ABSTRACT
It is a hundred years since the discovery of X-rays by Wilhelm Roentgen (1895) and nearly as long since the discovery of natural radioactivity of uranium by Henri Becquerel (1896). Pierre and Marie Curie came a little later in their discovery of the radioactivity of radium. Until recently, their name was honoured with the unit of radioactivity but a more soundly based physical definition on the basis of a nuclide’s disintegration rate became necessary, and that honour reverted to Becquerel himself.
