The discovery of X-rays, and what we can learn from it (Patreon)

[This is a transcript of the video.]

This is the amazing story of the discovery of X-rays, the trouble that followed, and what we can learn from it.

It’s November and the year is 1885. Wilhem Conrad Röntgen is in his laboratory in Wuerzburg, Germany. For the past weeks he’s been studying the new cathode ray tubes from his colleague Phillip Lenard.

Cathode ray tubes are glass tubes with a negative and a positive electric pole, called the cathode and anode. To the tube you can attach a vacuum pump. When the voltage is turned on and high enough, and the vacuum is good enough, the tube begins to glow with a color that depends on the gas inside of it. It’s the same principle that was later used for neon lamps.

They didn’t know it at the time, but what happens is that electrons are kicked out from the negatively charged cathode plate and travel into the direction of the positively charged anode. When they hit some of the atoms of the gas in the tube, the atoms start to emit light. For air it’s usually green, which comes from oxygen and nitrogen, that’s the same color you also see in the aurora. No it’s not aliens.

The electrons don’t all go to the anode, some of them fly past. But they don’t go through glass. The innovation from Roentgen’s colleague Lenard had been that he put an aluminum coating on one side of the tube. When thin enough, this would let these cathode rays through while still maintaining the vacuum inside the tube.

This was the first time cathode rays could be studied outside of the glass tube. And this is what Roentgen is interested in as he is working in his lab on this November day. He knows that cathode rays travel at most two centimeters in air and can be blocked by as little as a sheet of paper because he can measure the current they create. He also knows that the rays make some fluorescent materials shine, and this is what Roentgen is working with today.

He wants to see the beam that comes out of the Lenard tube with a plate that is covered by fluorescent material. The glow is very faint, so he closes the windows to see it better. But even with the windows closed there is still the glow from the tube. So he puts a cardboard box onto the tube to block the light.

And then he notices that the fluorescent plate glows even though it isn’t in the direction of the cathode beam.

Now remember that Roentgen knows that the cathode beam can easily be blocked by glass and paper. So why is the plate glowing? The cathode beam couldn’t have gotten there. He turns off the tube. The fluorescence disappears. He turns it back on. It reappears. He holds the fluorescent plate closer to the tube, it becomes brighter. He moves it away and finds the glow is still clearly visible meters away from the tube. Even though the cathode rays are going in a different direction and only travel two centimeters in air. Something odd is going on.

He puts different materials between the tube and the fluorescent plate. The thicker the material in between, the less the plate shines. Eventually he puts his own hand in between. He sees his own bones.

Roentgen concludes there are some kind of unknown rays coming from the tube that are absorbed more by the bones than by the rest of the tissue. He briefly considers calling them twitter rays, but then settles on X-rays. Just checking if you’re listening.

Roentgen didn’t tell anyone about his discovery for weeks, he just experimented around. I can just imagine how exciting this must have been. He was the first person ever to see this. It was all his own to discover. This is every scientist’s dream.

He quickly figured out that some standard photographic plates were reacting to the new X-rays and that allowed him to take images. One of the first images he took was of his wife’s hand. According to some anecdotes she reacted by saying “I have seen my own death,” presumably referring to the image and not to her husband. She refused to ever enter his laboratory again.  

It wasn’t until January 1896, that Roentgen gave a lecture about his discovery which was later translated and published in Nature magazine. By this time he had figured out that the higher the density of a material, the better it blocked the X-rays. The best material to block them that he found was lead.

The scientific community was baffled. Lord Kelvin thought it was a hoax. The confusion of other scientists was hilariously captured in this 1940 clip from General Electrics in which they promote an X-ray device.

Roentgen was awarded a Nobel prize in 1901 for his discovery. In the following years work from William Bragg and Fritz van Laue showed that X-rays were electromagnetic radiation just like visible light but with shorter wavelengths and that were emitted in the cathode ray tube along with the visible light.

It had become clear to Roentgen quickly that one of the major applications of these new X-rays would be medical. He deliberately did not patent the idea to make it easier for other people to use them. And indeed, X-ray imaging with beams from cathode tubes was rapidly adopted by the medical profession.

But it also became popular for other purposes. For example, you could have your feet X-rayed inside shoes to make sure the fit was perfect. This is a real shoe box from the 1960s where they still advertise this service.

For some time after the discovery of X-rays people put the word x-ray on everything from pills to polish. It’s kind of like they today put the word “quantum” on everything.

As time passed it became apparent that X-rays weren’t all that healthy. The first to notice were people operating X-ray machines who suffered burns on their hands. The burns weren’t just superficial, they went deep into the tissue. So they began using lead shielding.

But that wasn’t it. People irradiated on their head lost hair. Some began developing cancer. By the 1940s and 50s scientists began to push for safety regulations.

Gradually X-ray machines became less of a health hazard. That was partly because of better shielding and better focussing of the beam but also because photographic plates became increasingly sensitive so that less radiation was needed to take an image. If you get a small X-ray today, of your teeth or hand, the radiation dose is comparable to a few days of natural background radiation. Unless you get a big X-ray like a full body scan or so it’s usually nothing to worry much about.

So this is the story of the discovery of X-rays and I think there’s a lesson in it. X-rays have been dramatically helpful for the medical profession and many people’s lives were improved or even saved by the possibility to look inside the body. But the new technology was adopted without much understanding about how it worked, and that lack of understanding caused illness and death, both of patients and people working with the machines.

I believe we should keep this in mind when we are dealing with Artificial Intelligence today. It’s new technology that can bring dramatic benefits. But it could be dangerous, and it makes sense to study it before throwing it upon mankind.

This video comes with a quiz that lets you check how much you remember.