Page 315 - General Knowledge

GENERAL KNOWLEDGE 2019

Nuclear Physics
 The nucleus consists of the elementary particles, protons and neutrons which are known as
nucleons.
 A proton has positive charge of the same magnitude as that of electrons and its rest mass is
about 1836 times the mass of an electron.
 A neutron is electrically neutral, whose mass is almost equal to the mass of the proton.

 The nucleons inside the nucleus are held together by strong attractive forces called nuclear
forces.
Classification of Nuclei
 Isotopes: Isotopes are atoms of the same element having the same atomic number Z but
different mass number A.
 The nuclei 1H1, 1H2 and 1H3 are the isotopes of hydrogen.
 Isobars: Isobars are atoms of different elements having the same mass number A, but
different atomic number Z. The nuclei 8O16 and 7N16 represent two isobars. Since isobars
are atoms of different elements, they have different physical and chemical properties.
 Isotones: Isotones are atoms of different elements having the same number of neutrons.
6C14 and 8O16 are some examples of isotones.

Radioactivity
 The phenomenon of spontaneous emission of highly penetrating radiations such as α, β and
γ rays by heavy elements having atomic number greater than 82 is called radioactivity and
the substances which emit these radiations are called radioactive elements.
 Three types of radiations emitted by radioactive elements.
 - Rays- It consists of alpha particles, which are doubly ionised helium ion.
 - Rays- It consists of fast moving electrons.
 - Rays- These rays are electromagnetic rays.

Nuclear Binding Energy
 In Nucleus, Proton and Neutron are contained in a small sphere.
 Due to such small distance between two protons, they exert a very large force of repulsion
on each other.
 Therefore, to prevent nucleus from bursting, a certain amount of energy needed to bind the
nucleus. This energy needed is known as Binding Energy.
 When nucleus is formed, the mass of nucleons forming it decreases. This mass defect
provides the required binding energy. The energy equivalent to mass defect is called Binding
Energy.
 Binding Energy of a nucleus may also be defined as the amount of work required to
separate the nucleons at infinite distance. It is the measure of stability of nucleus.

Half Life Period and Mean Life
 The half-life period of a radioactive element is defined as the time taken for one half of the
radioactive element to undergo disintegration.

 The half-life period is inversely proportional to its decay constant.
 When the radioactive substance is undergoing disintegration, the atom which disintegrates
at first has zero life and that disintegrates at last has infinite life. The actual life of each atom

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