By the end of the 60s, through the efforts of many theorists - O. Bohr and B. Motelson (Denmark), S. Nilsson (Sweden), V.M. Strutinsky and V.V. Pashkevich (USSR), H. Myers and V. Svyatetsky (USA), A. Sobichevsky and others (Poland), W. Greiner and others (Germany), R. Nix and P. Möller (USA), J. Berger (France) and many others created the microscopic theory of atomic nuclei. The new theory brought all the above contradictions into a harmonious system of physical laws.
Like any theory, it had a certain predictive power, in particular in predicting the properties of very heavy, still unknown nuclei. It turned out that the stabilizing effect of nuclear shells will work beyond those indicated by the droplet model of the nucleus (i.e. in the region Z > 106) forming the so-called. “islands of stability” around the magic numbers Z=108, N=162 and Z=114, N=184. As can be seen in Fig. 2, the lifetime of superheavy nuclei located in these “islands of stability” can increase significantly. This especially applies to the heaviest, superheavy elements, where the effect of closed shells Z=114 (possibly 120) and N=184 increases half-lives to tens, hundreds of thousands and, perhaps, millions of years, i.e. - 32-35 orders of magnitude more than in the absence of the effect of nuclear shells. This is how an intriguing hypothesis arose about the possible existence of superheavy elements, significantly expanding the boundaries of the material world. A direct test of theoretical predictions would be the synthesis of superheavy nuclides and the determination of their decay properties. Therefore, we will have to briefly consider the key issues associated with the artificial synthesis of elements.

2. Synthesis reactions of heavy elements

Elements heavier than Pm (Z=100) were synthesized in reactions with accelerated heavy ions, when a complex of protons and neutrons is introduced into the target nucleus. But this type of reaction is different from the previous case. When a neutron that does not have an electric charge is captured, the excitation energy of the new nucleus is only 6 - 8 MeV. In contrast, when target nuclei merge even with light ions such as helium (4 He) or carbon (12 C), heavy nuclei will be heated to an energy E x = 20 - 40 MeV. With a further increase in the atomic number of the projectile nucleus, it will need to impart more and more energy to overcome the electrical forces of repulsion of positively charged nuclei (the Coulomb reaction barrier). This circumstance leads to an increase in the excitation energy (heating) of the compound nucleus formed after the merger of two nuclei - the projectile and the target. Its cooling (transition to the ground state E x = 0) will occur through the emission of neutrons and gamma rays. And here the first obstacle arises.

A heated heavy nucleus will be able to emit a neutron only in 1/100th of cases; basically, it will split into two fragments because the energy of the nucleus is significantly higher than the height of its fission barrier. It is easy to understand that increasing the excitation energy of a compound nucleus is detrimental to it. The probability of survival of a heated nucleus drops sharply with increasing temperature (or energy E x) due to an increase in the number of evaporated neutrons, with which fission strongly competes. In order to cool a nucleus heated to an energy of about 40 MeV, it is necessary to evaporate 4 or 5 neutrons. Each time fission will compete with the emission of a neutron, as a result of which the probability of survival will be only (1/100) 4-5 = 10 -8 -10 -10. The situation is complicated by the fact that as the temperature of the core increases, the stabilizing effect of the shells decreases, therefore the height of the fission barrier decreases and the fission of the core increases sharply. Both of these factors lead to an extremely low probability of the formation of superheavy nuclides.

