Above: Image © Michael Müller-Hillebrand, Wikimedia Commons

If you were able to pick between two super powers, which would you choose... X-ray vision or the ability to fly? Sure, it would be cool to fly anywhere and anytime you wanted. But just imagine what you could do with X-ray vision nudge-nudge, wink-wink>.

Did You Know? X-rays were discovered accidentally. The 'X' was originally used to denote the mathematical symbol for unknown.

When X-rays were first discovered, people were amazed that they could be used to see inside our bodies. Today, of course, we tend to take X-rays for granted. If you've ever needed surgery, broken a bone, had a tooth filled or flew somewhere, you've likely been exposed to X-rays.

How X-rays work, actually, is very simple. But it does require some understanding of the behaviour of electrons in atoms.

Electromagnetic Radiation

X-rays are similar to visible light rays. Both consist of energy in the form of electric and magnetic fields (electromagnetic radiation) and both travel as waves at a speed of about 300,000 km/s. But what makes them different are their respective wavelengths; the distance between adjacent wave crests.

Did You Know? Radio waves, microwaves, ultraviolet rays and gamma rays are other examples of electromagnetic radiation.

Visible light has a wavelength of between 380 and 760 nanometres (one nm = one billionth of a metre) whereas the wavelength of X-rays is only 0.01 to 10 nanometres! With a much shorter wavelength, X-rays have way more energy. This is because the frequency (or the rate at which a wave passes a given point) is greater.

X-Ray Photons

The energy in electromagnetic radiation is carried in particles called photons. X-ray photons are created in vacuum tubes by bombarding a tungsten anode with electrons. This causes an electron in the tungsten atom to be knocked loose from a low energy space (orbital). As a result, an electron from a higher energy orbital immediately falls to the lower level, releasing its extra energy in the form of a photon. The amount of energy in a photon depends on how far an electron has dropped between orbitals — the higher the drop, the more the energy is produced.

Did You Know? Medical and dental X-rays are low intensity, so their hazards are minimal.

The energy level will also determine how a photon behaves when it collides with another atom. If the energy of the photon matches the energy difference between two electron positions in that atom, its energy will be absorbed. How? By boosting an atom's electron to a higher level.

How X-Rays Work

The reason X-rays work so well in distinguishing body parts is because different body parts are made up of atoms of different sizes. For example, bones or tumors contain larger atoms. Because the energy differences between orbitals closely match those of high energy level of X-ray photons, these structures absorb X-ray photons much better than the smaller atoms found in body tissues (i.e. fat, muscle, etc).

Did You Know? Lead strongly absorbs X-rays because it contains a high number of electrons (82) with a wide range of orbitals.

For X-rays to be useful though, we use photographic film to be able to see how they behave in the body. What are produced are negative images where areas that are exposed to more light are darker than areas exposed to less light. As a consequence, our bones, since they absorb the X-rays, show up as white whereas our other body parts are seen as different shades of grey or black.

In closing...

At one time, X-ray glasses were very popular as a novelty item. One attraction was the claim that they allowed you to see through clothes. For anyone who knew how X-rays worked, this was utter nonsense. In fact, how the glasses themselves worked wasn't even remotely based on X-ray technology. If you don't know the "secret" behind X-ray glasses, click here.

Learn More!

Stan Megraw

Stan is a writer/researcher, a PhD graduate of McGill University and was a member of the CurioCity team for several years. As a kid he dreamed of playing hockey in the NHL then becoming an astronaut with NASA. Instead, he ended up as an environmental research scientist. In his spare time Stan enjoys working on DIY projects, cooking and exploring his Irish roots.


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