page_title: Superheavy element
section_title: Decay and detection
hierarchical_section_title: Superheavy element / Introduction / Decay and detection
context_page_description: In chemistry, superheavy elements, also known as transactinide elements, transactinides, or super-heavy elements, are the chemical elements with atomic numbers greater than 103. The superheavy elements are located immediately beyond the actinides in the periodic table; the heaviest actinide is lawrencium. By definition, superheavy elements are also transuranic elements, i.e. having atomic numbers greater than that of uranium.
  Glenn T. Seaborg first proposed the actinide concept, which led to the acceptance of the actinide series. He also proposed a transactinide series ranging from element 104 to 121 and the superactinide series approximately spanning elements 122 to 153. The transactinide seaborgium was named in his honor.
  Superheavy elements are radioactive and have only been obtained synthetically in laboratories. None of these elements have ever been collected in a macroscopic sample. Superheavy elements are all named after physicists and chemists or important locations involved in the synthesis of the elements.
  IUPAC defines an element to exist if its lifetime is longer than 10⁻¹⁴ seconds, which is the time it takes for the nucleus to form an electron cloud.
context_section_description: The beam passes through the target and reaches the next chamber, the separator; if a new nucleus is produced, it is carried with this beam. In the separator, the newly produced nucleus is separated from other nuclides (that of the original beam and any other reaction products) and transferred to a surface-barrier detector, which stops the nucleus. The exact location of the upcoming impact on the detector is marked; also marked are its energy and the time of the arrival. The transfer takes about 10⁻⁶ seconds; in order to be detected, the nucleus must survive this long. The nucleus is recorded again once its decay is registered, and the location, the energy, and the time of the decay are measured.
  Stability of a nucleus is provided by the strong interaction. However, its range is very short; as nuclei become larger, its influence on the outermost nucleons (protons and neutrons) weakens. At the same time, the nucleus is torn apart by electrostatic repulsion between protons, and its range is not limited. Total binding energy provided by the strong interaction increases linearly with the number of nucleons, whereas electrostatic repulsion increases with the square of the atomic number, i.e. the latter grows faster and becomes increasingly important for heavy and superheavy nuclei. Superheavy nuclei are thus theoretically predicted and have so far been observed to predominantly decay via decay modes that are caused by such repulsion: alpha decay and spontaneous fission. Almost all alpha emitters have over 210 nucleons, and the lightest nuclide primarily undergoing spontaneous fission has 238. In both decay modes, nuclei are inhibited from decaying by corresponding energy barriers for each mode, but they can be tunnelled through.
  Alpha particles are commonly produced in radioactive decays because mass of an alpha particle per nucleon is small enough to leave some energy for the alpha particle to be used as kinetic energy to leave the nucleus. Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning. As the atomic number increases, spontaneous fission rapidly becomes more important: spontaneous fission partial half-lives decrease by 23 orders of magnitude from uranium (element 92) to nobelium (element 102), and by 30 orders of magnitude from thorium (element 90) to fermium (element 100). The earlier liquid drop model thus suggested that spontaneous fission would occur nearly instantly due to disappearance of the fission barrier for nuclei with about 280 nucleons. The later nuclear shell model suggested that nuclei with about 300 nucleons would form an island of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half-lives. Subsequent discoveries suggested that the predicted island might be further than originally anticipated; they also showed that nuclei intermediate between the long-lived actinides and the predicted island are deformed, and gain additional stability from shell effects. Experiments on lighter superheavy nuclei, as well as those closer to the expected island, have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.
  Alpha decays are registered by the emitted alpha particles, and the decay products are easy to determine before the actual decay; if such a decay or a series of consecutive decays produces a known nucleus, the original product of a reaction can be easily determined. (That all decays within a decay chain were indeed related to each other is established by the location of these decays, which must be in the same place.) The known nucleus can be recognized by the specific characteristics of decay it undergoes such as decay energy (or more specifically, the kinetic energy of the emitted particle). Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.
  The information available
caption: Scheme of an apparatus for creation of superheavy elements, based on the Dubna Gas-Filled Recoil Separator set up in the Flerov Laboratory of Nuclear Reactions in JINR. The trajectory within the detector and the beam focusing apparatus changes because of a dipole magnet in the former and quadrupole magnets in the latter.[30]