The scientific community at Berkeley, primarily the Lawrence Berkeley National Laboratory (LBNL), established a major legacy in the history of the Periodic Table. Beginning in the 1930s, researchers pioneered methods to manufacture new, heavier elements that do not occur naturally on Earth. This work extended the boundaries of known elements beyond the natural limit of uranium and made Berkeley the global center for the synthesis of these heavy, unstable atoms.
The Total Count and the Elements Discovered
The research teams at Berkeley are credited with the discovery of 16 elements. This count includes elements where a Berkeley team was the primary discoverer or a key collaborator in the initial synthesis. The effort began with elements 93 and 94, neptunium (\(\text{Np}\)) and plutonium (\(\text{Pu}\)), and extended through the subsequent transuranium elements.
The synthetic elements span atomic numbers 43 to 106. Berkeley researchers discovered or co-discovered nearly all of the transuranium elements created between 1940 and 1974, including Americium (95, \(\text{Am}\)), Curium (96, \(\text{Cm}\)), Berkelium (97, \(\text{Bk}\)), and Californium (98, \(\text{Cf}\)).
Other discoveries include:
- Einsteinium (99, \(\text{Es}\)) and Fermium (100, \(\text{Fm}\)), found in thermonuclear test debris in 1952.
- Mendelevium (101, \(\text{Md}\)), Nobelium (102, \(\text{No}\)), and Lawrencium (103, \(\text{Lr}\)).
- Rutherfordium (104, \(\text{Rf}\)), Dubnium (105, \(\text{Db}\)), and Seaborgium (106, \(\text{Sg}\)).
- Two lighter elements, Technetium (43, \(\text{Tc}\)) and Astatine (85, \(\text{At}\)).
The discovery of Seaborgium (106) was notable because it was the first element named after a living scientist, Glenn Seaborg.
Creating the Elements: The Science of Synthesis
The creation of these new elements relied on a process called nuclear fusion, which was made possible by particle accelerators. The fundamental approach involved bombarding a heavy target element with a beam of smaller, accelerated particles, causing the nuclei to combine. This method overcomes the strong electrostatic repulsion between two positively charged nuclei, which naturally prevents them from merging.
The invention of the cyclotron by Ernest Lawrence provided the tool to accelerate particles to extremely high speeds. The energetic beam was directed at a target material, like uranium or plutonium metal. When the accelerated particle struck a target atom’s nucleus, the two nuclei fused for a fleeting moment, resulting in a new, heavier element.
The resulting synthetic atoms existed for only fractions of a second before decaying radioactively. Identifying these new elements required sophisticated and rapid chemical separation techniques to isolate and characterize the few newly formed atoms. While initial products used Lawrence’s earliest cyclotrons, the synthesis of heavier elements later demanded larger and more powerful machines, such as the 60-inch cyclotron and the Heavy Ion Linear Accelerator (HILAC).
The Scientific Context of the Discoveries
The pursuit of synthetic elements began with the founding of the Radiation Laboratory, or “Rad Lab,” by physicist Ernest Lawrence. Lawrence’s invention of the cyclotron, a circular particle accelerator, provided the infrastructure that made the discoveries possible. This facility attracted a group of interdisciplinary scientists whose collaboration accelerated the pace of discovery.
Chemists Edwin McMillan and Glenn Seaborg became the driving force behind the chemical identification of the new elements. McMillan was the first to synthesize a transuranium element, neptunium (Element 93), in 1940, using the 60-inch cyclotron. Seaborg and his colleagues then took over the work, isolating plutonium and later proposing a major change to the Periodic Table.
Seaborg realized that the transuranium elements were not chemically analogous to the elements above them, but instead formed a new inner transition series. He proposed the “Actinide Concept,” which placed elements 89 through 103 in a separate row, similar to the Lanthanides. This arrangement is now seen in the modern Periodic Table. This conceptual contribution provided a new framework for understanding the behavior of heavy elements.
The legacy of the Berkeley team is reflected in the naming of several elements. Berkelium and Californium honor the city and the state where the research was conducted. Lawrencium recognizes the laboratory’s founder, Ernest Lawrence, and Seaborgium honors Glenn Seaborg.