General Characteristics of Natural Radioactivity

• It is a nuclear phenomenon.

• It is due to the instability of the nucleus.

• It is a spontaneous, continuous and irreversible process.

• It is independent of external factors such as pressure, temperature, state of substance, electrical field, magnetic field, catalyst etc.

• A radioactive element emits α β and γ radiations.

• Due to the emission of an α particle, atomic number decreases by 2 units and mass number decreases by 4 units.

• Due to the emission of β particle, atomic number increases by 1 unit but the mass number remains the same.

• A radioactive element does not emit α and β particles simultaneously.

• The original radioactive nucleus or element is called a parent element and the new element formed is known as daughter element.

• The physical and chemical properties of daughter element are different than that of the parent element.

Characteristics of Alpha Rays (i.e., a - particles)

• Alpha rays consist of stream of positively charged particles carrying charge of +2 units and a mass of four units on the atomic weight scale (i.e., 4 amu). They consist of 2 protons and 2 neutrons. In other words, these particles are helium nuclei and therefore indicated as ₂He⁴.

• They affect photographic plate

• They are deflected only slightly towards the negative plate in electric field. They are also deflected by magnetic field.

• These particles can ionize gases. Alpha rays have maximum ionizing power.

• They have a velocity of the order of 1 x 10⁷ m s^-1.

• They have very little penetrating power.

• By emission of an - particle, atomic number of nucleus decreases by 2 units and mass number by 4 units.

Characteristics of Beta Rays (i.e., b - Particles)

• Beta rays are made up of streams of negatively charged particles similar to electrons. Thus, - particle has a unit negative charge and a negligible mass. They are electrons. Hence, - particle is represented as _-1e⁰.

• They affect photographic plate.

• They get deflected to the maximum extent towards the positive plate in electric field. They are also deflected by magnetic field.

• Their ionising power is less than that of - rays. (It is about one hundredth of - particles).

• Their velocity varies with the source and is almost equal to the velocity of light, about 2.7 x 10⁸ m/s.

• Their penetration power is about 100 times more than that of - particles.

• By emission of a b - particle, atomic number of nucleus increases by one whereas mass number remains same. (this is because, the ejection of a b - particle results from the transformation of a neutron into a proton and an electron ).

Characteristics of Gamma (g) Rays

• They are electromagnetic radiations like X-rays having very short wavelength, in the range of 10^-10 m to 10^-13 m.

• They affect photographic plate.

• They are unaffected by electric and magnetic fields.

• Their ionizing power is low, (about one hundredth of  b - particles).

• Their velocity is same as that of light.

• Their penetrating power is very high, about 100 times more than that of  b - particles. Hence, they are also known as hard rays.

• When a and b particles are emitted by an atom, there is always a rearrangement in the nucleus and during this process some energy is given out in the form of  g - rays. Thus, emission of gamma rays accompanies virtually all nuclear reactions. There is no change in the mass number or atomic number of the nucleus as g - rays have negligible mass.

Comparison between α, β particles and γ rays

Sl.No	Alpha	Beta	Gamma
1.	α - particle is the helium nucleus (2He4)	β - particle is an electron (-1e°).	γ - particle is an electromagnetic radiation
2.	It is +vely charged.	It is -vely charged.	It has no charge.
3.	The mass of each α - particle is 4 amu about 1/1836 amu	The mass of each β - particle is negligible.	It has no mass.
4.	Its velocity is less 107 cm/s.	Its velocity is less than the velocity of light and is equal to 2.7 x 108 m/s	Its velocity is the same as that of light and is equal to 3x108 m/s,
5.	Its has maximum ionization power. It is about 100 times more than that of β - particles	Its ionization power is about 100 times more than that of γ -rays.	The ionization power is the least
6.	Penetrating power is the least.	Penetrating power is less but 100 times more than penetrating power of α - particles	Penetrating power is maximum i.e., 100 times more than that of β - particles.