Radiation or radioactivity is one of the scariest words in the English language.
While radiation can indeed be very dangerous, most people don’t really understand how it works and it is often treated as magic death cooties which leads to unwarranted fear.
Learn more about radiation, how it works, and where it’s found in nature, on this episode of Everything Everywhere Daily.
We need to start any discussion of radiation with what it is.
The textbook definition says that “radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium”.
This actually includes a large number of things including light, radiant heat, and radio waves.
However, when we hear people talk about radiation, they are usually not talking about light bulbs and radio antennas. That is because there are two different types of radiation: ionizing and non-ionizing radiation.
Visible light, radio waves, and things we deal with on a daily basis are all non-ionizing radiation. The stuff that deals with nuclear power, bombs, or medical procedures is all classified under ionizing radiation.
Ionizing radiation just means that the energy emitted in the particle or photon is high enough to remove an electron on an atom or to break a molecular bond.
For the rest of the show, when I refer to radiation I’ll be referring to ionizing radiation because that is really the focus of this episode.
Ionizing radiation comes in three forms: Alpha particles, Beta Particles, and Gamma Rays.
All three of these types of radiation are due to a process called radioactive decay.
So if you remember back in science class, all atomic nuclei are made up of protons and neutrons. Protons have a positive charge and neutrons have a neutral charge. The number of protons determines what element it is.
For example, iron will always have 26 protons. If it had anything else, it wouldn’t be iron.
However, iron or any other element can have different numbers of neutrons. 92% of all iron in nature has 30 neutrons. There are also some that have 28, 29, 31, or 32. All these different numbers are called isotopes, and in the case of iron, those 5 isotopes make up over 99.9% of all the iron you can find. These isotopes are also stable isotopes.
A stable isotope, just as the name implies, means that it’s happy just as it is.
However, some isotopes of some elements are unstable. That means that can only stay in that state for so long, and it’s going to change. When they change, that’s radioactive decay.
It’s important to know the difference between the three. Alpha, beta, and gamma.
Alpha decay is when a nucleus spits out a helium atom. Two protons and two neutrons will be expelled from the atom, turning the atom into a new element.
All of the helium we have on Earth comes from the process of alpha decay. Radioactive elements deep in the Earth undergo alpha decay, spit out a helium atom, and the helium gets trapped under the Earth. Helium on the surface will quickly go to the top of the atmosphere and disappear.
Of the three types, alpha radiation has the lowest energy and can be the safest type of radiation. An alpha particle can be blocked by almost anything. A piece of paper, your clothes, or even your dead skin cells will block an alpha particle.
The danger in alpha particles comes if you should ingest them. If an alpha emitter were to get into your lungs, it could cause a great deal of damage. That is why radon can be so dangerous. You might remember a Russian critic by the name of Alexander Litvinenko who was poisoned with polonium 210 back in 2006.
Polonium is a very radioactive alpha emitter with an extremely short half-life. Litvinenko was poisoned with it and died, he is believed to be the first victim of polonium 210 poisoning.
The second type of radioactive decay is beta decay. This happens when a neutron spits out an electron, or a proton spits out a positron.
Beta particles have more energy than alpha particles. A piece of paper or some clothing isn’t going to stop beta radiation. You will need something like a thin metal sheet to stop it. A beta particle is about 100x as penetrating as an alpha particle.
Strontium-90 is a common beta emitter and it is often used for medical purposes. Doctors will target beta emissions on to a tumor in an attempt to kill it.
The final type of radiation is gamma radiation. This is really nasty stuff.
Unlike alpha or beta radiation which is a physical particle ejected from an atom, gamma radiation is a high-energy photon.
Because it is a photon and has no mass, and because it has so much energy, blocking gamma rays is quite difficult. It requires thick concrete or lead shielding.
If you are even required to swallow something in a medical procedure so they can track it through your body, it will probably be a very weak gamma emitter, just because the rays are more likely to just travel right through you.
Of the three types of radiation, alpha emitters are the safest to have outside your body, and the worst to have inside your body. Likewise, gamma and beta emitters are the safest to have inside your body and the most dangerous outside your body.
What most people don’t realize, is that they are exposed to radiation every second of their lives. In fact, you, listening to this podcast right now, are yourself radioactive.
Natural radiation comes from two primary sources. The first is cosmic rays. Cosmic rays are high energy particles that come from space. They might come from the sun, or they might come from outside our galaxy. They are whizzing around all the time, entering our atmosphere.
So, unless you are listening to this in a deep mine, you are being bombarded by cosmic rays. Moreover, the high up in altitude you are, the more cosmic rays you are exposed to.
Someone living in Denver will get as much background radiation due to altitude as someone living in Chernobyl….and that is really more a statement on how low the levels are in Chernobyl than how high they are in Denver.
Likewise, flying is one of the things which is responsible for the largest exposure to radiation which more people will receive. A single transatlantic flight will give you more radiation exposure than 5 chest x-rays.
If you look at a list of jobs with the highest exposure to radiation, you’ll see an airline pilot right next to a nuclear medical technician.
