RADIOACTIVITY
Most atoms are stable. They remain the same through time. Others are unstable – they are likely to break up. As they do so they give off some of their particles or energy in the form of rays. These particles or rays are known as radioactivity. Examples of chemical elements with radioactive atoms include uranium, plutonium and radium. As atoms give out particles or rays they change into the atoms of simpler elements. For example, uranium changes into lead. This change is called radioactive decay. It happens at different speeds or rates for different radioactive elements. The time taken for half of a number of atoms to decay is known as the half-life of that element. Radioactivity can be dangerous since it harms living things. But under controlled conditions it is very useful in medicine and scientific research.
The name “radioactivity” was invented by Polish-born scientist Marie Curie (1867-1934). She studied various rocks and minerals from the Earth and gave the name to the invisible rays or particles that some of them gave off, which affected photographic paper and various electrical equipment. In particular Marie worked with the substance pitchblende, a raw material used to obtain the metal uranium. Pitchblende, gave off more radioactivity than expected from uranium alone. Marie purified the substances which gave off this extra radiation and so discovered two new elements, polonium and radium.
How do we know the age of mummies from Ancient Egypt? By measuring the tiny amounts of radioactive substances they contain. This is known as radiocarbon dating.
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