Points to Remember

Nuclear Physics (Science)

Points to Remember

·                 This phenomenon of spontaneous emission of radiation from certain elements on its own is called 'natural radioactivity'.

·                 Curie is defined as the quantity of a radioactive substance,  which  undergoes  3.7  ×  1010 disintegrations in one second. This is actually close to the activity of 1 g of radium-226.

·                 Rutherford (Rd) is defined as the quantity of a radioactive substance which produces 106 disintegrations in one second.

1 Rd = 106 disintegrations per second.

·                 The SI unit of radioactivityis becquerel. It is defined as the quantity of one disintegration per second.

·                 Helium nucleus (2He4) consisting of two protons and two neutrons is known as alpha particle.

·                 Beta particles are electrons (-1e0), which are the basic elementary particles present in all atoms.

·                 Gamma rays are electromagnetic waves consisting of photons.

·                 A nuclear reaction in which an unstable parent nucleus emits an alpha particle and forms a stable daughter nucleus is called as 'alpha decay'.

·                 A nuclear reaction in which an unstable parent nucleus emits a beta particle and  forms a stable daughter nucleus is called as 'beta decay'.

·        The process of breaking (splitting) up of a heavier nucleus into two smaller nuclei with the release of a large amount of energy is called'nuclear fission'.

·                 The energy released in a nuclear fission process is about 200 MeV.

·                 There are some radioactive elements which can be converted into a fissionable material. They are called as 'fertile materials'. e.g. Uranium-238, Thorium-232, Plutonium-240.

·                 Controlled chain reaction is used in a nuclear reactor to produce energy in a sustained and controlled manner.

·                 The process in which two lighter nuclei combine to form a heavier nucleus is termed as 'nuclear fusion'.

·                 Nuclear fusion or thermonuclear reaction is the source of light and heat energy in the Sun and other stars.

·                 The safe limit of receiving the radiation is about 100 mR per week.