All simple smoke detectors contain a radioactive element and will react if placed close i.e. touching a contaminated object or person.
Sometimes the nucleus of an atom is unstable.
A change will occur in the nucleus to make it more stable.
The change is called a decay.
When a nucleus decays, it will emit (give out) radioactivity.
Radioactive decay is a random process which gives out heat.
There are three types of radioactivity, called a (alpha), b (beta) and g (gamma).
A radioactive nucleus will emit either an alpha particle or a beta particle or a gamma ray.
After an alpha particle or a beta particle has been emitted, the atomic number of the atom will have changed.
The atom will have become a different element.
An alpha or beta emitter might also emit gamma radiation.
Radioactivity can be both harmful and useful.
The rate of decay (half-life) can be used to find out how old things are.
The energy released from a nucleus during fission can be used to generate electricity.
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