X-rays

This is Wilhelm Conrad Röntgen, a German physicist. It’s 1895, and Röntgen doesn’t know yet that he is about to make a discovery that will change the world of medicine and science. Röntgen is in his lab. He's experimenting with “cathode rays” produced inside a little device called a Crookes tube. Suddenly, he notices a faint shimmering on a fluorescent board a few feet away from the Crookes tube.

That's interesting! What could that be? Over the next few days, Röntgen carries out experiments to find out more about the mysterious glow. Röntgen believes that the shimmering must be caused by some kind of unknown rays. The rays are different to the “cathode rays” he has been studying, and they seem to be similar to light!

Because of their mysterious nature, he decides to call them "X-rays". In one of his experiments, Röntgen asks his wife, Anna Bertha, to place her hand between the Crookes tube and a photographic plate. The X-rays pass through Anna Bertha’s hand and create an image of her palm, with dark shadows of her bones and her wedding ring visible. This is the first X-ray image in history! But what are these X-rays?

How come they can pass through solid objects? What can they be used for? Are they safe? Many decades pass before scientists find answers to these questions... Today we know that X-rays, sometimes called Röntgen rays, are a type of electromagnetic radiation similar to light.

Humans can’t see X-rays, because X-ray wavelengths are much shorter than visible light. X-rays also have very high energy. These properties allow X-rays to pass straight through many materials that do not let ordinary light through. The human body, for example. This makes X-rays extremely useful in medicine.

In a process called X-ray imaging, a patient stands between a source of X-rays and a photographic film. Different tissues in the human body absorb different amounts of X-ray radiation, so different tissues cast different shadows on the photographic film. Looking at X-ray images, doctors can see inside your body, and diagnose injuries. There are two types of X-rays: hard X-rays and soft X-rays. Hard X-rays have very short wavelengths, about 100 picometres, and very high energy.

They can penetrate easily through soft tissues, like skin and muscles, but are stopped by bones and teeth, which are harder and denser. In medicine, hard X-rays are often used to diagnose broken bones. Soft X-rays have slightly longer wavelengths, of about 10 nanometres. They also have lower energy, and their penetrating power is smaller than that of hard X-rays. Soft X-rays can pass through skin and muscles as well, but are stopped by denser tissues, like tumours.

This means that they can be used to help detect cancer. Apart from medicine, X-rays can be used for many other purposes, including airport security checks, manufacturing, or quality control of packaged products. Although very useful, X-rays can be dangerous. X-rays are a type of ionising radiation, which can harm living cells. In larger amounts, X-rays can cause serious health issues.

Small doses, such as those used for X-ray imaging in medicine, are generally safe for patients. But people who work with X-rays every day are at risk of being exposed to larger doses. This can be dangerous, and that’s why they need to take special protection measures. Wilhelm Röntgen’s accidental discovery of X-rays turned out to be a great scientific breakthrough. It made him famous and earned him a Nobel Prize in 1901.

But most importantly, it was a huge leap in the development of medicine, and changed the way we see the world.