During the operation of the Superheavy Element Factory (SHE) at the Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in 2020-2022, five new isotopes of superheavy elements were obtained for the first time in the world: 264 Lr, 286 Mc, 276 Ds, 272 Hs and 268 Sg. The fact that several previously unknown isotopes were discovered at the same time during the two years of the Factory’s operation indicates that this is an advanced research facility that sets new standards in the field of synthesis and study of the properties of superheavy elements.
Lawrencium-264 was obtained during the first experiments at the SHE Factory on the synthesis of moscovium isotopes in the reaction 48 Ca+ 243 Am. The lifetime of the new nuclide was about five hours. This experiment repeated the reactions that had already been studied earlier, and not only at FLNR, but also at scientific centers in Germany, Japan, and the USA.
“In the very first experiment, in these seemingly well-known and well-studied reactions, we saw a new isotope of lawrencium-264. For us, this was an indicator that the Superheavy Element Factory really works as intended and surpasses the facilities of the previous generation in its capabilities,” commented Alexander Karpov, FLNR Scientific Secretary JINR. He added that the most important factor in the discovery of lawrencium-264 was the good background conditions in the focal plane of the Factory’s first separator, DGFRS-II (Dubna Gas-Filled Recoil Separator), which is able to filter out non-fusion events extremely effectively. superheavy elements. According to the scientist, it was previously believed that the decay of moscovium-288 follows a chain of several alpha decays and ends with the spontaneous fission of dubnium-268, in about a day. However, FLNR scientists managed to establish that in almost half of the cases, dubnium actually fissions, and in the remaining ~50% of cases, it emits an alpha particle, forming lawrencium-264, which had not been observed before. About 50 formation events were recorded264 Lr out of 110 events 288 Mc.
Another strong point of the STE Factory is its high performance, which allows you to collect statistics much faster. Thus, it is sometimes possible to study a reaction at several beam energies in one experiment, while working with extremely low fusion cross sections (probabilities), which makes it possible to obtain completely new information. So, in 2021, one event of the formation of a new isotope, moscovium-286, whose lifetime is only 20 milliseconds, was received at the SHE Factory. “We were able to detect this isotope precisely due to the fact that statistics are now accumulating many times faster than before,” said Alexander Karpov.
The 2022 experiment used a reaction that has not yet been studied anywhere in the world – the interaction of a calcium-48 beam with a thorium-232 target material. In this combination, three previously unknown isotopes were obtained at once: darmstadtium-276 (six events), hassium-272 and seaborgium-268 (two events each). It turned out that darmstadium-276 undergoes alpha decay in a fraction of a millisecond into hassium-272, and hassium, in turn, undergoes alpha decay in a hundred milliseconds into seaborgium-268, which spontaneously divides within 10-15 seconds.
The main purpose of this experiment is to prepare for the synthesis of the 120th element of the Periodic Table. Theory predicts that a minimum cross section was expected for the calcium–thorium reaction. The cross sections in the reaction with calcium-48 increase both when moving to lighter elements and to heavier ones. And for the 110th element, darmstadtium, its minimum was predicted by theory. “To try to synthesize a nucleus at the Factory, for which the expected survival rate is even lower than for the 120th element, was very important in order to demonstrate that we can conduct experiments with very low cross sections. Below what we have worked so far. And this was also achieved, ”explained Alexander Karpov.
The second circumstance on which it was important to conduct a study is that the isotopes of the 120th element, which can be obtained in one of the possible fusion reactions, will pass through the decay chain through darmstadtium-276, hassium-272 and seaborgium-268. “Therefore, it was very important to obtain these nuclei separately, to study their properties, so that later, when observing the fusion events of the 120th, we would have a firm conviction that we would correctly identify the nuclei,” said Alexander Karpov.
In the spring of 2023, FLNR JINR plans to continue the study of the calcium-thorium reaction, but at a higher beam energy. One can hope both to refine the properties of the newly discovered darmstadtium-276, and to synthesize other, as yet unknown, isotopes of this element, namely darmstadtium-275 or darmstadtium-274.
“Over two years of work, we were able to obtain as many as five new isotopes, which indicates that the SHE Factory is indeed an extra-class complex for the synthesis and study of superheavy elements,” the FLNR Scientific Secretary emphasized. The parameters of both the accelerator and the Fabrika separators were initially adapted for the most efficient solution of problems in the field of physics and chemistry of superheavy elements. “This accelerator complex is invested with all our experience in the creation of accelerators and separators, which has been accumulated over the previous decades, taking into account all the ideas for improving the parameters of the facilities. In fact, we gave everything 100 percent,” said Alexander Karpov.
Another advantage of the specialized complex is that FLNR JINR scientists have the opportunity to work on it almost all year round, while the time of sessions at accelerator complexes in other scientific centers has to be divided between research groups working in different directions. “We have an advantage both in time and in access to the target and beam forming material. The accelerator complex of the Factory of Superheavy Elements is now truly the leader in the world in all respects,” summed up Alexander Karpov.
