Science & Technology in Action

Introduction
Although X-rays have many uses people generally associate them with their use in medical diagnostics. X-rays can pass through soft body tissues relatively easily but are stopped to some extent by denser tissues such as bone. For many years after their discovery in the 1870s, scientists investigated their properties but were largely unaware of the dangers associated with them.

As with all sources of ionising radiation, their use results in a radiation dose and an increased risk of cancer later in life. Small doses from diagnostic X-rays carry a small risk, large doses or repeated use carries a higher risk.

Discovery
The German physicist Wilhelm Röntgen is usually credited with the discovery of X-rays in 1895, but others were aware of their existence about twenty years earlier but had not studied them to the same extent. Röntgen took an X-ray photograph of his wife’s hand to demonstrate their possible medical use.

What are X-rays?
X-rays are electromagnetic waves having the same nature as visible light, ultra violet, infrared, radio waves and microwaves, etc. These types of electromagnetic radiation differ in their wavelength; those with shorter wavelength have greater energy. The energy of photons of ultraviolet and X-rays is sufficient to break chemical bonds and so these radiations are said to be ionising. Gamma rays are like high energy X-rays and are mainly produced in nuclear interactions such as radioactive decay. Cosmic rays, which are believed to come from exploding stars (supernovae), have even greater energy than gamma rays; they have been found to consist mainly of high energy protons and are largely blocked by the atmosphere. They generate gamma rays when they collide with molecules in the atmosphere or indeed in living things.

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