Translated material
Opening elements 113, 115, 117 and 118: what does it give
The opening of new elements of the periodic table of Mendeleev has always aroused interest among the general public. The point is not so much in the scientific significance of these discoveries, but that the school all passed the periodic law, and some even remember the symbols denoting the elements. This is understandable, familiar. But now, these discoveries are complicated research in nuclear physics and radiochemistry, about which many have no idea.
Currently, new elements are obtained only on accelerators of heavy ions. (Previously, they were found in earthly minerals, products of nuclear reactors and nuclear explosions.) Heavy ions accelerated in cyclotons or linear accelerators, bombarded targets of heavy elements, and as a result of a merger reaction with the emission of one or more neutrons, a new element with the ordinal number (the charge of the nucleus) is synthesized - the sum of the charges of the nucleus of the flying Jonah and the kernel of the target. Then the resulting nuclei undergoes radioactive decay. For the synthesis of the most stable isotopes, such combinations of nuclei are chosen, which contain a larger number of neutrons and composite nuclei, have low excitation energy. The output of the resulting heavy elements is extremely small - individual atoms or dozens of atoms, sometimes over the months of irradiation on an accelerator. The half -life period is seconds, and sometimes the share of milliseconds. It is quite difficult to highlight the nuclei of new elements from the entire mixture of the formed nuclear reactions formed and correctly identify the resulting products. For this, special settings are created, which as a result record a chain of decays with the emission of alpha particles and the formation of isotopes of lighter elements, sometimes the chain ends with a spontaneous division of the nucleus.
In our country, since the 1950s, work on the synthesis of new elements on accelerators of heavy ions has been carried out in Dubna under the leadership of Acad. G. N. Fleova (1913–1990) - the founder of this direction. Now these works are carried out under the scientific leadership of Acad. Yu. Ts. Oganesyan. In the world, there are only a few accelerators and installations where you can get transaptinoid elements (i.e., elements with the charge of nucleus z more than 103).
The latest decision by IUPAC (the International Union of Theoretical and Applied Chemistry [1] on the recognition of the discovery of four elements at once-under numbers 113, 115, 117 and 118-attracted the attention of the Russian public also because the priority in three of them-115, 117 and 118-was recognized as the Russian-American collaboration, including the Laboratory of Nuclear Reactions to them. The Institute of Nuclear Research (JIS), Livermother National Laboratory named after E. Lulnl (LLNL), the Oblast National Laboratory (ORNL) and the University of Wanderbilt is recognized as a group of the Japanese accelerating scientific center Riken.
The establishment of priority is a difficult task, since inaccuracies in the first messages about the opening are inevitable to some extent. The question is - what inaccuracies are significant, and which can be accepted and how reasonable the conclusions of the authors are. The IPAC solution was based on the reports of the Joint Working Party, JWP) [2, 3] and previously developed opening criteria. According to existing practice, authors are given the right to propose the name of new elements.
Priority work was published by Flor JIND and Riken almost simultaneously in 2004, a group from Dubna published work even a little earlier. For the synthesis of new nuclei in Japan, a “cold” merger reaction was used, bombarding a zinc isotope from a bismuth of 70zn+209bi, with the formation of an isotope 278113 (life time - milliseconds and tenths of milliseconds).
In Dubna, a more profitable (from the point of view of the output and half-life of the half-life) nuclear reaction of the ions of the heavy isotope of calcium and American 48CA+243am, which leads to the formation of isotopes 288115 and 287115. These radionuclides, emailing alpha parties, are first decomposed, respectively, 284113 and 283113 (lifetime-hundreds of life-hundredths of hundreds of hundreds millisecond), and then along the chain in long -lived isotopes of element 105 (Dubnia, DB). 268DB was distinguished chemically and then recorded spontaneous division.
But intermediate nuclides in these chains of decay at that time were not known, and their independent physical identification was not carried out. And the chemical release and identification of DB based on ion exchange, carried out in the Flor JIS, the combined working group considered non -eellective and unconvincing. Also, attempts were not taken into account to investigate the chemical properties of element 113 by gas chromatography, although this method was previously successfully used to study chemistry of other transaptinoid elements. As a result, it was concluded that the Dubna application in this case does not meet the criteria for opening elements.