Advancement into the region of elements heavier than 106 became possible after the discovery in 1974 of the so-called. cold fusion reactions. In these reactions, “magic” nuclei of stable isotopes are used as target material - 208 Pb (Z = 82, N = 126) or 209 Bi (Z = 83, N = 126), which are bombarded by ions heavier than argon (Yu.Ts. Oganesyan , A.G. Demin, etc.). During the fusion process, the high binding energy of nucleons in the “magic” target nucleus leads to the absorption of energy during the rearrangement of two interacting nuclei
into a heavy core of total mass. This difference in the “packing” energies of nucleons in the interacting nuclei and in the final nucleus largely compensates for the energy required to overcome the high Coulomb barrier for the reaction. As a result, a heavy nucleus has an excitation energy of only 12-20 MeV. To some extent, such a reaction is similar to the process of “reverse fission”. Indeed, if the fission of a uranium nucleus into two fragments occurs with the release of energy (it is used in nuclear power plants), then in the reverse reaction, when the fragments merge, the resulting uranium nucleus will be almost cold. Therefore, when elements are synthesized in cold fusion reactions, a heavy nucleus only needs to emit one or two neutrons to go to the ground state.
Cold fusion reactions of massive nuclei were successfully used to synthesize 6 new elements, from 107 to 112 (P. Armbruster, Z. Hofmann, G. Münzenberg, etc.) at the GSI National Nuclear Physics Center in Darmstadt (Germany). Recently, K. Morita et al. at the RIKEN National Center (Tokyo) repeated the GSI experiments on the synthesis of 110-112 elements. Both groups intend to move on to elements 113 and 114 using heavier projectiles. However, attempts to synthesize increasingly heavier elements in cold fusion reactions are associated with great difficulties. With an increase in the atomic charge of ions, the probability of their fusion with target nuclei 208 Pb or 209 Bi decreases greatly due to an increase in Coulomb repulsive forces, which, as is known, are proportional to the product of the nuclear charges. From element 104, which can be obtained in the reaction 208 Pb + 50 Ti (Z 1 × Z 2 = 1804) to element 112 in the reaction 208 Pb + 70 Zn (Z 1 × Z 2 = 2460), the probability of merger decreases by more than 10 4 times.

Figure 3 Map of heavy nuclides. Nuclear half-lives are represented by different colors (right scale). Black squares are isotopes of stable elements found in the earth's crust (T 1/2 ≥ 10 9 years). Dark blue color is the “sea of ​​instability”, where nuclei live for less than 10 -6 seconds. Yellow lines correspond to closed shells indicating the magic numbers of protons and neutrons. “Islands of stability” following the “peninsula” of thorium, uranium and transuranium elements are predictions of the microscopic theory of the nucleus. Two nuclei with Z = 112 and 116, obtained in different nuclear reactions and their sequential decay, show how close one can get to the “islands of stability” during the artificial synthesis of superheavy elements.

There is another limitation. Compound nuclei obtained in cold fusion reactions have a relatively small number of neutrons. In the case of the formation of the 112th element considered above, the final nucleus with Z = 112 has only 165 neutrons, while an increase in stability is expected for the number of neutrons N > 170 (see Fig. 3).

Nuclei with a large excess of neutrons can, in principle, be obtained if artificial elements are used as targets: plutonium (Z=94), americium (Z=95) or curium (Z=96) produced in nuclear reactors, and rare elements as a projectile calcium isotope - 48 Ca. (see below).

The nucleus of the 48 Ca atom contains 20 protons and 28 neutrons - both values ​​​​correspond to closed shells. In fusion reactions with 48 Ca nuclei, their “magic” structure will also work (this role in cold fusion reactions was played by the magic nuclei of the target - 208 Pb), as a result of which the excitation energy of superheavy nuclei will be about 30 - 35 MeV. Their transition to the ground state will be accompanied by the emission of three neutrons and gamma rays. One could expect that at this excitation energy the effect of nuclear shells is still present in heated superheavy nuclei, this will increase their survival and allow us to synthesize them in our experiments. Note also that the asymmetry of the masses of interacting nuclei (Z 1 × Z 2 ≤ 2000) reduces their Coulomb repulsion and thereby increases the probability of merger.

Despite these seemingly obvious advantages, all previous attempts to synthesize superheavy elements in reactions with 48 Ca ions, undertaken in various laboratories in 1977 - 1985, failed. turned out to be ineffective. However, the development of experimental technology in recent years and, above all, the production in our laboratory of intense beams of 48 Ca ions on new generation accelerators, has made it possible to increase the sensitivity of the experiment by almost 1000 times. These achievements were used in a new attempt to synthesize superheavy elements.

