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Radioactive substances

An atom of any given element consists of a nucleus containing a number of protons and neutrons. The nucleus is surrounded by electrons.

The half-life of a radioactive isotope is the time taken for half its radioactive atoms to decay.

There are three main types of radiation, called alpha, beta and gamma radiation, which all have different properties. Radiation can damage cells and make them cancerous. Very high doses of radiation can kill cells. It can be detected using photographic film or a Geiger-Muller tube. Radiation badges are used to monitor the level of radiation that people who work with radioactive sources are exposed to.

Radiation has many practical uses. It can be used in medicine to trace where certain chemicals collect in the body, indicating disease, and also in industry, where it can be used to control measuring equipment.

Atoms and isotopes

The nuclear model

the proton and neutron are within the nucleus which is within the centre of the atom, the elctrons are on the edges of the atom

Structure of the atom

Atoms contain three sub-atomic particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus at the centre of the atom, and the electrons are arranged in energy levels or shells around the nucleus.


All the atoms of a given element have the same number of protons and electrons. However, the number of neutrons can vary. Atoms of the same element that have different numbers of neutrons are called isotopes of that element. The diagram shows three hydrogen isotopes.


1 proton, 0 neutron, 1 electron


The different isotopes of an element have identical chemical properties. Some isotopes, however, are radioactive. This means that they give out radiation from their nuclei. This happens all the time, whatever is done to the substance. For example, the radiation is still given out if the substance is cooled down in a freezer, or takes part in a chemical reaction.

Back to Radiation and the Universe index

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