Superheavy element

Superheavy elements are chemical elements with an atomic number of 104 or higher. They are also known as transactinide elements because they appear beyond the actinide series in the periodic table. The last element in the actinide series is lawrencium, which has an atomic number of 103. Because these elements have atomic numbers greater than uranium, which is 92, they are also classified as transuranium elements. These elements are not found in nature and must be created synthetically in laboratories. They are all radioactive, meaning their nuclei are unstable and will eventually decay.

To create a superheavy nucleus, scientists use a process called nuclear fusion. This involves combining two nuclei of unequal size into a single new nucleus. Researchers create a target made of heavier nuclei and bombard it with a beam of lighter nuclei. Because all nuclei are positively charged, they naturally repel each other due to electrostatic repulsion. To overcome this, the beam nuclei are accelerated to incredible speeds. They can reach velocities as high as one-tenth of the speed of light. If the nuclei approach closely enough, the strong interaction can overcome the repulsion and pull them together.

Even when nuclei approach, they often fail to fuse immediately. They may stay together for about 10 seconds before electrostatic repulsion tears them apart. For a successful merger, the nuclei must reach an energy equilibrium. This creates a temporary, highly unstable state called a compound nucleus. To become more stable, this compound nucleus might undergo fission, which means it splits apart. Alternatively, it may eject a few neutrons to carry away excess excitation energy. If neutron expulsion is not enough, the merger might produce a gamma ray. This process typically happens within 10 seconds of the initial collision.

Detecting these elements requires very precise equipment. After the collision, the beam passes through a device called a separator. This separator pulls the newly produced nucleus away from the original beam and other reaction products. The nucleus is then transferred to a surface-barrier detector, a process that takes about 10 seconds. This timing is critical because the IUPAC defines an element as existing only if its lifetime exceeds 10 seconds. This duration is the time required for a nucleus to form an electron cloud. Once the nucleus hits the detector, scientists record its exact location, energy, and arrival time.

Scientific history shows a long period of predicting these massive atoms. At the end of the 19th century, uranium was the heaviest known element. In 1895, Danish chemist Julius Thomsen proposed the existence of heavy noble gases. In 1913, Swedish physicist Johannes Rydberg extrapolated the periodic table up to an atomic number of 460. He believed these elements did not exist in nature. Later, in 1926, Richard Swinne suggested they might be found in cosmic rays. He even speculated they could be hidden in the Earth's core or Greenland's ice caps. Since 1961, various laboratories have worked to turn these theories into reality.

Superheavy nuclei face a constant struggle between two physical forces. The strong interaction provides stability, but it has a very short range. As nuclei get larger, this force weakens for the outermost protons and neutrons. Meanwhile, electrostatic repulsion has a much longer range and grows stronger as the atomic number increases. This imbalance causes most superheavy isotopes to decay quickly, often with half-lives of minutes or less. They primarily decay through alpha decay or spontaneous fission. In alpha decay, the nucleus emits alpha particles to lose mass. In spontaneous fission, the nucleus is torn apart by the intense electrical repulsion between protons.

Physicists are currently searching for a theoretical region called the "island of stability." According to the nuclear shell model, certain numbers of nucleons might create more stable nuclei. These nuclei would be more resistant to spontaneous fission and might have longer half-lives. While earlier models suggested this island might occur around 280 nucleons, newer discoveries suggest it may be further away. Some intermediate nuclei show more stability than expected due to shell effects. Understanding these shell effects helps scientists predict how the heaviest elements in the universe might behave.