3 Expected properties

What do we expect to see in the experiment if the synthesis is successful? If the theoretical hypothesis is true, then superheavy nuclei will be stable relative to spontaneous fission. Then they will experience another type of decay: alpha decay (emission of a helium nucleus consisting of 2 protons and 2 neutrons). As a result of this process, a daughter nucleus is formed that is 2 protons and 2 neutrons lighter than the parent nucleus. If the daughter nucleus has a low probability of spontaneous fission, then after the second alpha decay the grandchild nucleus will now be 4 protons and 4 neutrons lighter than the initial nucleus. Alpha decays will continue until spontaneous fission occurs (Fig. 4).

That. we expect to see not just one decay, but a “radioactive family”, a chain of successive alpha decays, quite long in time (on a nuclear scale), which compete with, but are ultimately interrupted by, spontaneous fission. In principle, such a decay scenario already indicates the formation of a superheavy nucleus.

To fully see the expected increase in stability, it is necessary to come as close as possible to the closed shells Z = 114 and N = 184. It is extremely difficult to synthesize such neutron-excess nuclei in nuclear reactions, since when merging nuclei of stable elements that already have a certain ratio of protons and neutrons, it is impossible to get to the doubly magic nucleus 298 114. Therefore, we need to try to use nuclei in the reaction that initially contain the maximum possible number of neutrons. This, to a large extent, also determined the choice of accelerated 48 Ca ions as a projectile. As you know, there is a lot of calcium in nature. It consists of 97% of the isotope 40 Ca, the nucleus of which contains 20 protons and 20 neutrons. But it contains 0.187% heavy isotope - 48 Ca (20 protons and 28 neutrons) which has 8 excess neutrons. The technology for its production is very labor-intensive and expensive; the cost of one gram of enriched 48 Ca is about $200,000. Therefore, we had to significantly change the design and operating modes of our accelerator in order to find a compromise solution - to obtain the maximum intensity of the ion beam with a minimum consumption of this exotic material.

Figure 4
Theoretical predictions about the decay types (shown in different colors in the figure) and half-lives of isotopes of superheavy elements with different numbers of protons and neutrons. As an example, it is shown that for the isotope of the 116th element with a mass of 293, formed in the fusion reaction of nuclei 248 St and 48 Ca, three successive alpha decays are expected, which end with the spontaneous fission of the great-grandson nucleus of the 110th element with a mass of 281. As can be seen in Fig. 8 is exactly such a decay scenario, in the form of a chain α - α - α - SF, observed for this nucleus in experiment. The decay of a lighter nucleus is the isotope of the 110th element with a mass of 271 obtained in the “cold fusion” reaction of nuclei 208 Pb + 64 Ni. Its half-life is 10 4 times less than that of the isotope 281 110.

Today we reached a record beam intensity - 8 × 10 12 / s, with a very low consumption of the 48 Ca isotope - about 0.5 milligrams / hour. As target material we use long-lived enriched isotopes of artificial elements: Pu, Am, Cm and Cf (Z = 94-96 and 98) also with a maximum neutron content. They are produced in powerful nuclear reactors (in Oak Ridge, USA and in Dimitrovgrad, Russia) and then enriched in special installations, mass separators at the All-Russian Research Institute of Experimental Physics (Sarov). Fusion reactions of 48 Ca nuclei with nuclei of these isotopes were chosen for the synthesis of elements with Z = 114 - 118.

Here I would like to make some digression.

Not every laboratory, even the leading nuclear centers in the world, has such unique materials and in such quantities that we use in our work. But the technologies for their production have been developed in our country and they are being developed by our industry. The Minister of Atomic Energy of Russia suggested that we develop a program of work on the synthesis of new elements for 5 years and allocated a special grant for carrying out this research. On the other hand, working at the Joint Institute for Nuclear Research, we widely collaborate (and compete) with leading laboratories in the world. In research on the synthesis of superheavy elements, we have been closely collaborating for many years with the Livermore National Laboratory (USA). This collaboration not only combines our efforts, but also creates conditions under which experimental results are processed and analyzed independently by two groups at all stages of the experiment.
Over 5 years of work, during long-term irradiation, a dose of about 2 × 10 20 ions (about 16 milligrams of 48 Ca, accelerated to ~ 1/10 the speed of light, passed through the target layers). In these experiments, the formation of isotopes of 112÷118 elements (with the exception of the 117th element) was observed and the first results were obtained on the decay properties of new superheavy nuclides. Presenting all the results would take too much space and, in order not to bore the reader, we will limit ourselves to describing only the last experiment on the synthesis of 113 and 115 elements - all other reactions were studied in a similar way. But before embarking on this task, it would be advisable to briefly outline the setup of the experiment and explain the basic principles of operation of our installation.

