Irene Joliot-Curie

The time necessary for the disappearance of half the atoms, called the half-life, is a fundamental characteristic of each radio-element; according to the substance, the value of the half-life varies between a fraction of a second and millions of years.

It was at the beginning of 1934 while working on the emission of these positive electrons that we noticed a fundamental difference between that transmutation and all the others so far produced; all the reactions of nuclear chemistry induced were instantaneous phenomena, explosions.