What is radiation?

Radiation is energy that travels as a wave or particle. Some types of radiation can harm you. These types are called ionizing radiation. When this radiation is given off by substances such as uranium as they decay, it's called radioactivity.

About half of the ionizing radiation we're exposed to comes from nature. It's in rock, soil, and the atmosphere. The other half comes from man-made sources. These include medical tests and treatments and nuclear power plants.

How much radiation is dangerous?

There is always a risk of harm to cells or tissue when you get any amount of ionizing radiation. Over time, exposure may cause cancer and other health problems. But in most cases, the risk of getting cancer from being exposed to small amounts of radiation is small.

The chance of getting cancer varies from person to person. It depends on:

• The source and amount of radiation exposure.
• The number of times you are exposed.
• Your age when you are exposed.

In general, the younger you are when you are exposed to radiation, the greater the risk of cancer. For example:

• Someone who has had many CT scans starting at a young age is more likely to get cancer later in life than someone who hasn't had any or as many of these tests. As a rule, CT scans use more radiation than other X-ray tests.
• A child who was treated with radiation for cancer is more likely to get another cancer later in life.
• A person who has been exposed to large amounts of radiation from a nuclear accident is more likely to get cancer than someone who has not been exposed.

Exposure to small amounts of radiation doesn't cause any symptoms. But getting large amounts all at once may cause radiation sickness and death.

How do different sources of radiation compare?

Some sources give off larger amounts of radiation than others. For example, when you go through a full-body airport scanner, you get very small amounts. But if you live near the site of a nuclear accident, you're exposed to large amounts.

You may be exposed to more radiation than other people if you:

• Live at high altitude.
• Have certain medical tests or treatments. This includes X-rays, CT scans, and radiation treatment for cancer.
• Are exposed to radon gas in your home.

It may be helpful to compare some common sources of radiation to a standard dose from a chest X-ray. A chest X-ray gives off very small amounts of radiation.

For example:

• You would need to go through a full-body airport scanner about 1,000 times to get the same amount of radiation that you would get from 1 chest X-ray.
• A 10-hour plane flight is about the same exposure as 1 chest X-ray.
• One mammogram test is about the same as 5 chest X-rays.
• Living at a high altitude (such as in Calgary) for a year is about the same as having 4 chest X-rays.
• One CT scan is about the same as 200 chest X-rays.

What can you do to protect yourself?

You can't avoid radiation that occurs around you in nature. But there are some things you can do to reduce how much you get from man-made sources.

• You may be concerned about the risk of getting cancer from a CT scan. If so, talk to your doctor about how much radiation this test may give you. Make sure that you need the test. Ask if another test, such as an ultrasound or an MRI, can be done instead. In some cases, the benefits of having a CT scan outweigh the small risk of getting cancer.
• You may have concerns about getting radiation from a full-body airport scanner. If so, ask if you can get a pat-down instead. (But the amount of radiation you get from one of these scanners is very low.)
• If you are exposed to radiation from a nuclear accident:
  • Wait for instructions from public health and emergency officials. They can tell you what to do. Depending on the kind of accident, they may tell you to shelter in place or simply to stay indoors. You don't need to leave your community unless local authorities tell you to.
  • Don't take potassium iodide (KI) tablets unless local authorities tell you to and your doctor says that it's okay. These can harm you if you don't take them the right way. They help protect your thyroid gland from the harm done by radioactive iodine. This can be released as a result of a nuclear accident. They don't protect you from any other radioactive substances.