Published on October 12th, 2012 | by Sara Callori1
A look at the Nobel Prize in Physics: From the spectacular to the forgotten – William Roengten, 1901
If I asked most people to name a discovery or a physicist that won a Nobel Prize in physics, they would probably mention Einstein (although forget his prize was for the photoelectric effect), Marie Curie, maybe graphene because it’s fresh in people’s minds, and maybe murmur something about quantum mechanics or the structure of the atoms. But over the last hundred years, the Nobel Prize committee has recognized a lot of great (and some forgettable) physics and physicists. In this series of articles, we are going to try to take a look at as many as we can.
Since this is the beginning of this series, the first Nobel Prize seems like a good place to start. Awarded in 1901, the inaugural prize went to a discovery that eventually made its way from the laboratory into common usage all over the world.
The first Nobel Prize in Physics was awarded to Wilhelm Roentgen for “extraordinary services he has rendered by the discovery of the remarkable rays subsequently named after him”. If “Roentgen Rays” don’t seem familiar, that’s because they are much more familiarly known as X-rays.
At the time of his discovery in 1895, Roentgen was a physicist at several universities in German and was studying light emission from cathode ray tubes, which are vacuum tubes where a beam of electrons (the eponymous cathode ray) flows between electrodes placed at opposite ends of the tube. Roentgen was observing what happens when the cathode ray was allowed to escape the tube through a small aluminum window covered by a piece of cardboard to make the tube light-tight.
Roentgen noticed that although the tube was sealed with respect to light, when a cathode ray was produced within the tube, a nearby barium platinocyanide screen would produce fluorescence. He further tested this set up with a different cathode ray tube and again found that the barium screen produced fluorescence in a dark room, even when it wasn’t directly next to the tube.
Thinking he might have found a new type of ray, Roentgen spent the next two weeks systematically studying his new discovery, which he termed “X-rays” because their nature was still quite unknown. He investigated their penetrative power, observing that they went through wood and books. When he placed a piece of lead in the beam by hand (Note to aspiring physicists: Don’t try this at home!), he was able to see an image of his skeleton on the barium screen. From there, his wife served as his next subject and Roentgen used his X-rays to take the first X-ray radiogram (which is also known as a Roentgenogram).
Only two months after his discovery, Roentgen published his results is a paper titled “On a New Kind of Rays.” (You can read a translation here.) In this paper, he had two hypotheses for a description of X-rays. The first was that it was a new kind of ultra-violet ray, one previously unobserved. The second was that X-rays were actually a type of longitudinal wave. Light was well know by then to be a transverse wave, so he thought that the difference in wave type was the explanation for why X-rays had such, well, weird properties. Roentgen felt that because these properties were so unlike the observed properties of light, that the first explanation just couldn’t be possible. But once physics was able to catch up, the description of X-rays actually matched that of a new type of ultra-violet ray. That is because X-rays are actually electromagnetic waves with wavelengths of 0.1 to 10 nm. Considering the electromagnetic spectrum, of which visible light is a small fraction, this means that, like light, X-rays are transverse waves, just much more energetic than visible light and ultra-violet rays.
Roentgen eventually published two more papers on x-rays , becoming the first scientist to thoroughly study this new type of radiation. His X-rays became widely used not only throughout medicine as a diagnostic tool but through many fields of science. Within the field of physics, scientists realized that because the wavelength of X-rays is on the atomic scale, they could be used to obtain the structure of materials. This discovery and experiments based on it lead to other Nobel Prizes not just in physics but in chemistry and medicine as well. X-ray fluorescence made by different objects can give scientists information about a material’s composition. And X-rays are even used in the art world in analyzing the paints and colors in some of history’s most famous works of art. So it’s safe to say that, in terms of Nobel Prizes, Roentgen’s inaugural win is one of the prizes with the mode wide-reaching legacy.