An innovative way of producing superheavy elements may soon add a new row to the periodic table, allowing scientists to explore the uncharted atomic realm.
Usually, newly synthesized, artificially manufactured heavy elements on the periodic table are too “gigantic”, often leading to their instability and fleeting existence. Scientists have been striving to compress more protons and neutrons together to construct “superheavy” atomic nuclei – nuclei with a total of protons exceeding 103 – making such elements increasingly unstable.
So far, all superheavy elements created by humans have almost instantly decayed. However, researchers at the Lawrence Berkeley National Laboratory in the United States have taken a significant step towards the mysterious “island of stability” by synthesizing these heavy elements using a particle accelerator.
The “island of stability” is a theoretical area in nuclear physics where superheavy elements may finally be able to exist stably, breaking the norm.
The team successfully synthesized the element with atomic number 116, livermorium, using a new method that utilized titanium-50, a rare isotope accounting for about 5% of all titanium on Earth. By heating this titanium to 3,000 degrees Fahrenheit and converting it into a high-energy particle beam, researchers were able to collide this beam with other atoms to create superheavy elements.
Although livermorium had been previously produced using other methods, this innovative approach paved the way for synthesizing new, heavier elements, potentially expanding the periodic table.
“This achievement is truly groundbreaking,” said Hiromitsu Haba, a researcher at the RIKEN institute in Japan who was not involved in the study. He also noted that this achievement is a “necessary condition for further discovery of new elements.” The research results have been presented at the Nuclear Structure conference in July and are currently undergoing peer review in the journal Physical Review Letters.
The 88-inch Cyclotron at Berkeley Lab is a device capable of generating electromagnetic fields, propelling atomic nuclei to release some peripheral electrons and speeding them to collide with other stationary atoms. Through these devices, the process of synthesizing superheavy elements becomes a simple mathematical problem: to create an element with 116 protons, you need to fuse two nuclei to achieve this total number of protons. However, in the field of nuclear physics, things are often not so straightforward.
Traditionally, calcium-48 has been the preferred isotope for fusion reactions to create superheavy elements due to its “doubly magic nature”. Atomic nuclei are surrounded by shells made up of electron orbits; when a nucleus possesses the “magic” protons or neutrons needed to completely fill a shell orbit, they become highly stable, and having both types of particles in a “doubly magic” state enhances stability even further. However, calcium-48 has a lower number of protons, limiting its ability to synthesize heavier elements.
The heaviest stable element that can combine with calcium-48 (20 protons) is curium (96 protons), ultimately forming livermorium (116 protons). While calcium-48 and heavier berkelium (97 protons) have been used to synthesize element 117, berkelium is “extremely difficult to manufacture.” Witold Nazarewicz, Chief Scientist at the Rare Isotope Beam Facility at Michigan State University who was not involved in the new study, said, “If we want to produce more and heavier elements, we need a particle beam with more protons than calcium-48.”
To create such a particle beam, the research team turned to titanium-50, attempting to fuse it with plutonium to produce livermorium. “No one knew before conducting this experiment whether using titanium to create matter would be easy or difficult,” emphasized Jacklyn Gates, head of the Heavy Element Group at Berkeley Lab and the lead author of the study.
Unlike the highly stable “doubly magic” calcium-48, titanium-50 does not possess magical properties and lacks extreme stability. Its melting point is nearly twice that of calcium, making it more challenging to handle. The lower stability of titanium-50 makes it difficult to successfully fuse even upon collision. “It’s like seeing a synthetic atom every day versus once every ten days or even longer,” Gates explained. Despite these challenges, titanium-50 is seen as the next best choice because it offers possibilities beyond what calcium can achieve in creating superheavy elements.
When the isotopes are prepared and the cyclotron begins operating, the next step is a long wait. Continuously aiming the titanium particle beam at a uranium target for collisions, the probability of any collision between the two nuclei is extremely low. “If you were to enlarge an atom to the size of a football field, the nucleus would be like a pea,” Gates said. “We shoot sixty trillion titanium particles per second at the target just to have a chance to collide with the nucleus.”
The high-intensity particle bombardment and rarity of successful collisions lead to the synthesis of measurable livermorium taking 22 days.
The successful application of titanium-50 in the field of superheavy element synthesis marks significant progress. This experiment not only proves the technology is fundamentally feasible but also provides crucial data on the “cross-section” of the titanium-50 particle beam (the probability of a specific outcome occurring in a collision based on the collision energy).
Building on this foundation, the next ambitious goal is to use titanium-50 for fusion to create element 120, which requires colliding with californium. Element 120 will become the heaviest element synthesized to date and the first element in the eighth row of the periodic table. According to some models, this element should also have a relatively longer half-life, becoming the starting point for the long sought-after “island of stability”. While theoretical models offer little certainty about the precise energy needed for titanium-based synthesis, these preliminary results provide valuable insights.
“Experimental data on the cross-section have been obtained, and now we know which (theoretical) model is the most reliable,” explained Nazarewicz. Hiromitsu Haba added, “We are exploring atomic nuclei in extreme environments, which are still difficult to predict theoretically… However, we have no reason to believe that element 120 cannot be synthesized using this method.”
Although creating this new element may take several more years, this potential discovery is poised to offer new insights into electron shell configurations and the periodic table, which could have significant implications for nuclear physics, material science, and other fields. “You’re going into the ‘g’ orbitals (of electrons),” Gates said, referring to a theoretically new electron configuration that is unprecedented. “It’s like opening up a whole new realm of chemistry.” ◇