State the nature and any four properties of `alpha`-particle.

Explanation

Nature of `alpha`-particles
(1) An alpha particle is a helium nucleus, i.e., a doubly ionized helium atom. It consists of two protons and two neutrons.
(2) Mass of the `alpha cong 4u` Charge on the `alpha-"particle"=2 xx "charge on the proton"`
Properties of `alpha`-particles :
(1) Of the three types of radioactive radiations, `alpha`-particles have the maximum ionising power. It is about 100 times that of `beta`-particles and `10^(4)` times that of `gamma`-rays.
(2) They are deflected by electric and magnetic fields since they are charged particles. Their deflection is less than that of B-particles in the same field.
(3) They affect photographic plates.
(4) They cause fluorescence in fluorescent materials such as zinc sulphide.
(5) They emerge from the nuclei with tremendous speeds in the range of `(1)/(100)`th to `(1)/(10)`th of the speed of light in free space.