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What is radioactivity?

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Atoms are made of three types of sub-atomic particle: neutrons and protons in the nucleus and electrons orbiting the nucleus.

Some materials are radioactive because the nucleus of each atom is unstable and gives out nuclear radiation in the form of alpha particles, beta particles or gamma rays. The radiation can be detected using a Geiger counter.

Radioactive substances

Radioactivity

atoms have a small central nucleus surrounded by electrons

The structure of the atom

Atoms are made up of two main parts, the nucleus and orbiting electrons.

The nucleus contains two types of particles called neutrons and protons. As protons, neutrons and electrons are the building blocks of atoms they're called sub-atomic particles.

Properties of sub-atomic particles

ParticleRelative massRelative charge
Proton1+1
Neutron10
ElectronAlmost zero-1

Some materials are radioactive because the nucleus of each atom is unstable and can decay (split up) by giving out nuclear radiation in the form of alpha particles, beta particles or gamma rays. The nuclear radiation given off can be detected using a Geiger counter. The number of nuclei that decay and give off radiation every second is called the activity of the material and is measured in becquerels (Bq).

Example

If a radioactive material has an activity of 200Bq, in 1 second 200 of its nuclei will decay and give off radiation. In 1 minute 12000 (=200 x 60) nuclei will decay.

The activity of a radioactive material will decrease with time. This will be shown by a falling count rate, measured using the Geiger counter.

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