From 1996 to 1998, the centennial of the discovery of radioactivity was celebrated in France. Exhibitions were held, meetings took place, films were shown and symposia were organized. The opportunity was also taken to inform the general public of the consequences of this major discovery; the improved understanding of the atomic structure that resulted from it, and the improvements to our quality of life that understanding has brought.
At the turn of the last century and before the discovery of radioactivity, the atom was an entirely hypothetical concept, whose very existence was doubted in the scientific community. It was only in 1906 that the French physicist Jean Perrin was conclusively able to demonstrate its existence.
Marie Curie and her husband Pierre had been curious about what was happening inside the atom, and postulated that radioactivity was an atomic phenomenon. In a world where the atom was held to be the fundamental, indivisible unit of matter, the proposal that an atom was capable of decaying or of transforming amounted to heresy.
The following decades saw very many great experimentalists attempting to discover the true nature of the atom. Using the newly-discovered phenomenon of radioactivity, they were able to deduce that an atom consisted of an extremely dense central nucleus surrounded by orbiting electrons. Further experimentation revealed even more fundamental units of matter: the nucleus consists of neutrons and protons bound together very tightly, and both neutrons and protons are composed of even smaller “quarks”. At around the same time, physicists proposed the existence of a particle known as the ‘neutrino’; for which no direct evidence existed, but whose presence made the physics work. The neutrino would be discovered 25 years later, exactly as predicted.
A Page of History : Vidéo - Source Ganil