements release their radiation very slowly. In the case of some elements like Thorium, it can take longer than the current age of the universe for half of a given amount to decay. So when someone tells you that something that something is going to be dangerous for hundreds of thousands of years they either have a fundamental misunderstanding and think that radioactive materials just emit a constant amount of radiation for this magical period of time called a half-life, or they are trying to scare you because they think you don’t know enough to counter their argument.

Now about short half-life materials. Yes, they can be super fucking dangerous. But are they? Not really because, as healthcare professionals can tell you, The Danger is in the Dose. If you can get enough of a short half-life isotope together in one place yes, it could be very dangerous to your health. When you have something that has a half-life measured in hours or less though, there is a slight problem doing that since most of your sample will decay away while you are trying to make more of it. Their own instability is your greatest protection against the threat of exposure.

So we can, in fact, work with these materials with no risk of danger to people or the environment. And here’s a good part about these materials… They disappear quickly. In some cases within months, and in other within hours. So while they might be absolutely terrifying while they exist, they don’t exist for long. Radiation basically cleans itself up if we put it someplace safe for a little while. And even if it takes a few hundred years to reach the levels we define as Safe, it will be barely any more dangerous for most of that time.

For example, say you define 1% of the initial radiation of a specific sample as the safe level. That means it will take about 6 half-lives to get to that level. (50%>25%>12.5%>6.25%>3.125%>1.0625%) If you are paying attention half of that time it is less than 10%. Radiation is not magic, it follows rules and behaves accordingly. And if we all know those rules and respect them, then no one will ever have to fear it uncontrollably again.

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