Frederic Joliot-Curie

There is no doubt that radium is transformed spontaneously into an active gas, radon, emitting at the same time alpha particles, or helions. ”

Astronomers sometimes observe that a star of medium magnitude increases suddenly in size; a star invisible to the naked eye may become very brilliant and visible without any telescope - the appearance of a Nova. ”

The first unquestionable proofs of the transformation of elements into different chemical elements have been provided by the study of the phenomena of radioactivity. ”