The key difference between natural and artificial radioactivity is that the natural radioactivity in the form of radioactivity takes place on its own in nature whereas when it is induced by man in laboratories, it is called artificial radioactivity.
Man did not invent the process of radioactivity; it was there, existing in the universe since time immemorial. But it was a chance discovery by Henry Becquerel in 1896 that the world came to know about it. Furthermore, the scientist Marie Curie explained this concept in 1898 and earned a Nobel Prize for her work. We refer the type of radioactivity taking place in the world (read stars) on its own as natural radioactivity while that which man induces as artificial radioactivity.
