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.