In 1896, French scientist Henri Becquerel discovered that uranium salts gave off energy. But he couldn't figure out exactly what was going on.
Marie Curie, a Polish scientist living in France, called these rays "radioactivity". Marie's husband Pierre Curie was a noted chemist. Working together, the Curies discovered two other radioactive elements in 1898: polonium and radium.
By 1903, they worked out what was happening. Certain types of atoms are unstable. They decay over many years and eventually become different and stable elements.
For example, uranium-238 decays into thorium-234 over 4.5 billion years. It then takes about another 341,000 years to turn into a stable element called lead-206.
While the nucleus is changing, invisible radioactive radiation is released. As these rays carry a lot of energy, they can be very useful - or very dangerous.
Positive uses include using radioactive radiation to kill cancer cells. This is called "radiotherapy". It's also used to sterilise medical equipment, detect blood clots, and to treat food.
But radioactive radiation can also kill and mutate body cells, causing internal bleeding, infertility, cancer and many other health problems.
Back in the early 1900s, nobody realised how dangerous radioactive elements are. Marie Curie died as a result of leukaemia caused by the action of radiation.
- Marie Curie was born Marie Skodowska on November 07, 1867 in Warsaw, Poland.
- Marie Curie won the Nobel Prize twice. In 1903, she shared the Nobel Prize for Physics with Henri Becquerel and Pierre Curie. She was also the sole winner of the 1911 Nobel Prize for Chemistry.
- Pierre Curie was killed in a street accident in 1906.
- Irradiation involves the use of radioactive radiation to kill bacteria in food.
- A Geiger Muller counter detects radioactive radiation. A sphygmomanometer measures blood pressure.