4. Setting up the experiment

Figure 5
Schematic view of the installation for the separation of recoil nuclei in experiments on the synthesis of heavy elements

Mentally, the entire surface of the detector can be represented as about 500 cells (pixels) in which decays are detected. The probability that two signals will randomly fall into the same place is 1/500, three signals - 1/250000, etc. This makes it possible to select, with great reliability, from a huge number of radioactive products very rare events of genetically related sequential decays of superheavy nuclei, even if they are formed in extremely small quantities (~1 atom/month).

5. Experimental results

In order to show the installation “in action”, we will describe, as an example, in more detail the experiments on the synthesis of element 115 formed in the fusion reaction of nuclei 243 Am(Z=95) + 48 Ca(Z=20) → 291 115.
The synthesis of a Z-odd nucleus is attractive because the presence of an odd proton or neutron significantly reduces the probability of spontaneous fission and the number of successive alpha transitions will be greater (long chains) than in the case of the decay of even-even nuclei. To overcome the Coulomb barrier, 48 Ca ions must have an energy E > 236 MeV. On the other hand, fulfilling this condition, if we limit the beam energy to E = 248 MeV, then the thermal energy of the compound nucleus 291 115 will be about 39 MeV; its cooling will occur through the emission of 3 neutrons and gamma rays. Then the reaction product will be the isotope 115 of the element with the number of neutrons N=173. Having flown out of the target layer, an atom of a new element will pass through a separator configured to transmit it and enter the detector. Further events develop as shown in Fig. 6. 80 microseconds after the recoil core stops in the frontal detector, the data acquisition system receives signals about its arrival time, energy and coordinates (strip number and position in it). Note that this information has the "TOF" (came from the separator) attribute. If within 10 seconds a second signal with an energy of more than 9.8 MeV follows from the same place on the detector surface, without the “TOF” sign (i.e. from the decay of the implanted atom), the beam is turned off and all further decay is recorded in conditions of almost complete absence of background. As can be seen in the top graph of Fig. 6, behind the first two signals - from the recoil nucleus and the first alpha particle - for a time of about 20 s. after the beam was turned off, 4 other signals followed, the positions of which, with an accuracy of ± 0.5 mm, coincided with the previous signals. Over the next 2.5 hours the detector was silent. Spontaneous fission in the same strip and in the same position was recorded only the next day, 28.7 hours later, in the form of two signals from fission fragments with a total energy of 206 MeV.
Such chains were registered three times. They all have the same appearance (6 generations of nuclei in the radioactive family) and are consistent with each other both in the energy of alpha particles and in the time of their appearance, taking into account the exponential law of nuclear decay. If the observed effect relates, as expected, to the decay of the isotope of element 115 with a mass of 288, formed after the evaporation of 3 neutrons by a compound nucleus, then with an increase in the energy of the 48 Ca ion beam by only 5 MeV, it should decrease by 5-6 times. Indeed, at E = 253 MeV there was no effect. But here another, shorter, chain of decays was observed, consisting of four alpha particles (we believe that there were also 5 of them, but the last alpha particle flew out of the open window) lasting only 0.4 s. The new chain of decays ended after 1.5 hours with spontaneous fission. Obviously, this is the decay of another nucleus, most likely the neighboring isotope of the 115th element with a mass of 287, formed in a fusion reaction with the emission of 4 neutrons. The chain of successive decays of the odd-odd isotope Z=115, N=173 is presented in the lower graph of Fig. 6, which shows the calculated half-lives of superheavy nuclides with different numbers of protons and neutrons in the form of a contour map. It also shows the decay of another, lighter odd-odd isotope of the 111th element with the number of neutrons N = 161 synthesized in the reaction 209 Bi+ 64 Ni in the German Laboratory - GSI (Darmstadt) and then in the Japanese - RIKEN (Tokyo).

