in your element The making of moscovium Yuri Oganessian relates the story of the formation and decay of a doubly odd moscovium nucleus.
lement 115 was the first superheavy of the nucleus by two, and we move element with an odd atomic 288 away by two neutrons from the magic 115Mc Enumber (Z) that we synthesized number N = 184. As a result, the nucleus in nuclear reactions using a beam of becomes more stable to alpha decay, 284Nh accelerated 48Ca ions. These experiments 113 but more prone to spontaneous fission were carried out in 2003, on the heels and eventually the chain will be of the first results obtained for even 280 terminated by spontaneous fission. 111Rg elements 114 and 116. We had no At what point will this happen? Only
doubts that their odd neighbour 276 experiments will tell. could also be produced in a similar 109Mt In our 2003 experiments, detectors manner; its decay properties however allowed us to document the entire 272 would be very different. 107Bh radioactive family of the nuclei formed, The target isotope 243Am (Z = 95) was and to determine the energy and time of 48 bombarded with ions of Ca (Z = 20) in 268 emission of each alpha particle emitted the hope that a rare process — the fusion 105Dbb as well as the energy of the fragments of 268Rf of these nuclei — would occur. A 291115 104 spontaneous fission. The decay chain of the nucleus did indeed form. During 288115 isotope obtained is pictured. After five the process this nucleus was heated consecutive alpha transitions within the first Credit: Loop Images Ltd / Alamy Stock Photo (to around 4×1011 K), and cooled down 20 seconds, there was a long pause, which through the very fast emission of three brought us a lot of trouble. Spontaneous neutrons, and gamma rays, to form fission of the last nucleus in the chain — the the isotope 288115. The thickness of the isotope 268Db — was registered only the next americium target was chosen so that its probability rises rapidly with increasing day, after 30–40 hours. We think that the once made, the 288115 nucleus, with the atomic number. According to the classic isotope 268Db (Z = 105, N = 163) decayed recoil energy obtained in collision, can (macroscopic) nuclear theory, spontaneous through electron capture to give an even– escape out of the target. Its time of flight fission sets the limit of elements that can even 268Rf nucleus (Z = 104, N = 164), which on the 4-metre path from the target to exist at Z = 100 (fermium). then quickly divided into two fragments. the detector through the separator is only In 1969 a new (microscopic) theory In our first experiments we detected a total about one microsecond. The separator was devised that takes into account of three such events. Since then, a similar was configured and tuned to allow the the structure of nuclear matter, giving picture of the decay of element 115 has superheavy nuclei formed to pass through, different predictions: stability is expected to been observed over a hundred times in yet sweep away all the lighter by-products increase again in the domain of very heavy, Dubna (Russia), Darmstadt (Germany) and of the reaction from the main trajectory. neutron-rich nuclei (with mass numbers Berkeley (United States). The atoms of interest reach the detector around 280–300). Near ‘magic’ numbers The name we proposed for element assembly, enabling the detection of of protons and neutrons, Z = 114 and 115, located in the periodic table at the nuclei formed by determination of their N = 184, a vast area of relatively stable bottom of group 15 under bismuth, was decay patterns. elements appears in the periodic table adopted: ‘moscovium’, in honour of the Two types of radioactive decay compete that is dubbed the island of stability; ancient Russian land of Moscovia, the in superheavy elements: alpha-decay element 115 is one of these. Additionally, the Moscow region where the people who first and spontaneous fission. The former, internal structure of the 288115 nucleus — produced it and observed its spontaneous discovered by Henri Becquerel in 1898, with odd numbers of protons and neutrons transmutation into other elements lived is the spontaneous emission of an alpha (Z = 115, N = 173) — largely prevents and worked. ❐ particle (4He) by a heavy nucleus; it is typical spontaneous fission, so it is likely that the of many nuclei heavier than lead. The latter, nucleus will undergo alpha decay. Yuri Oganessian in which a nucleus splits into two fragments, Emission of an alpha particle forms an Flerov Laboratory of Nuclear Reactions, was discovered by Georgy Flerov and odd–odd nucleus of the element 113 that, Joint Institute for Nuclear Research, Dubna, Konstantin Petrjak in 1940. It is observed for the same reasons, will also undergo alpha Moscow region, Russia. only for actinides and transactinides, and decay. This decay pattern is reproduced e-mail: [email protected] with the element 111, then 109, and so on. At each step of this odd–odd Published online: 14 December 2018 stairway we decrease the atomic number https://doi.org/10.1038/s41557-018-0185-6
Cn Nh Fl Mc Lv Ts Og 119 120 121 122 123 124 125 126 127 128 129 130 131 132
98 Nature Chemistry | VOL 11 | JANUARY 2019 | 98 | www.nature.com/naturechemistry