日本理化研究所发现第113号元素

Element 113, discovered by a RIKEN group led by Kosuke Morita, has become the first element on the periodic table found in Asia. Rewarding nearly a decade of painstaking¹ work by Morita's group, a Joint² Working Party of the International Union of Pure and Applied³ Chemistry (IUPAC) and International Union of Pure and Applied Physics (IUPAP) has recommended that the group, from the RIKEN Nishina Center for Accelerator-based Science (RNC), be given recognition for the discovery of the new element. This news was conveyed to Dr. Morita through a letter on Dec. 31, 2015, from IUPAC. In the late 1980s, the group began using RIKEN's Linear Accelerator Facility and the GARIS ion separator, developed by Morita and his group, to explore new synthetic⁴ superheavy elements. The work of discovering new superheavy elements is very difficult, and the elements tend to decay extremely quickly -- the isotopes⁵ of 113 produced at RIKEN lasted for less than a thousandth of a second. Researchers persevere⁶, however, as the research is important for understanding the structure of atomic nuclei⁷. Scientists hope that the work will lead eventually to the discovery of a so-called "island of stability" where elements with longer half-lives will be found.

 

The search at RIKEN for element 113 started in September 2003, when Morita's group began bombarding a thin layer of bismuth with zinc⁸ ions travelling at about 10% the speed of light. Theoretically, they would occasionally fuse, forming an atom of element 113.

 

The team achieved its first success on July 23, 2004, less than a year after starting the experiment. Two atomic nuclei fused, leading to the creation of a nucleus⁹ of element 113, which quickly underwent four alpha decays to transform into dubnium-262 (element 105), which then underwent spontaneous fission¹⁰. Less than a year later, on April 2, 2005, the team saw a second event -- an identical decay to dubnium-262 followed by fission. Though these were good demonstrations¹¹, they were not considered conclusive¹² evidence for the existence of element 113, because the decay chain did not demonstrate 'firm connections to known nuclides' (according to the Joint Working Party's 2011 report). The team pushed on with its efforts.

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