Figure 6
Experiment on the synthesis of element 115 in the reaction 48 Ca + 243 At.
The top figure shows the times at which signals appear after implantation of a recoil nucleus (R) into the detector. Signals from the registration of alpha particles are marked in red, signals from spontaneous fission are marked in green. As an example, for one of the three events the positional coordinates (in mm) of all 7 signals from the R → decay chain are givenα 1 → α 2 → α 3 → α 4 →α 5 → SF recorded in strip No. 4. The lower figure shows the decay chains of nuclei with Z=111, N=161 and Z=115, N=173. Contour lines outlining regions of nuclei with different half-lives (different degrees of darkening) are predictions of microscopic theory.

First of all, it should be noted that the nuclear half-lives in both cases are in good agreement with theoretical predictions. Despite the fact that the isotope 288 115 is removed from the neutron shell N=184 by 11 neutrons, the isotopes 115 and 113 elements have a relatively long lifetime (T 1/2 ~ 0.1 s and 0.5 s, respectively).
After five alpha decays, isotope 105 of the element is formed - dubnium (Db) with N=163, the stability of which is determined by another closed shell N=162. The power of this shell is demonstrated by the huge difference in the half-lives of two Db isotopes differing from each other by only 8 neutrons. Let us note, once again, that in the absence of structure (nuclear shells), all isotopes of 105÷115 elements would have to undergo spontaneous fission in a time of ~ 10 -19 s.

(chemical experiment)

In the example described above, the properties of the long-lived isotope 268 Db, which completes the decay chain of element 115, are of independent interest.
According to the Periodic Law, element 105 is in row V. It is, as can be seen in Fig. 7, a chemical homologue of niobium (Nb) and tantalum (Ta) and differs in chemical properties from all lighter elements - actinides (Z = 90÷103) representing a separate group in the D.I. Table. Mendeleev. Due to its long half-life, this isotope of element 105 can be separated from all reaction products radiochemical method followed by measurement of its decay - spontaneous fission. This experiment provides an independent identification of the atomic number of the final nucleus (Z = 105) and of all nuclides produced in the successive alpha decays of element 115.
In a chemical experiment there is no need to use a recoil nuclei separator. The separation of reaction products by their atomic numbers is carried out by methods based on the difference in their chemical properties. Therefore, a more simplified technique was used here. The reaction products flying out of the target were driven into a copper collector located along the path of their movement to a depth of 3-4 microns. After 20-30 hours of irradiation, the collection dissolved. A fraction of transactinoids - elements Z > 104 - was isolated from the solution, and from this fraction, then the elements of the 5th series - Db, accompanied by their chemical homologues Nb and Ta. The latter were added as “markers” to the solution before chemical separation. A droplet of a solution containing Db was deposited on a thin substrate, dried, and then placed between two semiconductor detectors that recorded both fragments of spontaneous fission. The entire assembly was, in turn, placed in a neutron detector, which determined the number of neutrons emitted by fragments during the fission of Db nuclei.
In June 2004, 12 identical experiments were carried out (S.N. Dmitriev and others), in which 15 events of spontaneous division of Db were recorded. Spontaneous fission fragments Db have a kinetic energy of about 235 MeV, and an average of about 4 neutrons are emitted for each fission event. Such characteristics are inherent in the spontaneous fission of a fairly heavy nucleus. Let us recall that for 238 U these values ​​are approximately 170 MeV and 2 neutrons, respectively.
Chemical experiment confirms the results of physical experiment: the nuclei of the 115th element formed in the reaction 243 Am + 48 Ca as a result of successive five alpha decays: Z = 115 → 113 → 111 → 109 → 107 → 105 actually lead to the formation of a long-lived spontaneously fissile nucleus with atomic number 105. In these experiments, as a daughter product of the alpha decay of element 115, another, previously unknown element with atomic number 113 was also synthesized.

