In this explainer, we will learn how to describe the ways that radioactive material can contaminate the environment.
Contamination is a type of mixing of substances. In contamination, a mixture is produced by adding a substance with particular properties to another substance that has different properties.
For radioactive contamination, the differing property of the substances involved is how radioactive the substances are.
We say that a less radioactive substance is radioactively contaminated when it is mixed with a substance that is more radioactive.
An example of radioactive contamination is shown in the following figure.
We recall that an object is radioactive if it contains atoms that can emit nuclear radiation.
This tells us that any process in which an object containing unstable atoms moves to a place where there are no other objects containing unstable atoms is an example of radioactive contamination.
Let us now look at an example involving radioactive contamination.
Example 1: Defining Radioactive Contamination
Which of the following correctly describes whether or not an object is radioactively contaminated?
- An object is radioactively contaminated if radioactive material has become joined to it.
- An object is radioactively contaminated if it has absorbed nuclear radiation.
It is very important to distinguish between unstable atoms and nuclear radiation. Unstable atoms are the source of nuclear radiation.
An object is radioactive if it contains unstable atoms. This has the same meaning as saying that an object is radioactive if it is a source of nuclear radiation.
Being the source of nuclear radiation does not mean the same thing as having absorbed nuclear radiation. These are opposite meanings.
Radioactive contamination occurs when unstable atoms from a radioactive object are transferred to a different object. This makes the objects that the atoms transfer to a source of nuclear radiation.
It is correct then to say that an object is radioactively contaminated if radioactive material has become joined to it.
When we mention “an object that contains unstable atoms,“ we could be describing many different possible objects.
Any object that contains at least one unstable atom is an example of an object that contains unstable atoms. This could even mean a single unstable atom.
All material objects, whatever their size, are made of atoms. This is true for objects in solid, liquid, or gaseous states. Any such object could be an example of an object that contains unstable atoms.
Let us now look at another example involving radioactive contamination.
Example 2: Describing a Property of Radioactive Objects
Which of the following correctly describes a property of radioactive objects?
- They can be too small to be seen by the human eye.
- They must be too small to be seen by the human eye.
- They must be large enough to be seen by the human eye.
It is very important to distinguish between unstable atoms and radioactive objects.
A radioactive object is any object that contains unstable atoms. Such an object could consist of just a few atoms. Such an object could just as well be an object containing huge numbers of atoms and be larger than a person.
A radioactive object can be too small to be seen by the human eye or can instead be large enough to be seen by the human eye. It is incorrect then to say that a radioactive object must be too small to be seen by the human eye or that it must be large enough to be seen by the human eye.
It is correct to say that a radioactive object can be (but not must be) too small to be seen by the human eye.
Some objects are more easily moved than other objects.
In the example of radioactive contamination shown at the beginning of this explainer, the radioactive liquid can flow and so be poured. The drops of the radioactive liquid can easily diffuse throughout the nonradioactive liquid.
Let us compare this to an example involving two solid objects. This is shown in the following figure.
Just placing the two objects in contact does not make any part of the radioactive solid move to the nonradioactive solid. No radioactive contamination occurs.
Suppose, however, that the radioactive solid is moved while remaining in contact with the nonradioactive solid and so scrapes against it. This is shown in the following figure.
We see that some of the radioactive solid has been deposited as a residue on the nonradioactive object. The nonradioactive solid has now been contaminated by the radioactive solid.
A solid object can be made of a substance that very easily crumbles or flakes.
For such an object, even very gentle contact, such as one from passing air currents, may result in tiny fragments of the object falling from it. These fragments may be so small that passing air currents can lift them and carry them away.
Let us now look at another example involving radioactive contamination.
Example 3: Explaining Why Smaller Radioactive Objects Are More Dangerous Than Larger Ones
Which of the following statements correctly explains why very small radioactive objects are more dangerous than larger radioactive objects?
- Very small objects are more likely to be carried by air or water currents than larger ones.
- Very small objects emit more dangerous types of nuclear radiation than larger ones.
There is no general relationship between the size of a radioactive object and what types of nuclear radiation it can emit. The types of nuclear radiation emitted by an object depend on what elements the unstable atoms in the object are atoms of.
Very small radioactive objects are not more dangerous because of the types of nuclear radiation that they can emit, nor the amount of nuclear radiation that they emit.
The danger of very small radioactive objects is that such objects can more easily contaminate other objects than larger radioactive objects can. This is because contamination requires a contaminant to travel to the object that it contaminates. Very small objects can travel much more easily than larger objects.
We have now seen what radioactive contamination is and some ways in which it can occur.
We will now consider radioactive contamination from radioactive waste products from nuclear reactors.
Radioactive waste from nuclear reactors consists of
- used radioactive fuel,
- objects that have been radioactively contaminated.
It is very important to note that part of the waste is objects that have been radioactively contaminated.
This shows that an object that has been radioactively contaminated may in turn radioactively contaminate other objects.
We recall that a radioactively contaminated object has had unstable atoms transferred to it. This object therefore now contains unstable atoms, and so it is now itself a radioactive object.
Radioactive waste is harmful to living organisms and so must be disposed of to avoid exposing living things to the waste.
The following figure shows part of a radioactive waste storage facility.
A waste storage facility would be built deep underground, in a place far from where any people live.
It is difficult to ensure that the disposed-of waste does not radioactively contaminate the storage facility.
If the storage facility is radioactively contaminated, it then becomes radioactive. The storage facility can then radioactively contaminate its surroundings, including the surrounding air and water.
Contaminated water and air can easily spread great distances, reaching places where many people can be exposed to them.
Nuclear power stations and radioactive waste storage facilities require people to work in them. These workers are at risk of exposure to radioactive contamination.
Protective clothing is used by workers at risk from nuclear radiation. This is shown in the following figure.
The protective clothing prevents radioactive objects from coming into contact with a worker’s skin or being breathed in.
Some radioactive objects emit nuclear radiation that can penetrate the protective clothing however, so the protection given by the clothing is limited.
Let us now look at an example involving radioactive contamination by nuclear waste.
Example 4: Comparing the Dangers due to Radioactive Waste
Which is the greater hazard to most people in the world from a large block of nuclear waste, the nuclear radiation emitted by the block or the radioactive contamination of the block’s surroundings?
- Radioactive contamination of the block’s surroundings
- The nuclear radiation emitted by the block
Suppose that a person stood near to the block of waste. Damage done by the nuclear radiation emitted directly from the block would probably kill this person much sooner than the damage done by the nuclear radiation from radioactive contamination by the block.
The question is not though asking about a single person who happens to be near the block of waste but about most people in the world.
Most people in the world would never be anywhere near the block of waste and would never absorb any nuclear radiation that the block emitted. However, the block of waste could contaminate its surroundings. The surroundings would then become radioactive and spread further contamination around the world. This could affect many people in the world.
Let us now summarize what we learned in this explainer.
- Radioactive contamination is not the absorption of nuclear radiation.
- A less radioactive substance is radioactively contaminated when it is mixed with a substance that is more radioactive.
- Any process in which an object containing unstable atoms moves to a place where there are no other objects containing unstable atoms is an example of radioactive contamination.
- Substances that can more easily mix with other substances can more easily contaminate them.
- Small radioactive objects can more easily act as contaminants than larger objects.
- An object that is radioactively contaminated becomes radioactive and can contaminate other objects.
- Nuclear power stations produce radioactive waste that must be prevented from contaminating the facilities at which it is stored.