At the same time, all the intermediate products of the decay of the Isotope isotope in Japan 278113 (in total 3 events for 8 years of work) were confirmed, including in special experiments in the new research center in heavy Langeo ions in China. Thus, the priority in the opening of element 113 was recognized as the Japanese group.
Element 115 was synthesized in Dubna, and in honor of the region where this international center is located, the authors were proposed by the name Muscovy (Moscovium, MC). The element was again obtained in the 48CA+243AM nuclear reaction with the formation of 287115 and 288115 (life lifetime is tens and hundreds of milliseconds, respectively). Later 289115 and other isotopes of this element were received. Unlike the first cycle of chemical experiments, which the Dubninsky group conducted independently, later, in 2007, the chemical release of the decay product-268DB was already carried out with the involvement of American experts from Livermore, and the belonging of this element-the decay product of the 115th element-to the V group of the periodical system was quite convincingly proved.
Moreover, in 2013, collaborations from the German Center for Research with heavy ions in Darmstadt (GSI) managed to repeat the Dubninsky results on obtaining isotopes of element 115 in a 48CA+243AM nuclear reaction. Thus, the priority in the opening of element 115 was recognized as the Russian-American group.
Element 117 is proposed to name Tennessine (Tennessine, TS) in honor of the American state of Tennessee, where the Okridge National Laboratory is located. The end in the title is the analogy with the astatin and other elements of the halogen group (in English). This element was also synthesized in Dubna, in the 48CA+249BK nuclear reaction. The role of American colleagues from Okridge was mainly in the manufacture of the unique target of Berkli-249, which was received on a high-flow reactor in Ornl. In 2010–2013, only 13 decay chains 293117 and 294117 were recorded, and the characteristics (life and energy of alpha decay) of the decay product 289115 corresponded to the data obtained earlier for this radionuclide in another nuclear reaction 48CA+243AM. For this reason, the application for the opening of this element was recognized as a corresponding criteria.
The element 118 Authors proposed the name Oganeson (Oganesson, OG). It should be an analogue of Radon and other inert gases, and its opening completes the seventh period of the Mendeleev table. This element is proposed to be named in honor of Yuri Tsolakovich Oganesyan for his pioneering contribution to the study of transactinoid elements and important nuclear-physical achievements in the opening of super-heavy nuclei and the study of the “island of nuclear stability”. In history, there was only another example when the name of the element was assigned to the current scientist. Element 106 was named in 1997 Siborgia (SG) in honor of Glenn Silorg (1912–1999), the Nobel Prize laureate, the author of the opening of plutonium and a number of transplutonium elements.
In 2002–2012, in Dubna, when expanding the target of 249CF 48CA, several events of the formation of 294118 were discovered (lifestyle - about 1 millisecond), accompanied by a sequential decay of 290LV (Livermoria), 286FL (Fleurovich) and 282CN (Coppernisia). The lifetime and energy of the alpha particles of these Isotopes FL and CN were confirmed by the American collaboration on the cyclotron in Berkeley, so the united working group recommended recognizing the discovery.
It should be noted that all the newly proposed names and symbols of elements have not yet been approved by IPAC.
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What is the importance of the discovery of these new elements?
The question "How much bread and coal can this give?" Absolutely incorrect. The benefits from the development of a certain branch of fundamental science are often impossible to predict, and such arguments should not inhibit its development. Attempts to describe in advance income and political benefits from scientific discoveries are ridiculous. Considerations of prestige should also not somehow limit the development of the direction, because its true meaning can be revealed much later. Conversely, widely advertised achievements may not have any significant continuation. In general, science should be guided by its logic, and not the logic of people far from it. The society should trust scientists, and “satisfaction of its own curiosity at the state expense” is a normal position in this area of human activity. And it is precisely scientists, qualified specialists should determine what money should be spent on and what can wait or even hopelessly.
Another question is what scientific significance this result can have about the discovery of new elements. What does it change in our ideas about the structure of the nucleus and the chemical properties of elements in general?
