In 1919, Ernest Rutherford discovered the first example of an artificial nuclear transformation. He directed alpha particles from a naturally radioactive source into a container of nitrogen gas. Rutherford found that the alpha particles collided with nitrogen atoms and brought about a change in their atomic nuclei. Oxygen-17 and protons were formed:

14 4 1 17 N + He ——-> H + O 7 2 1 8

This procedure soon became popular with other researchers who studied the effects of naturally produced alpha particles on other materials. (Before the invention of particle accelerators, alpha particles were essentially the only particles available for such research.) One important example of this kind of research was James Chadwick's discovery of the neutron as the result of the bombardment of beryllium with alpha particles:

9 4 12 1 Be + He ———-> C + n 4 2 6 0

In 1934, Frédéric and Irène Joliot-Curie observed an unusual variation of the...