How Do X-Rays Work?

Did you know x-rays were discovered entirely by accident?
Trevor English

Chances are you've had an X-ray at some point in your life, but did you know that this life-saving technology was actually invented by accident? German physicist Wilhelm Roentgen discovered the technology while he was doing experiments with electron beams and gas discharge tubes – you know, like everyone does...

Initial discovery

When performing these tests, he noticed that a fluorescent screen in his lab started to glow green while the electron beams were running. This wasn't surprising in its own right, but Roentgen's screen was shielded by heavy cardboard, which he thought would block the radiation.

The interesting part of this discovery was that the initial aspect of Roentgen's discovery was simply the existence of some kind of penetrating radiation, but in trying to figure out what was happening, he actually put his hand in between the screen and the electron beam. This created an image of the bones inside of his hand on the screen, revealing X-ray's perfect use immediately after their discovery.

This double discovery marked arguably one of the most important medical advances in all of human history. It gave professionals the ability to see ailments inside the human body without invasive surgery. It even allowed them to see soft tissues with slight modifications.

No one questions that X-rays are important to modern medicine, but most people don't have a great idea of what is actually happening when you get one.

How X-rays work

You can think of X-rays as light rays. Both are electromagnetic energy carried in waves by photons. The one major difference between these types of rays is the energy level, or wavelength, of the rays.

We have the ability to sense light rays in the wavelengths of visible light, but shorter or longer wavelengths fall outside of our visible spectrum. X-rays are higher energy waves, and radio waves are longer lower energy waves.


X-rays are produced by the movement of electrons within atoms. The specific energy level of a given X-ray is depended upon how far the electron dropped between orbitals in an atom.

When any given photon collides with another atom, the atom can absorb the photon's energy and boost an electron to a greater level. In this case, the energy of the photon has to match the energy difference between the two electrons. If this doesn't occur, then the photon can't shift between orbitals.

How Do X-Rays Work?
Patient being examined with a fluoroscope. Source: Wikimedia/National Cancer Institute

This functionality means that as photons from X-rays pass through your body, each tissue's atoms absorb or react to photons differently.

The soft tissues in your body are composed of smaller atoms, so they don't absorb X-rays well due to the photons' high energy. On the other hand, the calcium atoms of bones are much larger, so they do absorb the X-ray photons and thus result in a different view on the X-ray image.

X-ray machines

Inside of X-ray machines, there is an electrode pair, an anode, and a cathode, inside of a vacuum tube, usually made of glass. The cathode is usually a heated filament, and the anode is a flat disc made of tungsten. As the cathode is headed up, electrons spurt out of the filament and find their way to the anode.

The voltage difference between the anode and the cathode is very high, which allows the electrons to travel through the air with a high velocity. As these electrons travel through the tube at such a high pace and hit the tungsten atoms of the anode, it knocks loose electrons in the lower orbitals of the atoms. As electrons fall from higher orbitals to these lower energy levels, the extra energy is released as a photon. Since this drop is large, it releases a high-energy photon or an X-ray.

This is how normal X-rays are produced and function, but in cases where soft tissue, like human organs, need to be examined, then contrast media needs to be added. Contrast media are liquids that absorb X-rays and collect in soft tissues. To examine blood vessels, doctors will inject this media into veins. Oftentimes in these cases of soft tissue viewing, doctors will also use Fluoroscopes to see the image in real-time and can even capture videos using these devices.


To collect the actual image from an extra, doctors use a film or sensor on the other side of the patient. These films work nearly identical to normal photographic film, and the sensors are particularly sensitive to X-rays.

Through all of this imaging, doctors can deduce a wide array of important medical data from X-rays.

Even with the significance of X-rays, they can still be dangerous in high-doses as they are a form of ionizing radiation. This means that when an X-ray hits an atom, it can actually knock electrons off to form an ion or an electrically charged atom. The free electrons then collide with other atoms to create more ions. Ions can cause unnatural chemical reactions within the body resulting in mutations in a patient's DNA. This mutation can then become cancerous.

It's this reason that doctors sparingly use X-rays, or at least use them only when absolutely necessary. In low doses, X-rays are nothing to be afraid of and can be a life-saving medical technology in the modern era.

Alternatives to X-rays

If you don't want to get an X-ray because you are worried about the potentially harmful effects, there are few solutions. In many cases, ultrasounds may work to examine any ailments under the skin, but not always.

Ultrasound also referred to as sonography, is essentially your best option when trying to avoid x-rays. These imaging techniques work by sending sound-waves with higher than audible frequencies through your body. Scanned bodies are affected in no way from these sound waves, which is a major benefit. 

The ultrasound machine then listens for changes in the sound wave as well as monitors various rates of return to create a live image of what's underneath. 

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