From a physical point of view, these results can be important for a better understanding of the nuclear structure and nuclear interaction. Since the 1960s, the issue of the existence of the so-called stability islands in the area of the charges of nuclei z = 114 and 126 as a manifestation of the shell structure of nuclei was violently discussed. Therefore, the receipt of the first transactinoid elements that had a much larger half -life of the old “drip” model of the structure of the nucleus was really fundamentally important. Now no one doubts the shell model. The results obtained by new elements and new isotopes allow you to clarify the existing models of the nucleus and nuclear reactions. Although it is not expected to fundamentally new phenomena, the set of new data is always useful. It is obvious that the peaks of the island of stability cannot be achieved: there are simply no such combinations in nuclear reactions - there are not enough neutrons in the obtained isotopes. Earlier for many years, attempts have been made to detect stae in natural samples that would be so long -lived that they could remain from the time of the formation of the solar system. But these attempts were unsuccessful. The once declared results found neither experimental nor theoretical confirmation.
From a chemical point of view, the situation is somewhat different. Here you can really expect fundamentally new phenomena. The point is the so -called "relativistic effects." In atoms with a large charge of the kernel, electrons acquire relativistic speeds, and the usual Schrödinger equation used to describe atoms is no longer working. In particular, the “dumbbells” of the R-electrons familiar to everyone in the 7th period undergo changes, and one of them turns into a ball. As a result, the electronic structure of atoms changes. In new elements, a significant deviation of the chemical properties from extrapolated according to the periodic table and the emergence of unusual chemical properties is possible.
In relation to “relativistic effects” there are many speculations obviously aimed at raising interest in the issue. For example, it was suggested that the element 104 of Rutherfordi (RF)-a formal analogue of titanium, zirconium and gafnia-may turn out to be a P-element, in chemical properties close to lead. Or it was stated that the element 114 of the Fleroviy (FL) - an analogue of lead - may turn out to be inert gas. In fact, upon neat consideration, it turns out that although the RF atom has an unusual configuration of the external electronic shell (DS2P), according to its chemical properties, this is a typical D-element, an analogue of Gafnia. And FL, having increased volatility (as follows from any extrapolations), in a condensed state remains a typical metal. In general, it is absolutely incorrect that any deviation from extrapolation according to the periodic system attributes to “relativistic effects”: it can be due to completely different causes, for example, intercontigation interaction.
One way or another, the study of relativistic effects allows you to better understand the chemical properties of long -known and widespread elements. This also allows you to better understand how the electronic structure of atoms and molecules that can be calculated determines their specific chemical properties. This is still far from fully resolved. Further advance on the periodical table can lead to the formation of a completely new group of elements-G-elements (starting with element 121) with interesting properties. All these issues are still waiting for a detailed study.
However, it has to be noted that in the latest discoveries the chemical properties of new elements do not appear at all (only the product of the decay of element 115 - element 105, DB was chemically distinguished to confirm the end of the collapse chain). But such a study was difficult to conduct due to a low exit and short periods of half -life of the received isotopes. Nevertheless, this is possible, although it requires a new approach to the production of chemical experiments.
The discovery of new elements gives another example of the fact that significant achievements of Russian scientists are possible in close collaboration with scientists from the USA, Germany and other developed countries. It is such works that raise the prestige of our science.
- International Union of Pure and Applied Chemistry. Official site: http://iupac.org/
- Karola Pj, Barber RC, Sherrill V. M., Vardaci E., Yamazaki T. Discovery of the Elements with Atomic Numbers Z = 113, 115 and 117 (IUPAC Technical Report) // Pure Appl. Chem. 2016. V. 88. P. 139–153.
- Karola Pj, Barber RC, Sherrill BM, Vardaci E., Yamazaki T. Discovery of the Elements with Atomic Numbers Z = 118 (IPAC Technical Report) // Pure Appl. 2016. V. 88. P. 155–160.
- Hamilton H., Hofman S., Oganessian Yt Search for Superheavy Nuclei // Annu. Rev. NUCL. Part. SCI., 2013. V. 63. P. 383–405.