The other major source of natural radiation is background radiation from the Earth. Elements like Uranium are natural and found in rocks in the soil, often in trace amounts. Some unstable isotopes, like carbon 14 are produced in the upper atmosphere by cosmic rays.
Living in a house made of stone as opposed to one of wood will increase the amount of radiation you are exposed to. Likewise, as odd as it may seem, a coal-fired power plant will cause more radiation exposure than a nuclear power plant. The reason is that there can be trace amounts of naturally occurring radioactive materials in coal, which when burned, will travel in the atmosphere and be inhaled into the lungs. Everything in a nuclear power plant, however, is shielded and never exposed to the outside.
This natural radioactive decay is what is also responsible for most of the heat in the interior of the Earth. Geothermal energy, is really just nuclear power, using the Earth’s mantle and core as the reactor.
How is it that you are radioactive? This mostly comes from Potassium-40, a naturally occurring isotope that makes up 0.012% of all potassium. Because you have potassium in your body, some small amount of that will be radioactive and hence you are. One of the most radioactive foods you can eat is a banana because they have so much potassium.
All of these things which I’ve mentioned are true, but they are very low levels of radiation.
As I mentioned before, ionizing radiation can destroy molecular bonds, like in our cells or in DNA. However, life evolved on the planet in such an environment, so our bodies can repair a certain amount of cellular and DNA damage. When it gets too much, that is when we run into problems.
How radioactive something is can be measured in half-life.
Half-life is a pretty easy concept. Because radioactive decay involves an atom changing into something else, the half-life is just the length of time it takes for a unit of it to become half the amount. If you have a gram of uranium 238, the half-life would be the amount of time it takes until you only have half a gram left.
In the case of uranium 238, that would take 4.5 billion years.
The thing with half-lives is that the shorter the half-life, the more dangerous it is. In the example I gave above of polonium 210, it has a half-life of 138 days. It is extremely radioactive. Uranium 238, you can easily hold it in your hand.
So what is the deal with nuclear power and nuclear bombs?
Those could be entire episodes on their own, and perhaps they will someday, but to oversimply it, I’ll just talk about the thing which most bombs and reactors have in common: uranium 235.
Natural uranium comes in two forms, uranium 238 which makes up 99.3% of all the uranium, and uranium 235 which makes up the other 0.7%.
To make a nuclear reactor, you need uranium 235, the rare type, which has a half-life of 700 million years. The problem is, you need to separate it from the uranium 238 which is really hard to do. Separating two different elements is pretty easy. You can do that chemically. Separating two different isotopes is really hard to do, because they are basically the same thing, except for a small difference in weight.
When U 235 is hit with a neutron, the atom splits and it sends out more neutrons, which split more atoms and send out more neutrons, et Cetra.
If you have a whole lot of U235, then you get an uncontrolled reaction and that is how you make a bomb. You would need over 90-95% U235 to create weapons-grade uranium. That is very hard and expensive to do.
To make fuel for a nuclear reactor, you want U235, but not so much. The fuel in a nuclear reactor only has 3-5% U235. That is why a nuclear reactor literally cannot blow up like a bomb.
If a half-life means that there is less something over time, that means that in the past there must have been more of it. Because of the different half-lives of U238 and U235, it is possible that in the deep past on Earth there was enough U235 to cause a natural nuclear reaction?
The answer, believe it or not, is yes. They’ve found evidence in the nation of Gabon that 2 billion years ago, a natural nuclear fission reaction had to have existed given the isotopes they now find there. It would have created a lot of heat, not too dissimilar from a volcano.
You might have heard of something called Plutonium. Plutonium is not a naturally occurring element. It is only found as a product of man-made nuclear reactions. It is really nasty stuff and one of the deadliest substances on the planet.
However, it has its uses. The primary use for plutonium is as fuel for deep space missions.
Whenever we send a probe to Jupiter or beyond, it will always be fueled by plutonium 238. Solar panels just don’t work when you are that far away from the sun, so you need something else.
Plutonium 238 has a half-life of 88 years, so it’s pretty radioactive. It produces a lot of heat. A block of it could sit in one place and be hot for years and years, which is perfect for powering a spacecraft.
For example, on the New Horizons mission to Pluto, it was powered by a radioisotope thermoelectric generator (RTG). This takes the heat from plutonium and converts it directly to electricity. They are a very safe and simple power source, but it isn’t very efficient. Only 3-7% of the heat is converted to electricity, but when you are billions of miles away and have years to get there, you have plenty of time to charge up your batteries.
If you’ve ever wondered how we can still keep in touch with the Voyager spacecraft, over 43 years after they were launched, it is due to plutonium 238.
Not long ago, NASA was worried about the supply of plutonium 238 because they were running out and couldn’t fuel deep space probes. Since then, they’ve found a new way to manufacture it, so we have plenty for the future.
Radiation is something that definitely needs to be respected. It can do a great deal of damage. However, it is also something that is natural at certain levels that we all live with every day of our lives.
So, the next time you heard something about radiation on the news, instead of thinking of it as magical death cooties, take a more nuanced approach. Compare it to the background radiation you receive every day, or the amount you might receive in a plane flight, to get a better appreciation for what is really happening.