Figure 7
Physical and chemical experiments to study the radioactive properties of the 115th element.
In the reaction 48 Ca + 243 At, using a physical setup it was shown that five consecutive
alpha decays of the isotope 288 115 lead to the long-lived isotope of the 105th element - 268 Db, which
splits spontaneously into two fragments. In a chemical experiment, it was determined that a nucleus with atomic number 105 undergoes spontaneous fission.

6. The big picture and the future

Prospects

Now the task is to study in more detail the nuclear and atomic structure of new elements, which is very problematic, primarily due to the low yield of the desired reaction products. In order to increase the number of atoms of superheavy elements, it is necessary to increase the intensity of the 48 Ca ion beam and increase the efficiency of physical techniques. The modernization of the heavy ion accelerator, planned for the coming years, using all the latest achievements in accelerator technology, will allow us to increase the intensity of the ion beam by approximately 5 times. The solution to the second part requires a radical change in the experimental setup; it can be found in the creation of a new experimental technique based on the properties of superheavy elements.

Figure 8
Map of nuclides of heavy and superheavy elements.
For the nuclei inside the ovals corresponding to the various fusion reactions (shown in the figure), the half-lives and energies of the emitted alpha particles are given (yellow squares). The data is presented on a contour map of the separating region based on the contribution of the nuclear shell effect to the nuclear binding energy. In the absence of nuclear structure, the entire field would be white. As they darken, the effect of the shells increases. Two neighboring zones differ by only 1 MeV. This, however, is sufficient to significantly increase the stability of nuclei relative to spontaneous fission, as a result of which nuclides located near the “magic” numbers of protons and neutrons experience predominantly alpha decay. On the other hand, in the isotopes of the 110th and 112th elements, an increase in the number of neutrons by 8 atomic units leads to an increase in the periods of alpha decay of nuclei by more than 10 5 times.

The operating principle of the current installation - the kinematic separator of recoil nuclei (Fig. 5) is based on the difference in the kinematic characteristics of different types of reactions. The products of the reaction of fusion of target nuclei and 48 Ca that interest us fly out of the target in the forward direction, in a narrow angular cone ± 3 0 with a kinetic energy of about 40 MeV. By limiting the trajectories of recoil nuclei, taking these parameters into account, we almost completely tune out the ion beam, suppress the background of reaction by-products by a factor of 10 4 ÷ 10 6, and deliver atoms of new elements to the detector with an efficiency of approximately 40% in 1 microsecond. In other words, separation of reaction products occurs “on the fly”.

Figure 8 MASHA installation
The top figure shows a diagram of the separator and the principle of its operation. Recoil nuclei ejected from the target layer are stopped in a graphite collector at a depth of several micrometers. Due to the high temperature of the collector, they diffuse into the ion source chamber, are drawn out of the plasma, accelerated by the electric field, and are analyzed by mass by magnetic fields as they move towards the detector. In this design, the mass of an atom can be determined with an accuracy of 1/3000. The figure below shows a general view of the installation.

But in order to obtain high selectivity of the installation, it is important to preserve and not “smear” the kinematic parameters - departure angles and energies of recoil nuclei. Because of this, it is necessary to use target layers with a thickness of no more than 0.3 micrometers - approximately three times less than what is needed to obtain an effective yield of a superheavy nucleus with a given mass or 5–6 times less if we are talking about the synthesis of two isotopes of a given element neighboring in mass. In addition, in order to obtain data on the mass numbers of isotopes of a superheavy element, it is necessary to carry out a long and labor-intensive series of experiments - repeating measurements at different energies of the 48 Ca ion beam.
At the same time, as follows from our experiments, the synthesized atoms of superheavy elements have half-lives that significantly exceed the speed of the kinematic separator. Therefore, in many cases, there is no need to separate reaction products in such a short time. Then you can change the operating principle of the installation and separate the reaction products in several stages.
The diagram of the new installation is shown in Fig. 9. After implantation of recoil nuclei into a collector heated to a temperature of 2000 0 C, the atoms diffuse into the plasma of the ion source, are ionized in the plasma to a charge q = 1 +, are drawn out of the source by an electric field, are separated by mass in magnetic fields of a special profile and, finally, are registered (by decay type) by detectors located in the focal plane. The entire procedure can take, according to estimates, time from tenths of a second to several seconds, depending on the temperature conditions and physicochemical properties of the separated atoms. Inferior in speed to the kinematic separator, the new installation is MASHA (an abbreviation for the full name Mass Analyzer of Super Heavy Atoms) - will increase the operating efficiency by about 10 times and provide, along with the decay properties, a direct measurement of the mass of superheavy nuclei.
Thanks to a grant allocated by the Governor of the Moscow Region B.V. Gromov to create this installation, it was designed and manufactured in a short time - in 2 years, passed tests and is ready for operation. After reconstruction of the accelerator, with the installation of MASHA. We will significantly expand our research into the properties of new nuclides and try to go further into the region of heavier elements.

