The process of discovering new elements has transformed from isolation from natural ores to creation in sophisticated laboratories. Today, a “new element” refers almost exclusively to a synthetic, radioactive atom with an atomic number greater than 92, known as a transuranic element. These elements are inherently unstable due to their large nuclei and do not exist naturally for any appreciable length of time. The modern method of discovery involves nuclear physics, where scientists construct these atoms one nucleus at a time, expanding the boundaries of the periodic table through artificial synthesis.
The Theoretical Framework for Discovery
The successful search for new elements began with Dmitri Mendeleev in 1869, who organized the known elements based on recurring patterns in their chemical properties. Mendeleev left gaps in his periodic table when an element’s properties did not fit the pattern based on atomic weight. He predicted the existence and properties of several undiscovered elements, such as eka-silicon (later Germanium), which lent credibility to his system.
This periodic arrangement was refined in the early 20th century by Henry Moseley, who used X-ray spectroscopy to measure the nuclear charge of the elements. Moseley established that the correct organizing principle was the atomic number (Z), which represents the number of protons in the nucleus. This provided a clear, sequential roadmap for physicists, allowing them to know precisely which atomic numbers were missing from the periodic table.
Key Figures in Creating Transuranic Elements
The first significant expansion of the periodic table in the modern era was spearheaded by American chemist Glenn Seaborg and his team at the University of California, Berkeley. Seaborg’s work began during the Manhattan Project, where his team first identified plutonium (Z=94) and americium (Z=95). His laboratory synthesized a total of ten transuranic elements, including curium (Z=96), berkelium (Z=97), and californium (Z=98), using particle accelerators to bombard heavy target materials.
Seaborg’s greatest conceptual contribution was the actinide concept, proposing that elements 89 (Actinium) through 103 form a new series, analogous to the lanthanides. This arrangement placed the actinides in a separate row below the main table, accurately predicting their chemical properties and guiding the discovery of elements like einsteinium (Z=99) and fermium (Z=100).
Intense international competition emerged, focusing on the creation of elements beyond Z=103. Major research centers included the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, and Germany’s GSI Helmholtz Centre for Heavy Ion Research. This competition, sometimes called the “Transfermium Wars,” involved disputes over credit for discoveries like rutherfordium (Z=104) and dubnium (Z=105), cementing these three laboratories as world leaders in nuclear synthesis.
The Technology of Superheavy Element Synthesis
Creating elements with Z greater than 103 requires overcoming the immense electrical repulsion between two positively charged nuclei, known as the Coulomb barrier. Scientists use particle accelerators, such as cyclotrons, to propel a beam of lighter “projectile” nuclei toward a heavy “target” nucleus at high speeds. The goal is nuclear fusion, where the two nuclei merge briefly to form a single, heavier, and highly unstable compound nucleus.
Two main techniques dominate superheavy element synthesis: hot fusion and cold fusion. After fusion, complex separators like SHIP or TASCA isolate the fleeting new atom from the abundant unreacted beam particles.
Hot Fusion
Hot fusion, largely pioneered by the Dubna team, involves bombarding a heavy actinide target, such as Californium or Curium, with a neutron-rich, medium-mass projectile like Calcium-48. This reaction creates a compound nucleus with high excitation energy. The nucleus stabilizes by emitting three to five neutrons.
Cold Fusion
Cold fusion, primarily used by the GSI and RIKEN laboratories, uses a lead or bismuth target, which are nuclei with tightly bound protons and neutrons. The projectile is typically a heavier ion. The resulting compound nucleus has a much lower excitation energy, stabilizing by emitting only one or two neutrons. Although cold fusion produces more stable initial nuclei, it yields less neutron-rich isotopes, which are less stable overall.
Establishing and Naming a New Element
A claimed discovery must undergo a rigorous, multi-year validation process before an element is officially recognized and added to the periodic table. Confirmation rests with the Joint Working Party (JWP), a committee formed by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP). The JWP reviews experimental data, focusing on whether the synthesis is reproducible and if the decay chain confirms the nucleus’s identity.
Once the JWP validates the discovery and assigns priority, the collaborating laboratory proposes a name and symbol. Elements awaiting official recognition are given a temporary systematic name based on their atomic number, such as Ununpentium (Uup) for element 115. IUPAC guidelines specify that a new element can be named only after:
- A mythological concept.
- A mineral.
- A place or country.
- A property.
- A scientist.
The proposed name then undergoes a five-month public review period before IUPAC grants final approval.