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Background Radiation: Definition, Causes & Examples

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  • 0:00 What Is Background Radiation?
  • 1:23 Measuring Radiation
  • 1:44 Sources of Radiation
  • 4:35 Lesson Summary
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Lesson Transcript
Instructor: Erin Tigro
This lesson will define background radiation, explain how it is measured, discuss some of the sources and examples of background radiation, and briefly consider the risk to humans. A short quiz will follow.

What Is Background Radiation?

Right now, you are being flooded with radiation. Lots of radiation. While this might sound like something that could cause a person to run screaming, it really is nothing to worry about.

Radiation is a word that has a lot of meanings. The light from a light bulb is a form of radiation, and some of the heat emanating from a bowl of soup is also radiation. But the term background radiation usually refers to a specific type of radiation: ionizing radiation.

Ionizing radiation is radiation with high enough energy to cause ionization in the objects in comes into contact with. That is, this kind of radiation can cause changes in individual atoms. If it hits a human being, ionizing radiation can cause the electrons to leave the atoms in cells. This kind of ionization has the potential to be harmful, causing cancer and even birth defects.

Just like less harmful forms of radiation, we are constantly being hit with ionizing radiation in a constant background dose. Much of it comes from radioactive substances that surround us in the air, in the ground, and in space above us. But we even create our own, in medical instruments like CT scanners and through nuclear meltdowns and warfare. The term background radiation refers to the ionizing radiation that we are constantly exposed to, no matter what we do.

Measuring Radiation

Radiation is usually measured in units called milli-sieverts (mSv). Anything up to 50 mSv per year is considered safe, though the greater your exposure to ionizing radiation, the more likely it is to hurt you. A dose of 1000 mSv is associated with a 5.5% risk of eventually developing cancer.

Sources of Radiation

But where exactly does all this radiation come from? Believe it or not, all around you. The air you breath, the food you eat, even from space and from the earth itself. Let's take a closer look at some of these sources.

The Air You Breathe

There is no greater illustration of how impossible it is to avoid background radiation than the air itself. You are almost constantly breathing. The air we breathe is the largest source of background radiation for most humans, giving the average person a dose of 1.26 mSv per year. Americans get about 2.28 mSv.

The Food You Eat

The food you eat and water you drink also contain radioactive materials that add to our constant background radiation. Food and water give the average person a dose of 0.29 mSv per year.

The Earth Itself

Even the ground beneath you has scattered radioactive materials, though the dose you get varies hugely by location. In parts of Finland, you might receive as big a dose as 7 mSv per year, but the average worldwide dose of earth-based radiation is around 0.48 mSv, although it's only 0.21 in the USA.

Cosmic Rays

And just like we receive radiation from below, we receive it from above. Cosmic ionizing radiation from space constantly bombards us. Most of this radiation is pushed aside by the earth's magnetic field or interacts with matter in the atmosphere before reaching us, but we still receive an average of 0.39 mSv per year from cosmic rays (0.33 in the United States). Astronauts in space lack the full protection that the earth provides, and can receive 100 mSv or more in a single mission. NASA rules limit astronauts to 1000 mSv over their careers. There is also cosmic microwave background radiation leftover from the Big Bang, but microwaves are not high energy enough to cause ionization.

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