Synthetic Elements: The Man-Made Additions to the Periodic Table

How Synthetic Elements Are Made

Two primary methods produce synthetic elements, each suited to different regions of the periodic table. Neutron capture, used in nuclear reactors, bombards existing heavy elements with neutrons. When a nucleus absorbs a neutron, it may undergo beta decay, converting a neutron to a proton and advancing to the next element. This process produced neptunium and plutonium from uranium in the early 1940s and has been used to create elements up to fermium (element 100). The advantage of reactor-based synthesis is that it can produce weighable quantities of material: kilograms of plutonium and milligrams of californium are manufactured routinely for industrial and research use.

For elements heavier than fermium, hot and cold fusion reactions in particle accelerators are required. In hot fusion, a lighter projectile ion (often calcium-48, chosen for its doubly magic nucleus that promotes fusion) is accelerated to high velocity and collided with a heavy target nucleus (such as berkelium-249 or californium-249). If the two nuclei merge and enough neutrons are emitted to stabilize the compound nucleus, a new superheavy element is formed. Cold fusion uses slightly lighter targets (lead-208 or bismuth-209) and heavier projectiles, producing compound nuclei with less excitation energy and lower neutron emission. Both methods produce at most a few atoms per experiment, sometimes only one atom over weeks of continuous bombardment.

The detection challenge is enormous. When only a handful of atoms are produced, identification relies entirely on observing the characteristic alpha decay chains. Each superheavy atom decays by emitting a series of alpha particles (helium-4 nuclei), and the energies and timing of these emissions create a fingerprint unique to each element. If the decay chain connects to a previously known isotope, the parent element is confirmed. This technique can identify a single atom, but it requires extremely sensitive detectors and careful analysis to distinguish real events from background noise.

Notable Synthetic Elements

Technetium (Tc, element 43) was the first element synthesized. Carlo Perrier and Emilio Segre produced it in 1937 by bombarding molybdenum with deuterons in Ernest Lawrence's cyclotron at Berkeley. Its name comes from the Greek "technetos," meaning artificial. Despite having no stable isotopes, technetium-99m is the most widely used radioisotope in medical diagnostic imaging, with over 30 million procedures performed annually. Its 6-hour half-life provides enough time for imaging while limiting patient radiation exposure, and its 140 keV gamma emission is ideal for detection by gamma cameras.

Promethium (Pm, element 61) is the only lanthanide with no stable isotopes. It was definitively identified in 1945 among fission products from a nuclear reactor at Oak Ridge. All promethium isotopes are radioactive with half-lives too short for the element to survive from Earth's formation. Promethium-147 (half-life 2.6 years) has been used in luminous paint for watches and instruments, and as a beta-particle source for thickness gauges in manufacturing.

Plutonium (Pu, element 94) is the best-known synthetic element. Glenn Seaborg's team produced it in 1940 by bombarding uranium-238 with deuterons. Plutonium-239 undergoes fission with slow neutrons, making it suitable for both nuclear weapons and reactor fuel. The first nuclear weapon tested (Trinity, 1945) and the bomb dropped on Nagasaki used plutonium-239. Approximately 100 tonnes of reactor-grade plutonium are produced worldwide each year as a byproduct of uranium fission in power plants. Plutonium-238, a different isotope, generates heat through radioactive decay and powers deep-space probes like the Voyager spacecraft and the Perseverance Mars rover.

The Transfermium Elements (101-118) were produced at a handful of laboratories worldwide: the Lawrence Berkeley National Laboratory in California, the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, the GSI Helmholtz Centre in Darmstadt, Germany, and RIKEN in Japan. Competition between these labs to synthesize and confirm new elements was sometimes fierce, leading to naming disputes that took decades to resolve. The "Transfermium Wars" of the 1990s saw conflicting claims between American, Russian, and German teams for elements 104 through 109, eventually settled by IUPAC through compromise names.

The Island of Stability

Nuclear physics predicts that certain combinations of protons and neutrons form "magic numbers" that create exceptionally stable configurations, analogous to the noble gas electron configurations in atomic physics. The most commonly cited nuclear magic numbers are 2, 8, 20, 28, 50, 82, and 126. A nucleus with a magic number of both protons and neutrons is "doubly magic" and extremely stable. Lead-208, with 82 protons and 126 neutrons, is the heaviest stable doubly magic nucleus known.

Theorists predict an "island of stability" around proton number 114 (flerovium) and neutron number 184, where superheavy nuclei may have half-lives of minutes, days, or even years instead of the milliseconds typical of current superheavy elements. Flerovium-298 (114 protons, 184 neutrons) is a prime candidate, but current synthesis methods cannot produce nuclei with enough neutrons to reach this island. The most neutron-rich flerovium isotopes produced so far have only 175 neutrons, falling short of the predicted stability peak.

Current experimental evidence provides tentative support for the island's existence. Elements 114 through 118 have somewhat longer half-lives than elements 110 through 113, suggesting an approach to enhanced stability. If the island of stability proves accessible with future technology, its elements could have chemical properties worth studying in bulk, unlike the current superheavy elements that are identified atom by atom. Some theorists predict that island-of-stability elements might have unique chemical properties driven by extreme relativistic effects on their electron shells.

Practical Uses of Synthetic Elements

Despite their exotic origins, several synthetic elements have found practical applications. Beyond technetium's medical imaging role and plutonium's use in energy and space exploration, other synthetic elements serve specific niches. Americium-241 (element 95) is present in virtually every household smoke detector, where its alpha radiation ionizes air molecules to create a current that is interrupted by smoke particles. Californium-252 (element 98) is a portable neutron source used in oil well logging, moisture detection in soil, and startup neutron sources for nuclear reactors. Curium-244 (element 96) has been used as an alpha particle source in X-ray spectrometers on Mars rovers to analyze rock composition.

Challenges and Future Directions

Each successive element is harder to create. Production cross-sections (the probability that a collision will produce the desired element) drop dramatically with increasing atomic number. Oganesson (element 118) was produced by firing calcium-48 at californium-249, yielding a total of about five atoms across several experiments. The target materials themselves are extraordinarily difficult to produce; berkelium-249 for tennessine synthesis required 250 days of neutron irradiation at Oak Ridge National Laboratory, and the entire world's production of berkelium was consumed in a single experiment.

The search for elements 119 and 120 is underway at JINR in Russia and RIKEN in Japan. These experiments use new beam-target combinations and upgraded accelerators to increase collision rates. Element 119 would begin the eighth period of the periodic table and would be expected to be an alkali metal, while element 120 would be an alkaline earth metal. Success may require years of continuous running and the development of new detection methods capable of identifying a single atom among trillions of unproductive collisions. The newest elements guide covers the most recent additions in detail.