1. Radioactivity is the spontaneous and random emission of radioactive rays from unstable radioactive materials after which they become more stable.

2. The process is said to be spontaneous because it is not influenced by any physical factors such as temperature, pressure, time, etc.

3. A nucleus is unstable if it is too big. All nuclei with z > 83 or A> 209 are unstable.

4. The emission of radioactive rays is random means that

    • Emission occurs at irregular intervals.
    • Emission does not occur at the same means.

5. There are three different types of radioactive emissions.

    • Alpha particle- a
    • Beta particle- B
    • Gamma ray-r

6. Table below shows the characteristics of alpha particle, beta particle, and gamma particle.


Alpha particle

Beta particle

Gamma ray


Positively charged helium nucleus, He

Negatively charged electron, e

Neutral electromagnet ray

In an electric field

Bends to the negative plate

Bends to the positive plate

Does not bend, showing that it is neutral.

In magnetic field

Bends a little showing that it has a big mass. Direction of the bend indicates that it is positively charged.

Bends a lot showing that it has a small mass. Direction of the bend indicates that it is negatively charged.

Does not bend showing that it is neutral.

Ionising power




Penetrating power




Stopped by

A thin sheet of paper

A few millimeters of aluminium

A few centimeters of lead or concrete

Range in air

A few centimeters

A few metres

A few hundred metres


1/20 X the speed of light, c

3%-99% of the speed of light, c

The speed of light,c

1 comment:

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