The discovery of the X-ray was met with great excitement around the world, having obvious benefits for medicine as well as opening up an exciting new branch of physics.
The discovery of the X-ray was met with great excitement around the world, having obvious benefits for medicine as well as opening up an exciting new branch of physics.
German physicist Wilhelm Röntgen (1845–1923) discovered X-rays in 1895 while experimenting with electric discharges in glass tubes.
Working in the dark, he noticed a faint glow on a screen nearby – the screen was made of a mineral known to glow when ultraviolet radiation falls on it.
Röntgen realised that the tube was producing invisible rays but he knew they could not be ultraviolet radiation because the tube was covered in thick cardboard.
Even more intriguingly, when he put the screen in a cupboard it continued to glow, but only when the tube was switched on.
Röntgen investigated the effect day and night for weeks, and discovered that his strange rays pass through more materials than light does but are blocked by most dense materials.
Röntgen discovered early on that he could record X-rays and their shadows on photographic paper, and became the first to take X-ray photographs.
He found out that his rays pass through flesh, but not bones, and quickly realised the medical potential of that.
Röntgen did not know what his rays were, so named his discovery after the ‘x’ in algebra that represents an unknown quantity.
Most other scientists at the time called them ‘Röntgen rays’.
Soon after Röntgen published details of his experiment, other physicists realised the mystery rays were another form of electromagnetic radiation.
Physicists knew several already: light, ultraviolet radiation, infrared radiation and radio waves.
The only difference between these various forms of electromagnetic radiation is the frequency – how fast the radiation oscillates as it passes through space.
Ultraviolet radiation had the highest known frequencies, and radio waves the lowest.
Physicists had been waiting for a form of radiation with frequencies higher than ultraviolet radiation – and Röntgen had found it.
The discovery of X-rays heralded the beginning of a new and exciting era of physics.
Within a few months, French chemist Henri Becquerel (1852–1908) discovered another form of electromagnetic radiation with even higher frequencies.
These were gamma rays, produced by ‘radioactive’ materials. Becquerel also found two other forms of radioactive rays that are not electromagnetic radiation.
Physicists were soon using Becquerel’s rays to probe the inner workings of atoms.
And in 1897, English physicist Joseph John Thomson (1856–1940) made the bold suggestion that the stream of particles passing through glass vacuum tubes was carried by ‘corpuscles’ which could be smaller than atoms.
These were later called electrons.
X-rays are still widely used today. Probably their most common use is in medicine, where they are particularly useful for analysing bone defects, but can also detect growths and blockages.
