Looking through the body

Physicist Dirk Lützenkirchen-Hecht on the 100th anniversary of the death of Wilhelm Conrad Röntgen

Exactly 100 years ago, on February 10, 1923, one of the most famous sons of Bergisches Land died in Munich, whose discovery of X-rays revolutionized medical diagnostics: Wilhelm Conrad Röntgen. How did he discover the X-rays named after him?

Lützenkirchen-Hecht: Actually, it was a coincidence. Shortly before, Johann Hittorf and others had experimented with electron beams, and Röntgen had picked up on that. He was very interested in many things and also did experiments. What one did at that time, one held into the electron beam, for example, a crosshair, and on the luminous screen behind it one could see that of the rays hitting the crosshair, nothing more arrived behind it on the screen. Nothing then shone at these points. Röntgen then went one step further and wrapped the entire apparatus in black cardboard and then placed a photo plate or a fluorescent screen behind this cardboard again. And then he saw that there was a trace on it, from which he concluded that there must be something else. And that's how he discovered X-rays. So the electrons are slowed down by the glass or the photographic plate and the electron energy is converted into what we now call X-ray light.

A mistake led him to leave school without a degree. What had happened?

Lützenkirchen-Hecht: That's a bit curious. His mother was Dutch, and he traveled around a lot when he was young. The things that are practiced today, at least before the Corona crisis, that you go abroad and have an exchange, Röntgen did that when he was a child and a teenager. He was in Apeldoorn and went to school in Utrecht. A caricature of his class teacher circulated there and he was accused of being the author. No apologies helped, he was expelled from school and therefore did not graduate.

Röntgen was a stand-up guy. Nevertheless, he studied in Switzerland via courses and an entrance examination and graduated as a mechanical engineer in 1868. How did he get into physics?

Lützenkirchen-Hecht: Röntgen had a wide range of interests. He came to mechanical engineering through a friend who took him to the Swiss Federal Institute of Technology in Zurich (ETH Zurich). He was interested in mechanical engineering because he was fascinated by mechanics and construction. Already in Holland, he had also taken courses in biology, mathematics, physics and chemistry in a kind of guest study, but without being officially admitted as a student. Therefore, I suppose, his really very broad interest in various subjects can be explained. So he came back to physics through a friend, August Kundt, and did his doctorate.

Even before his most important discovery, Röntgen, who had taught at the University of Würzburg since 1888 and turned down many calls to other universities, was highly respected among experts. His first test subject was his wife, whom he exposed to radiation. What did he X-ray on her?

Lützenkirchen-Hecht: The hand! This is one of the most famous pictures and was also a title page in the annals of physics. You can see the wedding ring there, from today's technology with very poor resolution, but revolutionary at that time. One could see through the hand. Röntgen then immediately experimented a lot, held different materials in the beam and saw that the ring absorbed much more of the radiation than the bone tissue or the skin. He was very fast and very far for his time. He always said the research he does should have broad utility. He did not apply for patents on his inventions, but published everything freely and also immediately passed on the drafts he had made for the publications to his colleagues throughout Europe, thus also ensuring very rapid dissemination. There was to be widespread benefit from this important discovery.

Röntgen was the first Nobel Prize winner in physics. When did he receive the award?

Lützenkirchen-Hecht: 1901, so the discovery was in December 1895 and the publication followed in 1896. From the very beginning, Röntgen recognized the possibilities of this technique. It was a revolutionary and a really important discovery for mankind. All of a sudden there was the possibility to look through the body. Unimagined possibilities arose for medicine, also for technology and archaeology. It was possible to X-ray welds, masonry or mummies without causing damage. The Nobel Foundation was established in 1900, and the direct award to Wilhelm Conrad Röntgen a year later documents the great significance of his discovery.

In 1923, Röntgen, who was suffering from colon cancer, was a patient of Ferdinand Sauerbruch, another famous son of the Bergisches Land, who complained to his patient that Röntgen's discovery was leading many doctors to stop examining accurately. Do you know what he replied to that?

Lützenkirchen-Hecht: "Where there is a lot of X-ray light, there must also be X-ray shadow."

That's fitting. Today, after all, we know much more than we used to. Back then, many scientists exposed themselves to radiation doses that were far too high. Electron beams also caused many researchers to contract laryngeal cancer, because they were always looking into their equipment. The ease with which bone fractures could then be diagnosed may have tempted doctors at the time to "wildly" x-ray everything, and this is probably what Sauerbruch was alluding to.

After his death, he decreed in his will that all his scientific records were to be destroyed, which his friends did. Therefore, only a few documents of his still exist. Why do you think he did that?

Lützenkirchen-Hecht: Röntgen was a very critical contemporary. Before he published anything, he double- and triple-checked it. By destroying his documents after his death, he certainly also wanted to prevent his reputation from being damaged and other scientists from perhaps using his designs in a way that was not in his interest. He was very critical of himself. For us today, of course, this is also a pity, because historically interested people have no possibility to access his manuscripts in order to perhaps learn what he thought and how he proceeded. There would certainly be many things that could still be discovered.

In Lennep, there is still the German X-ray Museum. Have you ever been inside?

Lützenkirchen-Hecht: Yes, several times. It's a great thing. I'm thrilled every time, because they're constantly working on the exhibitions. There are themes for which new exhibitions are being designed again. A visit is always interesting and worthwhile for children, adults and scientists alike.

Uwe Blass

Apl. Prof. Dr. Dirk Lützenkirchen-Hecht is a member of the Institute Condensed Matter - X-ray Physics in the Faculty of Mathematics and Natural Sciences at Bergische Universität.