Lesson Explainer: Sources of Radiation Science

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

Nuclear radiation occurs naturally. Unstable atoms that can emit nuclear radiation exist throughout the universe. We can say that there are naturally occurring sources of nuclear radiation.

It is also possible to deliberately make unstable atoms more likely to decay. This is only possible for some isotopes of some elements. When nuclear radiation is emitted by atoms that have been deliberately made more likely to decay, this is called artificial nuclear radiation.

Let us first consider natural nuclear radiation.

One source of natural nuclear radiation is the planet on which we live. Unstable atoms naturally occur in some of the rocks of which planet Earth is formed.

Unstable atoms present in rocks are also present in water. This is because water naturally passes through rocks when it falls as rain. Small pieces of rock are carried by this water.

Living organisms take water into their bodies, and so some living organisms contain unstable atoms.

We see then that natural nuclear radiation from Earth can be present in many objects. The amount of nuclear radiation from these objects is usually not enough to be dangerous to people. In some places in the world, however, there are much more radioactive rocks than other places. In these places, the natural nuclear radiation from the ground is much greater.

The other source of natural nuclear radiation is objects beyond Earth, in outer space. The Sun emits a very great amount of nuclear radiation. All stars do this. Astronauts that travel into space are exposed to a great amount of nuclear radiation. This nuclear radiation is called cosmic radiation.

Much of the nuclear radiation from beyond Earth does not penetrate the atmosphere of Earth. People on Earth are at much less risk of harm from cosmic radiation than astronauts. Some cosmic radiation does reach the surface of Earth, however.

We can see then that there is no way to entirely avoid natural nuclear radiation. The only way to avoid cosmic radiation would be to travel deep under Earth’s surface. Doing this would increase exposure to the natural radiation from rocks. This is shown in the following figure.

Natural nuclear radiation from Earth is represented by pink arrows. Cosmic radiation is represented by white arrows.

Let us now look at an example concerning natural nuclear radiation.

Example 1: Deciding Whether Earth Emits Nuclear Radiation

Is nuclear radiation emitted by Earth?


Earth contains radioactive rocks. The unstable atoms in these rocks and from these rocks emit nuclear radiation. Yes, Earth emits nuclear radiation.

Let us now look at another example.

Example 2: Deciding Whether Nuclear Radiation from Space Affects Earth

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


Nuclear radiation from beyond Earth must travel through Earth’s atmosphere to reach Earth. Most of the nuclear radiation is absorbed in the atmosphere but some of it does reach the surface. Yes, some nuclear radiation from space reaches Earth.

Let us now consider artificial nuclear radiation.

The amount of naturally occurring nuclear radiation is much greater than the amount of artificial nuclear radiation produced.

Artificial nuclear radiation has three sources:

  • explosions of nuclear weapons,
  • accidents at nuclear power stations,
  • normal operation of nuclear power stations.

It might seem that because these sources produce much less nuclear radiation than natural sources, they are less harmful.

It is important though to understand these sources of artificial nuclear radiation are also sources of radioactive material.

Let us first consider nuclear weapons. A nuclear weapon test is shown in the following figure.

The BAKER test of Operation Crossroads

When a nuclear weapon explodes, some of the material that weapon is made of is scattered by the explosion. This material is radioactive.

When nuclear weapon tests were done that involved explosions above ground, the radioactive material released traveled all across the world on wind currents. Most of the radioactive material traveled much shorter distances than this, though, and fell to the ground not very far from the place where the weapon exploded.

Underground nuclear weapon tests did not spread radioactive material as widely as explosions in the air. Radioactive material in the ground did eventually become released by natural processes, however, such as water passing through the ground and carrying small pieces of radioactive material with it.

Now let us consider accidents at nuclear power stations.

Accidents at nuclear power stations are not the same as nuclear weapon explosions. Radioactive gases and radioactive materials in water have been accidentally released due to malfunctions in nuclear power stations.

In some accidents, enough radioactive material was released that any people living near the power station where the accident occurred could have been made seriously, or even fatally, ill by the nuclear radiation from the radioactive material released.

Now let us consider the normal operation of nuclear power stations.

Almost no nuclear radiation is released from a nuclear power station that operates normally. It is, however, normal for a nuclear power station to produce radioactive waste. This waste can be disposed of by storing it safely. When radioactive waste is stored safely, the only people at risk from nuclear radiation from the waste are the workers involved in taking the waste from the power station to a waste-storage facility.

Let us now look at an example concerning nuclear waste.

Example 3: Describing Nuclear Waste

Which of the following correctly describes the relation between nuclear waste and nuclear radiation?

  1. Nuclear waste is a source of nuclear radiation.
  2. Nuclear waste is a type of nuclear radiation.


Nuclear waste is something that is radioactive, so it emits nuclear radiation. This means that nuclear waste is a source of nuclear radiation, not a type of nuclear radiation.

Let us look at example concerning accidents at nuclear power stations.

Example 4: Identifying the Dangers due to Accidents at Nuclear Reactors

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?

  1. Sources of nuclear radiation escaping from the reactor
  2. Nuclear radiation escaping from the reactor


Most of the nuclear radiation released from a nuclear reactor during an accident travels only a short distance before it is absorbed. People living far away are not at risk from this radiation.

An accident can, however, involve releasing radioactive material that can be carried in the air or in flowing water. This material consists of sources of nuclear radiation. These sources can travel great distances and so can be a danger to people far from the reactor.

Let us now summarize what has been learned in this explainer.

Key Points

  • Natural nuclear radiation is emitted from sources in Earth.
  • Natural nuclear radiation is emitted from sources in space. This is called cosmic radiation. Some cosmic radiation reaches the surface of Earth.
  • Most nuclear radiation people are exposed to is natural.
  • Artificial nuclear radiation is emitted by nuclear weapons and nuclear power stations.

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