Hassium

Hassium is a synthetic chemical element with the symbol Hs and atomic number 108. Because it is created in laboratories rather than found in nature, it is classified as a superheavy element. Scientists have hypothesized that hassium might occur naturally, but no such occurrences have ever been found. In the periodic table, hassium is a transactinide element located in period 7 and group 8. This placement makes it the sixth member of the 6d series of transition metals.

Chemists have studied how hassium behaves by comparing it to its heavier homologue, osmium. Experiments confirm that hassium reacts readily with oxygen to form a volatile tetroxide. While its full chemical properties are only partly characterized, they align well with other group 8 elements. Hassium is also highly radioactive. Its most stable known isotopes have half-lives of approximately ten seconds. One specific isotope of hassium possesses magic numbers of protons and neutrons for deformed nuclei. This unique structure provides greater stability against spontaneous fission, which is when a nucleus splits apart.

Creating hassium requires a specialized process known as cold fusion. In earlier nuclear reactions from the 1960s, scientists used a method called hot fusion. This involved hitting targets with high atomic numbers to maximize the size difference between nuclei. While this increased the chance of fusion, the resulting compound nuclei often had high excitation energy. These unstable nuclei would eject four or five neutrons to reach a stable state. This process often left the final products neutron-poor and very short-lived.

To solve this, physicist Yuri Oganessian proposed the cold fusion mechanism at the Joint Institute for Nuclear Research (JINR). This method uses a target nucleus like lead-208, which possesses magic numbers of protons and neutrons. These magic numbers mean more of the nucleus's rest energy is diverted to binding the nucleons together. This extra binding energy makes the target nucleus much more stable. Because the target is so stable, it requires less energy to penetrate it. This results in lower excitation energy for the new compound nucleus. Consequently, fewer neutrons are ejected during synthesis, creating heavier and more stable nuclei.

The history of discovering hassium involves several years of intense research and competing claims. The JINR in Dubna, Soviet Union, first tested cold fusion in 1974. Researchers there attempted to synthesize element 108 in 1978, 1983, and 1984. In 1978, they used radium and calcium to attempt the reaction, but the data was not unambiguous. In 1984, JINR researchers recorded twenty-one spontaneous fission events that they believed were caused by element 108. However, a separate team at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, West Germany, also reported a successful synthesis in 1984. The GSI team bombarded a lead target with accelerated iron nuclei.

Because two different groups claimed discovery, an arbitration process was necessary. The International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) formed the Transfermium Working Group (TWG). This group assessed the evidence from both the Soviet and German laboratories. In a 1993 report, the TWG concluded that the GSI work was conclusive on its own. While they noted the JINR work "very probably" showed synthesis, the GSI work clearly identified the specific decay path. Therefore, the major credit for the discovery was assigned to the German scientists. Both JINR and GSI eventually agreed with this decision.

Naming the element followed specific scientific regulations. While discoverers traditionally propose names, they must be approved by IUPAC. Before a permanent name was chosen, the element was referred to by several placeholders. Scientists used "element 108," the symbol "E108," or the systematic name "unniloctium." In older nomenclature, it might have been called "eka-osmium." Ultimately, GSI chose to name the element hassium to honor the German state of Hesse. This name is derived from the Latin name for Hesse, Hassia. The name was officially accepted as final in 1997.