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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.
Sub Topics
Characteristics of Alpha Rays (i.e., a - particles)
Characteristics of Beta Rays (i.e., b - Particles)
Characteristics of Gamma (g) Rays
Characteristics of Alpha Rays (i.e., a - particles)
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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
2
He
4
.
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 10
7
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)
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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
-1
e
0
.
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 10
8
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
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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
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