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Radioactivity

Radiation - a-particles.

Particles or waves which are emitted from a nucleus during decay
are called radiation.
The same word is also used for some electromagnetic waves
which have not come from radioactive decay.

An a-particle (alpha particle) is the same as the nucleus of a helium atom.
It consists of 2 protons and 2 neutrons.
Alpha Particle

An a-particle has by far the most mass of the three types of radiation.
It is the most likely to collide with other atoms which means that

1.  a-particles have the least penetrating ability and are easily absorbed
by paper, skin or a few centimetres of air.
2.  a-particles are the most ionising of the three types of radiation.

a-particles are likely to be emitted during the decay of heavy nuclei
which have a large number of protons and neutrons
(see examples).

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