What is radioactivity?
Editorial review 2026
What distinguishes a radioactive atom from an ordinary atom is that unique moment when its nucleus transforms by emitting radiation. This emission occurs after highly variable periods of time, which can reach billions of years. A radioactive atom can be compared to a soldier who would fire only once in his lifetime and … in any direction. If it finds itself in an excited state, it accompanies its shot with a de-excitation gamma ray, in another direction.
Apart from this unpredictable moment, a radioactive atom behaves exactly like an ordinary atom, with the same physical, chemical or biological properties. Throughout its entire existence, it is neither more mobile nor more harmful than its non-radioactive counterparts.
Why are some nuclei unstable? Why do they emit one type of radiation rather than another? What is the origin of the radiation to which we are exposed? At what rate do they decay and for how long? What does their radioactive activity represent? How do they interact as they pass through matter? What are the main radioactive nuclei?
These are the questions that this presentation of the phenomenon of radioactivity attempts to answer.
« Mr Prudent discovers radioactivity »
Marie Curie and Ernest Rutherford
Marie Curie and Ernest Rutherford discovered, with others, radioactivity and the nucleus of the atom in the early twentieth century.
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ACCESS TO CHAPTERS : SUMMARY
– Dicoveries of radioactivity and of the nucleus : Radium and polonium, Marie Curie and Ernest Rutherford. The exploration of the Infinitely small. Artificial radioactivity. The discovery of the neutron of the nuclear fission.
– The atomic world : A review of notions concerning atoms. The atom and its nucleus.
– Radioactive nuclei : Unstable nuclei. The causes of their unstability. Nuclear forces.
– Alpha (α), bêta (β) and gamma (γ) rays : The three types of nuclei radiation ; their characteristics.
– Half-lives and activities. Radioactivity decreases with time. The laws of radioactive decay.
– Effects of radiation : Interactions of charged and neutral particles through matter. Atoms ionization. Macroscopic effects.
– Neutron radiation : Slow and fast neutrons
– Main radioactive nuclei : From uranium, radium, plutonium, to carbon-14, iodine-131, cesium-137.