Radiation

Historian Alex Wellerstein explains how people are exposed to radiation, and the kinds of radiation that can be harmful.

Narrator: Historian Alex Wellerstein talks about how radiation is all around us in various forms.

Alex Wellerstein: You get a lot of radiation from eating a banana. I mean, not a lot by health standards, but just a detectable amount because there’s potassium in bananas. Potassium’s a little bit radioactive.

You actually get some radiation if you sleep next to somebody at night, because they are slightly radioactive and you are slightly radioactive. And it actually is a measurable amount of radiation difference.

What we worry about for radiation hazards, one is a very large amount of radiation all at once. So an atomic bomb produces a huge burst of neutrons and gamma radiation. Inside of a nuclear reactor is a lot of radiation. These are very, very powerful amounts of radiation. And that’s the kind of radiation that if you go too near to it, you can die within either seconds, or if you’re exposed to a burst of it, you can die within weeks. It’s a very unpleasant way to die.

The other thing that we worry about with radiation are long-lived weakly radioactive substances that can be uptaken by the body. So there’s an inverse relationship to how powerful radiation is and how long it sticks around.

So some atoms, like the ones that you get from a nuclear fission, these unstable pieces, are extremely radioactive. They’re the kind of thing that will kill you dead within seconds. But they only stick around for a couple of hours at the most, because they’re so radioactive that they spit out all their energy at once and they don’t have anything left.

And then there’s stuff that’s around for on the order of thousands of years or hundreds of years or even tens of years. If those substances get inside of you, then they can sit inside of you and radiate and radiate and radiate.

Physicist and teacher Jay Shelton provides an overview of ionizing radiation.

Narrator: Physicist and teacher Jay Shelton explains that radiation is all around us, and he also explains how ionizing radiation can remove electrons from an atom or molecule.

Jay Shelton: There is natural background radiation everywhere. It’s coming down from the cosmos, it’s coming from our own bodies, which have carbon-14 and potassium-40, totally natural. Other things in us, comes from the air, from radon, comes from the ground. So it’s all around us at low levels.

Ionizing radiation clearly does have health effects, because it ionizes atoms and molecules, which means it kicks electrons out. Which means that it disrupts bonds, because the bonds between atoms to make molecules are all about what the electrons are doing.

So it can change the chemistry. It can change the chemicals in your body. Therefore, of course, there’s a potential health impact.

Physicist and teacher Jay Shelton describes three forms of ionizing radiation – alpha, beta, gamma – and the health risks posed by each type.

Narrator: Jay Shelton explains that ionizing radiation comes in three main forms. And to help us remember, he has nicknames to describe the three types: Alpha Elephant, Beta Bunny, and Gamma Sammy Sidewinder.

Jay Shelton: Alpha particles are like elephants, in the sense that they are by far the heaviest of those three if you look at the mass. They also are the slowest. An alpha particle is a nucleus of a helium-4 atom, two protons and two neutrons. That is pretty massive in this context.

Beta radiation is one electron going fast. Way, way, way less massive, by factors of thousands. And they go faster.

Then Gamma Sammy Sidewinder is gamma radiation which has no rest mass, travels at light speed. You can’t go any faster.

They are very different in what they do, too. Alpha radiation is slow. Has a very hard time getting through other atoms.

Beta is in-between. It’s an electron. It’s a little smaller, and it can maybe go a few millimeters into our bodies coming from the outside.

Gamma radiation is very penetrating and can go completely through you. Sometimes it goes completely through you and does nothing to you, because it didn’t deposit any of its energy.

They are very different in terms of what they do and what kinds of protective measurements are necessary. Alpha radiation coming at you from the outside, no worry. There is alpha radiation and beta and gamma coming from everything. Everything is naturally radioactive.

Alpha is a concern if you eat or breathe the materials which are going to send out that radiation, because then you don’t have a protective layer of dead skin. Beta radiation also is mostly of concern when consumed or breathed. Gamma is a concern anywhere, because it does penetrate.

Physicist and teacher Jay Shelton describes how ionizing radiation impacts the body.

Narrator: Jay Shelton can explain why it takes a great deal of exposure to ionizing radiation to pose a health risk, and how the body responds.

Jay Shelton: There are other things that ionizing radiation can do, but I think the biggest concern is cancer. It results when any one of these kinds of radiation scrambles the chemistry of DNA in a very particular way, and it doesn’t get repaired, which it usually does. It can lead to cells having the wrong instructions.

If you want to scare somebody, what you do is you tell them that we get hit by ionizing radiation on the order of 10 or 15,000 times every second. Each one of those has enough energy to perhaps, on average, ionize thousands, tens of thousands of molecules in your body.

If you add up the total number of busted bonds that we get, we might get a billion broken chemicals in our body every second of our entire lives. If you don’t get quantitative about that, you just sort of get scared and think, “My God, I must be dead!” Well, we’re not, and so the question is well, why not?

Although a billion is big, maybe it is tiny compared to what is there. That is part of the answer. Part of the answer is, a lot of the damage is totally inconsequential. Part of the answer is that a lot of the damage that could be gets repaired. The bottom line is, it is not really that scary.

Physicist and teacher Jay Shelton explains how a Geiger counter measures ionizing radiation. Many thanks to Grant W. Trent for providing the Atomic Heritage Foundation with video of a Geiger counter in use.

Narrator: A Geiger counter is an instrument that measures ionizing radiation. Jay Shelton explains how it works.

Jay Shelton: A Geiger counter has inside of it a Geiger tube, and a Geiger counter only detects ionizing radiation. That ionizing radiation knocks electrons off of atoms and molecules that it happens to encounter. The detector has to be sensitive to that.

Inside of every Geiger counter, there is one or more Geiger tubes. The tube has a wire going down the middle and a metal can around the outside and kind of a special mixture of gases.

So ionizing radiation comes along. It has to get through the metal, and it will ionize some of the gas. There is a huge voltage difference between the wire and the can, which means if there’s any charge in the air, the electrons get pulled down to the wire and the positive ions get pushed out into the can. It is a very, very strong electric field.

If you create a bunch of free electrons, which is what ionizing radiation does, it knocks them out. The electron gets pulled very strongly towards the central wire. Now, of course, that ionizing radiation may ionize a few atoms, but here’s the real key.

You get amplification, and you get a cascade. You get one electron, which is now loose from its atom, can start moving in very fast towards the wire. It is so fast that it itself becomes ionizing radiation, and when it bumps into another air molecule, it will knock an electron or two off of it. Now you have two.

They now will get accelerated, and they bump into another and you get more and more. You get a cascade of electrons being created by this process, that pulse of electrons hitting the wire. That makes a tick, makes a light blink, makes a counter go up by one. It directly is detecting ions created by ionizing radiation, which of course is what we need.