Lesson Video: Sources of Radiation Science

In this video, we will learn how to identify different sources of nuclear radiation.

08:53

Video Transcript

In this video, we will learn how to identify different sources of nuclear radiation. As we’ll see, some of these sources are natural and some are artificial made by humans.

As far as natural sources of radiation, believe it or not, the Earth itself is a source. Much of the Earth is made of rock. When we take samples from the outer layer of this rock, called the crust, we find very, very small amounts of radioactive material. Only about 10 out of every one million atoms in the Earth’s crust is made of such a material. The radioactive elements we might find in the crust include thorium and uranium.

As we think about the surface of the Earth, we know that most of it is covered by water. The water in Earth’s oceans and seas passes through rock in the crust and picks up some radioactive material. We can say then that rock, soil, and water are all natural sources of radiation. We can even go a bit further. Because what grows in soil and through water is food that humans eat, even some of our food is a radiation source. A person on Earth is exposed to all of these natural sources. The radiation levels from these sources is quite low. It’s not enough to be harmful to humans.

Along with sources of radiation from the Earth, there are also sources from space. One of these sources is the Sun. The Sun and other active stars are like big nuclear reactors. Nuclear radiation from the Sun travels through space and reaches Earth. Most of this radiation is blocked by Earth’s atmosphere. Going outside Earth’s atmosphere on missions to space requires special protection from this radiation. Any radiation coming from outside Earth’s atmosphere is called cosmic radiation.

We see then that natural sources of radiation really are all around us. Shielded as we are by Earth’s atmosphere, this background radiation is not hazardous to us. The reason for this, as we’ve seen, is that radioactive material is so rare on Earth. We could say that we find it everywhere but just barely. It’s possible, though, to purify samples of rock and soil so the radioactive sources are more abundant. This gives us a highly concentrated piece of radioactive material. Because a sample this concentrated doesn’t naturally occur, we call it artificial.

There are two main uses for artificial sources of radiation. One is in nuclear power plants. These plants generate electricity from nuclear energy. A second use of artificial sources of radiation is nuclear weapons. When a nuclear weapon detonates, it spreads radioactive sources into the environment. Currents of air carry radioactive material all throughout the Earth. Radioactive material is also released onto the ground. Nuclear weapons, then, are a source of radiation.

Nuclear power plants, on the other hand, when they operate properly, are not a significant source of radiation. Under normal operation, the reactor core shields the radioactive sources in the reactor so that they and the radiation they give off is contained. However, in the case of an accident, nuclear radiation may no longer be properly contained. In an explosion, it’s even possible for the radioactive source to enter the environment. So a nuclear power plant can be a source of radiation when there’s an accident. These are quite rare, but they are possible.

A nuclear weapon, on the other hand, is always a source of radiation whenever it’s detonated. Detonating a nuclear weapon releases radiation and also the sources of that radiation, the radioactive materials themselves.

Let’s look now at a few examples about sources of radiation.

Is nuclear radiation emitted by Earth?

Planet Earth is made largely of rocks. When we analyze these rocks, we find very small amounts of nuclear material. More common radioactive elements on Earth include uranium, radium, and radon. Even though it’s in very small amounts, too small to be dangerous to humans, nuclear radiation is emitted by the Earth.

Let’s look now at another question.

Does any nuclear radiation emitted by some objects beyond Earth reach Earth?

When we think of objects beyond Earth, that would be any object in space. Nuclear radiation is created in stars, and that includes our Sun. Just as light from the sun reaches Earth, so does nuclear radiation it gives off. Most radiation from space, called cosmic radiation, is blocked by Earth’s atmosphere. Nonetheless, some does make it through and reaches Earth’s surface. In answer to this question, then, we can say, yes, nuclear radiation emitted by some objects beyond Earth does reach Earth.

Let’s look now at a question about an artificial source of radiation.

When an accident occurs at a nuclear reactor, which of the following is the main health risk for people living far away from the nuclear reactor? (A) Nuclear radiation escaping from the reactor. (B) Sources of nuclear radiation escaping from the reactor.

Our two answer options might seem similar, but there’s an important difference between them. Say that we have a source of nuclear radiation. This could be a chunk of radioactive material like uranium or plutonium. This source gives off radiation. The source and the radiation are two separate things. In this example, we’re imagining an accident at a nuclear reactor. So let’s say that here is our reactor that has had an accident, say, by a hole being opened up in the reactor. We want to know what is the main health risk for people living far away.

During normal operation, a nuclear reactor contains radioactive material. The reactor is designed to shield this material from spreading as well as block the radiation it gives off. If a hole was opened in the wall of the reactor, two different things could escape: first, nuclear radiation, what is given off by the radiation source. It’s also possible, though, that the source of the radiation itself could be released from the reactor.

For people living far away from the reactor, the radiation by itself escaping would not pose a significant health risk. That’s because it has to travel such a long distance that by the time it reached these people, it would not be very harmful. However, if the sources of radiation themselves were projected out of the reactor, these could then give off radiation at a much closer distance to the people concerned. So it’s the sources escaping from the reactor that is more dangerous than the radiation itself. We choose answer option (B).

Let’s look now at one last example.

Which of the following correctly describes the relation between nuclear waste and nuclear radiation? (A) Nuclear waste is a source of nuclear radiation. (B) Nuclear waste is a type of nuclear radiation.

So we’re trying to decide whether nuclear waste is a source or a type of nuclear radiation. Let’s start by considering just what nuclear waste is. A nuclear reactor is designed to safely contain sources of nuclear radiation. When these sources become depleted, they are removed from the reactor and put into thick containers. These depleted sources of radiation are called nuclear waste. The reason nuclear waste needs to be contained is it’s still a source of radiation. If nuclear waste was a type of radiation, it would radiate out and disappear quickly. But because it is a source constantly giving off nuclear radiation, it must be shielded from the environment. We choose answer option (A).

Let’s now finish this lesson by reviewing a few key points. In this video, we saw that sources of nuclear radiation naturally exist on Earth and in space. Nuclear radiation from space is called cosmic radiation. And lastly, we learned about artificial sources of nuclear radiation. These include nuclear reactors that have experienced an accident and nuclear weapons. This is a summary of sources of radiation.

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