What Are X Rays?

Abstract

At the end of 1895, Wilhelm Röntgen (there is a drawing of him in Figure 1.2) was experimenting using a vacuum tube (a glass tube from which the air has been removed) which had a positively-charged plate at one end and a negatively-charged plate at the other. It was well known at that time that in this setup, rays, then called cathode rays, would travel from one plate to the other. It was only later, in 1897, that Joseph John Thomson discovered that these rays were in fact electrons. Röntgen observed that, on hitting the positive plate, the electrons produced some penetrating radiation, which could be detected outside the glass tube by its ability to blacken a photographic film. He called these new rays “X rays”, with the “X” standing for something unknown.

In the end, the public’s health is at stake. An underexposed chest X-ray [picture] cannot reveal pneumonia, and an inaccurate radiation therapy treatment cannot stop the spread of cancer.

Charles W. Pickering 1963–

Summary

X rays are frequently used in medicine and dentistry. They are also widely used in other applications, namely in industrial testing, and in inspection and quality control systems. In solid state physics, the lattice structures of crystals can be determined using X-ray crystallography. Also, in biology, novel X-ray techniques are being used to understand the workings of complicated molecules or even larger molecular structures: X rays were crucial in the discovery of the double-helix structure of the DNA molecule. The X-ray regulations concern X-ray equipment and installations in which electrons are accelerated to energies between 5 keV and 1 MeV. The limits given by the X-ray regulations are defined in a similar way to those in the radiation-protection regulations.