Artificial Radioactivity:

Since radioactivity was discovered in naturally occurring substances, during later years efforts were made to produce artificial radioactivity by bombarding stable nuclides (used as target) with nuclear particles (primary α-particles).  In 1919, Ernest Rutherford first produced nuclear transmutation by α-particle bombardment on nitrogen.

¹⁴N + ⁴He       → ¹⁷O + ¹H

However, the reaction product ¹⁷O, being stable isotope of oxygen that was not found to be radioactive.  It was not until 1934 while Irene Curie (daughter of Pierre and Marie Curie) and her husband Frederic Joliot discovered artificial radioactivity by the α- particle (obtained from polonium) bombardment on aluminium foil.

²⁷Al + ⁴He → ³⁰P + ¹n

In this case the reaction product was 30P which became first artificially produced radionuclide.  It was found to emit positron (β+) which had been discovered only two year earlier (in 1932 by Andersson).  That gave enormous impetus to the field of nuclear reaction studies.