Learning Objectives After learning this unit, students will be able to Define radio activity. Distingush between natural and artificial radio activity. Relate the properties of alpha, beta and gamma rays. State Soddy and Fajan’s displacement law of nuclear disintegration.
Understand the concept of nuclear fission and nuclear fusion. Identify fissionable materials. Analyze controlled and uncontrolled chain reactions. Explain the principle of atom bomb and hydrogen bomb.
List the uses of radio activity. Understand the components of a nuclear reactor. Identify the precautionary measures while handling a radioactive material. Nuclear physics .
RADIOACTIVITY . . Discovery of radioactivity In , French physicist Henri Becquerel finished his research for the week and stored a certain amount of uranium compound away in a drawer for the week end. By chance, an unexposed photographic plate was also stored in the same drawer.
After a week he returned and noticed that the film had been exposed to some radiation. He discovered that he could reproduce the effect whenever he placed uranium near a photographic film. Apparently, uranium radiated something that could affect a photographic plate. This phenomenon was called as Radioactivity .
Uranium was identified to be a radioactive element. Two years later, the Polish physicist Marie Curie and her husband Pierre Curie detected radioactivity in 'Pitchblende', a tiny black substance. They were not surprised at the radioactivity of pitchblende, which is known as an ore of uranium. Later, they discovered that the radiation was more intense from pure uranium.
Also, it was found that the pitchblende had less concentration of uranium. They concluded that some other substance was present in pitchblende. After separating this new substance, they discovered that it had unknown chemical properties and it also emitted radiations spontaneously like uranium. They named this new substance as 'Radium' .The radioactive elements emit harmful radioactive radiations like alpha rays or beta rays or gamma rays.
. . Definition of radioactivity The nucleus of some elements is unstable. Such nuclei undergo nuclear decay and get converted into more stable nuclei.
During this nuclear reaction, these nuclei emit certain harmful radiations and