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The spontaneous breaking up of certain unstable nuclei, accompanied by the emission of one or more types radiation.


Scientist who discovered radiation from uranium salts

Marie and Pierre Curie

Scientists who researched radioactivity and discovered polonium and radium

Alpha particles

Made of 2 protons + 2 neutrons (helium nuclei) with a positive charge. Little penetrating ability (stopped by a sheet of paper)

Alpha decay

When an isotope undergoes this, its atomic number decreases by 2, while its mass number decreases by 4.


Alpha emitter used in smoke detectors

Beta particles

Electrons with a negative charge, formed when a neutron decays into a proton and an electron. Medium penetrating ability (stopped by 5mm of aluminium)

Beta decay

When an isotope undergoes this, its atomic number increases by 1, while its mass number remains unchanged.


Beta emitter used in to date archaeological artefacts

Gamma rays

High energy electromagnetic radiation which are not deflected by magnetic or electric fields, High penetrating ability (only stopped by several cms of lead)


Gamma emitter used to treat cancer or in food preservation as it kills disease causing organisms by irradiation


An atom with an unstable nucleus (radionuclide).


The time taken for half of the atoms in a sample of the radioactive isotope to decay.

Background radiation

The low level of radiation that surrounds us at all times. 90% comes from natural sources such as Radon gas

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