Hasio

Hasium is a synthetic element of the periodic table whose symbol is Hs and its atomic number is 108. Its most stable isotope is Hs-269, which has a half-life of 9.7 seconds.

History

Hasium was first synthesized in 1984 by the German research group Gesellschaft für Schwerionenforschung located in Darmstadt. The name hasio proposed by the group is due to the German state of Hesse in which the GSI is located.

There was controversy over the naming of elements 101 to 109. Initially IUPAC adopted the name unniloctio (from symbol One) as a temporary and systematic name for this element. In 1994, IUPAC recommended the name hahnium for element 108, but the name hassio was finally adopted internationally in 1997. In 2017, Spanish naming bodies eliminated the graphic sequence —ss—, even as a variant, because it is foreign to the Spanish orthographic system.

Discovery

Cold Fusion

The nuclear reactions used in the 1960s gave rise to high excitation energies that required the ejection of four or five neutrons; these reactions used targets made of elements with high atomic numbers to maximize the difference in size between the two nuclei in a reaction. Although this increased the chances of fusion due to less electrostatic repulsion between the target and the projectile, the composite nuclei formed often broke apart and did not survive to form a new element. Furthermore, fusion processes inevitably produce neutron-poor nuclei, as heavier elements require more neutrons per proton to maximize stability; therefore, the necessary neutron ejection results in final products that often have lifetimes. shorter. Therefore, the light beams (six to ten protons) allowed the synthesis of elements only up to 106.

To move towards heavier elements, Soviet physicist Yuri Oganessian at the Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, proposed a different mechanism, in which the bombarded nucleus would be lead-208, which has a magic number of protons and neutrons, or another nucleus close to it. Each proton and neutron has a fixed value of rest energy; those of all protons are the same and so are those of all neutrons. In a nucleus, part of this energy is diverted to the union of protons and neutrons; if a nucleus has a magic number of protons and/or neutrons, then it deviates further from its rest energy, giving the nuclide additional stability. This added stability requires more energy for an outer core to break through the existing one and penetrate it.

More energy diverted to the binding of nucleons means less rest energy, which in turn means less mass (mass is proportional to rest energy). More equal atomic numbers of the reacting nuclei give rise to greater electrostatic repulsion between them, but the lower excess mass of the target nucleus balances this out. This leaves less excitation energy for the newly created compound nucleus, which needs fewer ejections of energy. neutrons to reach a steady state. Due to this energetic difference, the first mechanism is known as "hot fusion" and the second as "cold fusion".

Cold fusion was first declared successful in 1974 at JINR, when it was tested for the synthesis of the as yet undiscovered element 106. These new nuclei were projected to decay by spontaneous fission. The JINR physicists concluded that element 106 was produced in the experiment because no fission nuclei known at the time showed fission parameters similar to those observed during the experiment and because changing either nuclei in the reactions nullified the effects. observed. Physicists at the Lawrence Berkeley Laboratory (LBL; originally Radiation Laboratory, RL, and later Lawrence Berkeley National Laboratory, LBNL) at the University of California at Berkeley, United States, also expressed great interest in the new technique. How far could this new method go and if the lead targets were a Klondike of physics, Oganessian replied: "Klondike may be an exaggeration [...] But soon, we will try to get elements 107... 108 in these reactions".

Reports

The synthesis of element 108 was initially attempted in 1978 by the group of researchers led by Oganessian at the JINR. The group used a reaction that could generate element 108, specifically, the ²⁷⁰108 isotope, from the fusion of radium (specifically, the 226
88Ra) and calcium (48
20Ca). The researchers were uncertain about how to interpret the data, and their report did not clearly state a claim that they had discovered the element. That same year, another group of researchers at JINR investigated the possibility of synthesizing element 108 from chemical reactions. between lead (208
82Pb) and iron (58
26Fe); they were uncertain about how to interpret the results, indicating that it was possible that element 108 had not been created.

