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| General Characteristics of Natural Radioactivity |
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 It is a nuclear phenomenon. |
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 It is due to the instability of the nucleus. |
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 It is a spontaneous, continuous and irreversible process. |
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 It is independent of external factors such as pressure, temperature, state of substance, electrical field, magnetic field, catalyst etc. |
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 A radioactive element emits  and  radiations. |
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 Due to the emission of an  particle, atomic number decreases by 2 units and mass number decreases by 4 units. |
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 Due to the emission of  particle, atomic number increases by 1 unit but the mass number remains the same. |
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 A radioactive element does not emit  and  particles simultaneously. |
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The original radioactive nucleus or element is called a parent element and
the new element formed is known as daughter element.. |
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 The physical and chemical properties of daughter element are different than that of the parent element. |
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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 2He4. |
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 They affect photographic plate |
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 They are deflected only slightly towards the negative plate in electric field. They are also deflected by magnetic field. |
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These particles can ionize gases. Alpha rays have maximum ionizing power. |
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 They have a velocity of the order of 1 x 107 m s-1. |
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 They have very little penetrating power. |
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 By emission of an  - particle, atomic number of nucleus decreases by 2 units and mass number by 4 units. |
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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 -1e0. |
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 They affect photographic plate. |
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 They get deflected to the maximum extent towards the positive plate in electric field. They are also deflected by magnetic field. |
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 Their
ionising power is less than that of  - rays. (It is about one hundredth of  - particles). |
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 Their velocity varies with the source
and is almost equal to the velocity of light, about 2.7 x 108 m/s. |
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 Their penetration power is about 100 times more than that of  - particles. |
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 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
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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. |
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 They affect photographic plate. |
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 They are unaffected by electric and magnetic fields. |
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 Their ionizing power is low, (about one hundredth of
b - particles). |
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 Their velocity is same as that of light. |
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 Their penetrating power is very high, about 100 times more than that of
b - particles. Hence, they are also known as hard rays. |
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 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. |
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Comparison between  particles and  rays |
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