RADIOACTIVITY
Tuesday, January 26, 2010
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Definition:Radioactivity is the process by which an unstable atomic nucleus spontaneously loses energy by emitting radiations.
Unstable isotopes are usually radioactive. This means they emit radiation to become stable. Unstable atomic nuclei will spontaneously decompose to form nuclei with a higher stability. The decomposition process is called radioactivity. The energy and particles which are released during the decomposition process are called radiation. All known isotopes of elements with atomic numbers higher than lead (82) are known to be radioactive.
The elements exhibiting this phenomenon are called radioactive elements. e.g. radium, thorium, actinium, polonium etc. The isotopes of these elements emitting radiation are called radioisotopes.
Radioactivity was first discovered in 1896 by the 
French scientist Henri Becquerel, while working on phosphorescent materials. He wrapped a photographic plate in black paper and placed various uranium salts on it. Becquerel found that the photographic plate became deeply blackened. Clearly there was a form of radiation that could pass through paper that was causing the plate to become black. These radiations were called Becquerel Rays.
In December 1899, two of Becquerel's colleagues, Marie Curie and Pierre Curie discovered two other radioactive elements, Radium and Polonium. The element radium was two million times more radioactive than uranium. In fact it was Marie Curie, who originally named the phenomenon ‘Radioactivity’. In 1903 both Becquerel and the Curies received the Nobel Prize for Physics.
Unit of Radioactivity:
The curie (Ci) is the old standard unit for measuring the activity of a given radioactive sample. It is equivalent to the activity of 1 gram of radium. It is formally defined by: 1 curie = amount of material that will produce 3.7 x 1010 nuclear decays per second.
The becquerel is the more recent SI unit for radioactive source activity.
1 becquerel = amount of material which will produce 1 nuclear decay per second.
1 curie = 3.7 x 1010 becquerels.
Geiger Muller tube:
Geiger Muller Counter (G.M.Counter) is the instrument which is used to measure the radioactivity.
Types of Radioactivity:
- Natural Radioactivity
- Artificial Radioactivity
When unstable nuclei decompose in nature, the process is referred to as natural radioactivity. When the unstable nuclei are prepared in the laboratory, the decomposition is called induced radioactivity.
posted by Lekshmi @ 1:10 PM,
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