Linear GSI particle accelerator UNILAC, where hasium was discovered and where its chemistry was first observed

In 1983, new experiments were performed at JINR. The experiments likely resulted in the synthesis of element 108; bismuth (209
83Bi) was bombarded with manganese (55
25Mr) to get ²⁶³108, lead (207
82Pb, 208
82Pb) was bombarded with iron (58
26Fe) to get ²⁶⁴108, and californio (249
98Cf) was bombed with neon (22
10Ne) to get ²⁷⁰108.These experiments were not heralded as a discovery. to and Oganessian announced them at a conference rather than through a written report.

In 1984, researchers at the JINR in Dubna carried out experiments with identical schemes to those carried out previously; they bombarded bismuth and lead targets with ions of the lighter elements manganese and iron, respectively. Twenty-one spontaneous fission events were recorded; the researchers concluded that they had been caused by ²⁶⁴108.

Arbitration

In 1985, the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) formed the Transfer Working Group (TTG) to evaluate the discovery and establish definitive names for the elements with atomic numbers greater than 100. The group held meetings with delegates from the three competing institutes; in 1990, they established the criteria for the recognition of an element and in 1991, they finished the work of evaluating the discoveries and dissolved. These results were published in 1993.

According to the report, the 1984 work by the JINR and the GSI simultaneously and independently established the synthesis of element 108. Of the two 1984 papers, the GSI work was considered sufficient as a discovery on its own. The JINR work, which preceded that of the GSI, showed "very likely" the synthesis of element 108. However, this was determined in hindsight given the Darmstadt work; the JINR work focused on chemically identifying the remote granddaughters of the element 108 isotopes (which could not exclude the possibility that these daughter isotopes had other parents), while the GSI work clearly identified the decay trajectory of those isotopes of element{nbs}}108. The report concluded that the greatest credit should be given to the GSI. In their written responses to this opinion, both the JINR and the GSI concurred with its conclusions. In the same response, GSI confirmed that they and the JINR had been able to resolve all conflicts between them.

Additional bibliography

• Audi, G.; Kondev, F. G.; Wang, M. et al. (2017). «The NUBASE2016 evaluation of nuclear properties». Chinese Physics C (in English) 41 (3): 30001. Bibcode:2017ChPhC..41c0001A. S2CID 126750783. doi:10.1088/1674-1137/41/3/030001. Archived from the original on August 1, 2020.
• Beiser, A. (2003). Concepts of modern physics (in English) (6th edition). McGraw-Hill. ISBN 978-0-07-2448-1. OCLC 48965418.
• Greenwood, N.N.; Earnshaw, A. (1997). Chemistry of the Elements (in English) (2nd edition). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
• Hoffman, D.C.; Ghiorso, A.; Seaborg, G.T. (2000). The Transuranium People: The Inside Story (in English). World Scientific. ISBN 978-1-78-326244-1.
• Hoffman, D.C.; Lee, D.M.; Pershina, V. (2006). "Transactinides and the future elements". In Morss, L.R.; Edelstein, N.M.; Fuger, J., eds. The Chemistry of the Actinide and Transactinide Elements (in English) (3rd edition). Springer Science+Business Media. pp. 1652-1752. ISBN 978-1-4020-3555-5.
• Kragh, H. (2018). From Transuranic to Superheavy Elements: A Story of Dispute and Creation (in English). Springer. ISBN 978-319-75813-8.
• Lide, D. R. (2004). Handbook of chemistry and physics (in English) (84th edition). CRC Press. ISBN 978-0-8493-0566-5. (requires registration).
• Zagrebaev, V.; Karpov, A.; Greiner, W. (2013). «Future of superheavy element research: Which nuclei could be synthesized within the next few years?». Journal of Physics: Conference Series (in English) 420 (1): 012001. Bibcode:2013JPhCS.420a2001Z. ISSN 1742-6588. S2CID 55434734. arXiv:1207.5700. doi:10.1088/1742-6596/420/1/012001.