The discovery of X-Rays

Online exhibition looking at how electricity in a medical capacity has developed from the Antiquities through to the early twentieth century. Quack treatments are examined alongside studies of anatomy and x-rays.

Postcard commemorating the birth of Wilhelm Rontgen

At the end of the nineteenth century, physicists suspected that most startling discoveries had been made and the future of the discipline lay in more precise measurements of known phenomena.  They were wrong: in a short space of time, the discovery of X-rays, uranium rays and the electron transformed the discipline.  All three, however, were based on careful observation and established technology.

The discovery of X-rays by Röntgen in 1895 was a combination of luck and methodical exploration. Röntgen had been studying the discharge of electricity in gases, using a vacuum tube.  Up to this point, scientists had concentrated on what was happening inside the tube, which was highly interesting.  If an electrical current was passed through the tube and the gases in the tubes were gradually evacuated using a vacuum pump, patterns of light emerged.  

Eventually, although the entire tube was dark, the cathode appeared to be emitting some form of ray.  As Röntgen repeated some of the experiments which had been carried out on these rays, with a tube shielded by black card, he noticed that a piece of fluorescent paper nearby was affected.  This could not be the effect of cathode rays, so it must be an entirely new form of radiation.

When asked what he had thought when he saw this,Röntgen responded, 'I did not think, I investigated'.  He tried moving the paper and testing the properties of the rays, which he called 'X-rays' because of their unknown nature.  Amazingly, one of things he tested in those first few weeks was passing the rays through the human hand (while not knowing whether the rays were harmful!) and took the first X-ray photograph of his wife's hand, showing her bone structure and wedding ring.  Right from the beginning, the medical and anatomical possibilities of this discovery were apparent.

The American X ray Journal June 1897

When Röntgen published his results, everyone wanted to try the new rays.  Soon they were used to locate a bullet in someone's hand and a glass splinter which was embedded in a finger.  The first photographs showing tubercular infection of the bones was published.  Besides finding foreign bodies and identifying disease, doctors could also use X-rays to examine the anatomy of normal, living subjects.  They could also investigate the effects of congenital deformities and diseases such as arthritis on the bones.

X-rays came to be used more and more as a diagnostic tool, especially as ways of photographing soft tissues, such as the digestive tract, were discovered.  It was also found that these rays could have harmful effects and efforts were made to protect those operating the machines with lead-lined gloves and aprons.  Eventually, with the development of the computer, three-dimensional X-rays were made possible with Sir Godfrey Hounsfield's invention of the CT scanner.

But what were these X-rays?  After much experimentation, they were found to be a high-energy form of electromagnetic radiation.  When a free electron hits an atom, it can cause an electron orbiting the nucleus to sheer off.  One of the electrons orbiting at a higher level will then drop down, emitting its excess energy in the form of a photon.  The energy level of the photon determines the type of electromagnetic radiation: from radio waves (low) to gamma rays (very high).  

In the early tubes, X-rays were produced by the action of electrons on the glass wall of the tube.  In later equipment, a hot cathode was used, which fires off high-speed electrons which then strike the tungsten anode.  The tube is shielded with a small window to allow the X-rays to escape in a tight beam.

X ray of Silvanus P Thompson's hand taken April 1896
An x ray of a hand, the first X-ray photograph taken in India January 1897


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