Synthetic elements

Synthetic elements. In chemistry and nuclear physics, synthetic elements are those that do not occur naturally on Earth and must be created artificially through human-induced nuclear reactions. All known synthetic elements are radioactive and have atomic numbers greater than that of uranium, which is the heaviest naturally occurring primordial element. The study and creation of these elements expands the periodic table and tests the limits of atomic theory and nuclear stability.

Definition and characteristics

Synthetic elements are defined by their absence in the natural solar environment, requiring artificial production in facilities like particle accelerators or nuclear reactors. A key characteristic is their placement on the periodic table beyond uranium (atomic number 92), a region often termed the transuranium elements. While some transuranic isotopes, like plutonium-244, have been found in trace amounts in nature, they are considered primordial rather than naturally occurring in significant quantities. These elements are typically produced in extremely small quantities, often atom-by-atom, and possess very short half-lives relative to the age of the Earth, leading to their decay if ever formed naturally. Their chemical properties, however, often follow trends predicted by the periodic table, allowing them to be placed in groups such as the actinide series or the transition metal block.

Discovery and synthesis

The discovery of synthetic elements began in the 20th century with the work of scientists like Enrico Fermi and Edwin McMillan. The first synthetic element, neptunium (element 93), was produced by McMillan and Philip Abelson in 1940 by bombarding uranium-238 with neutrons at the University of California, Berkeley. Subsequent discoveries, such as plutonium by Glenn T. Seaborg, utilized similar methods in reactors. Heavier elements are synthesized primarily via particle accelerators, where a heavy target nucleus is bombarded with a beam of lighter, high-energy ions. Major research institutions leading this work include the Joint Institute for Nuclear Research in Dubna, the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, and the Lawrence Berkeley National Laboratory. The synthesis process often results in isotopes that decay through a series of alpha decay and spontaneous fission events, which are detected using sophisticated apparatus like the gas-filled separator.

Stability and decay

The stability of synthetic elements decreases dramatically with increasing atomic number due to growing proton-proton repulsion within the nucleus, a challenge to the nuclear shell model. Most have half-lives ranging from minutes to milliseconds, though some isotopes in theoretical regions of enhanced stability, predicted by the island of stability hypothesis, may exist longer. This hypothesis, associated with physicists like Georgy Flerov, suggests that nuclei with certain "magic numbers" of protons and neutrons will be relatively more stable. Decay occurs predominantly through alpha decay, beta decay, or spontaneous fission, with the latter becoming increasingly dominant for the heaviest elements. The study of these decay chains, including the identification of daughter nuclides, is crucial for confirming the creation of a new element and understanding the forces at the limits of nuclear existence.

Applications and research

Practical applications of synthetic elements are limited by their scarcity, cost of production, and radioactivity, but several have found important uses. Plutonium-239 is a key fissile material in nuclear weapons and as fuel in some nuclear reactors, such as breeder reactors. Americium-241 is used in household smoke detectors, while californium-252 serves as a potent portable neutron source for neutron activation analysis in mining and material science. Research into heavier elements, like those in the transactinide element series including rutherfordium and darmstadtium, primarily advances fundamental science, testing quantum mechanical models and the periodic table's predictive power. This work also contributes to technologies in nuclear medicine and the understanding of stellar nucleosynthesis processes in extreme environments like supernovae.

List of synthetic elements

The list of entirely synthetic elements includes all elements with atomic numbers from 93 to 118. This encompasses the actinides from neptunium (93) to lawrencium (103), and the transactinide elements from rutherfordium (104) onward. Notable entries include plutonium (94), curium (96), berkelium (97), californium (98), and einsteinium (99), named for scientists and institutions like Marie Curie, the University of California, Berkeley, and the state of California. The most recently synthesized and named elements are nihonium (113), moscovium (115), tennessine (117), and oganesson (118), recognized by the International Union of Pure and Applied Chemistry. Elements like technetium (43) and promethium (61), while not naturally stable on Earth, are not typically classified as synthetic in this strict sense, as their isotopes are produced in stars and can be found in trace amounts from uranium fission. Category:Chemical elements Category:Nuclear chemistry Category:Synthetic elements