The phenomenon of radioactivity was discovered by Henry Becquerel in 1896. It may be defined as the phenomenon of spontaneous emission of high energy radiations (alpha rays, beta rays and gamma rays) from certain heavy elements by disintegration of their heavy nuclei. And the substances which emit such radiations are called radioactive substances. Examples of various radioactive substances are: uranium, radium, plutonium, thorium, polonium etc.
When a radioactive substance emits alpha particles or beta particles they change to other elements. For example, when an atom of U-238 disintegrates to emit an alpha particle, it changes to thorium element.
92U238 90Th234 + 2He4
Uranium Thorium Alpha particle
In the same manner, carbon-14 can change into nitrogen by emitting a beta particle.
6C14 7N14 + -1e0
Carbon Nitrogen Beta particle
Types of Radioactivity
The radioactivity is of two types:
- Natural radioactivity and
- Artificial radioactivity
When a substance emits high energy radiations on its own, it is said to possess natural radioactivity. For example, radioactive isotope of uranium (U-238) is very unstable in nature and emits radioactive radiations on it own.
Up to 1919, it was thought that the process of radioactivity can take place only naturally, i.e. heavy nuclei of elements can disintegrate on their own to emit radioactive rays. But in 1919, Rutherford discovered that certain elements which are otherwise stable can be made to disintegrate by bombarding them with suitable particles. In his experiment Rutherford bombarded the stable nuclei of nitrogen-14 with fast moving alpha particles which resulted in formation of new element (O-17) and protons after their disintegration.
7N14 + 2He4 8O17 + 1H1
Nitrogen Alpha particle Oxygen Proton
This phenomenon of disintegration of otherwise stable nuclei by bombarding them with suitable particles is called artificial radioactivity. And the particles used for bombarding the nuclei are called projectiles. These days various types of particles are used as projectiles to carry out artificial radioactivity. These are:
- Alpha particles
- Neutrons and
Test Your Understanding and Answer These Questions:
- Who discovered radioactivity?
- What is definition of radioactivity?
- What are types of radioactivity?
- What is natural radioactivity?
- What is artificial radioactivity?
- What are projectiles?
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