What Are X-rays? - Definition & Uses

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  • 0:01 Marie and Pierre Curie
  • 1:12 What are X-Rays?
  • 2:57 Uses for X-Rays
  • 4:08 X-Rays in Outer Space
  • 4:45 Lesson Summary
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Lesson Transcript
Instructor: Maria Howard

Maria is a teacher and a learning specialist and has master's degrees in literature and education.

This lesson describes X-rays and their many uses, from looking at broken bones to analyzing the rocks on Mars. Learn how X-rays are part of the larger electromagnetic spectrum, which ranges from radio waves to powerful gamma rays.

Marie and Pierre Curie

The 1903 winners of the Nobel Prize in Physics, Marie and Pierre Curie, were dedicated scientists who studied and advanced the use of X-rays. Marie Curie, born Marie Sklodowska, immigrated to Paris from Poland at 24 years old to continue her study of math and physics. There, she met and married Pierre Curie, a respected physicist, and they soon began working together, testing different elements to see which gave off radiation, or waves of electromagnetic energy.

Marie and Pierre Curie
Image of Marie and Pierre Curie

We know now that radiation can be very dangerous stuff, but little was known back then. Marie and Pierre Curie and their daughter Irene, who also worked with them in their laboratory, were exposed to such extremely high levels of radiation every day that they all suffered from health problems because of it. Marie and Irene administered thousands of X-rays on French battlefields during World War I, with nothing to protect them but the clothes on their backs. Both mother and daughter eventually died of illnesses caused by their repeated exposure. Even now, the Curies' work papers (and even their cookbook) contain such dangerous levels of radioactivity, you have to sign a waiver before you are allowed to handle them.

What Are X-Rays?

X-rays are powerful waves of electromagnetic energy. Waves, like those found in the ocean, are the movement of energy. When you clap your hands, energy, in this case sound, begins at a source. The sound travels through the air as waves until it reaches your eardrums and registers as sound. Waves that travel through a physical medium, like air and water, are called mechanical waves.

Electromagnetic (EM) waves don't require a physical medium to travel across, so they can exist on both Earth and in space, where there is no air for even sound waves to travel through. EM waves are organized along a spectrum according to the distance between each wave and the frequency of waves per second, measured in hertz (Hz).

The waves with the lowest frequencies and the greatest distances between waves give off relatively low amounts of energy. Radio waves, for example, have the lowest frequencies of the different categories of the waves on the electromagnetic spectrum, while gamma rays, created by nuclear explosions, have the highest frequencies.

Diagram of the Electromagnetic Spectrum
Diagram of electromagnetic spectrum

X-rays are the band of electromagnetic waves just before gamma rays on the EM spectrum. They are at the far end and, along with gamma rays and some ultraviolet rays, are shown as damaging to DNA. As we know from the injuries sustained by Pierre, Marie, and their daughter Irene during their X-ray experiments, X-rays are very powerful in their own right. At about one quintillion waves per second - that's 1,000,000,000,000,000,000 Hz - we think of them as 'rays' of energy rather than waves.

Uses for X-Rays

When they were first discovered over 100 years ago in 1895 by Wilhelm Conrad Roentgen, X-rays were used in much the same way that we use them now - to see the bones inside our bodies. Roentgen would often demonstrate X-rays by taking an image of the bones in his wife's hand. Bones (and other objects) are denser than skin. They absorb enough radiation to create shadows on X-ray film and show us when bones are broken or if little Timmy has indeed swallowed a penny.

X-Ray of a Knee
X-ray image of a knee

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