Completion and extension of the periodic table of elements beyond uranium

In the 1940's, the search for elements beyond uranium led to the discoveries of the neutron-induced fission of uranium and of eleven trans-uranium radioelements, belonging to the actinide series. The best known of the actinide elements is plutonium. Plutonium undergoes neutron fission, as uranium, and, since 1940, humanity has been living in the nuclear age, the age of the release of the fantastic nuclear energy. These discoveries resulted from continuous research efforts on natural radioelements, initiated in 1898 by Pierre and Marie Curie, and on artificial radionuclides, initiated in 1934 by Frederic and Irene Joliot. Today, 118 elements are arranged into the modern versions of the periodic table. All the elements up to curium play a part in human activities. This paper describes how the progression of knowledge, thanks in particular to the heavy experimental means deployed in the USA before and during World War II, led to the completion and extension of the periodic table of elements. It focuses on the period 1937 to 1960 marked by the discoveries of manmade Tc (technetium), Pm (promethium), At (astatine), and of actinides from neptunium (Z=93) to lawrencium (Z=103). The discovery of Fr (francium) was the last discovery made in the line of the fruitful research on natural radioelements conducted in Europe. (author)