(search for superheavy elements in nature)

Another side of the problem of superheavy elements is related to the production of longer-lived nuclides. In the experiments described above, we only approached the edge of the “island”, discovered a steep rise, but are still far from its top, where nuclei can live for thousands and, perhaps, even millions of years. We do not have enough neutrons in the synthesized nuclei to get closer to the N=184 shell. Today this is unattainable - there are no reactions that would make it possible to obtain such neutron-rich nuclides. Perhaps in the distant future, physicists will be able to use intense beams of radioactive ions, with a number of neutrons greater than those of 48 Ca nuclei. Such projects are now being widely discussed, without yet touching on the costs required to create such accelerating giants.

However, you can try to approach this problem from a different angle.

If we assume that the longest-lived superheavy nuclei have a half-life of 10 5 ÷ 10 6 years (not much at odds with the predictions of the theory, which also makes its estimates with a certain accuracy), then it is possible that they can be detected in cosmic rays - witnesses of the formation elements on other, younger planets of the Universe. If we make an even stronger assumption that the half-lives of the "long-lived" could be tens of millions of years or more, then they could be present in the Earth, surviving in very small quantities from the formation of the elements in the solar system to the present day.
Among possible candidates, we give preference to isotopes of element 108 (Hs), whose nuclei contain about 180 neutrons. Chemical experiments carried out with the short-lived isotope 269 Hs (T 1/2 ~ 9 s) showed that element 108, as expected, according to the Periodic Law, is a chemical homologue of the 76th element - osmium (Os).

Figure 10
Installation for recording a burst of neutrons from spontaneous fission of nuclei during the decay of element 108. (Underground laboratory in Modan, France)

Then a sample of metallic osmium may contain the 108 element Eka(Os) in very small quantities. The presence of Eka(Os) in osmium can be determined by its radioactive decay. Perhaps the superheavy long-liver will experience spontaneous fission, or spontaneous fission will occur after previous alpha or beta decays (a type of radioactive transformation in which one of the neutrons of the nucleus turns into a proton) of a lighter and shorter-lived daughter or grandchild nucleus. Therefore, at the first stage, it is possible to carry out an experiment to register rare events of spontaneous fission of an osmium sample. Such an experiment is being prepared. Measurements will begin at the end of this year and will continue for 1-1.5 years. The decay of a superheavy nucleus will be detected by the neutron burst accompanying the spontaneous fission. In order to protect the installation from the neutron background generated by cosmic rays, measurements will be carried out in an underground laboratory located under the Alps in the middle of a tunnel connecting France with Italy at a depth corresponding to a 4000-meter layer of water equivalent.
If during a year of measurements at least one event of spontaneous fission of a superheavy nucleus is observed, then this will correspond to a concentration of element 108 in the Os sample of about 5 × 10 -15 g/g, assuming that its half-life is 10 9 years. Such a small value is only 10 -16 part of the concentration of uranium in the earth's crust.
Despite the ultra-high sensitivity of the experiment, the chances of detecting relict, superheavy nuclides are small. But any scientific search always has a small chance... The absence of an effect will give an upper limit on the half-life of a centenarian at the level of T 1/2 ≤ 3× 10 7 years. Not so impressive, but important for understanding the properties of nuclei in the new region of stability of superheavy elements.

Search results for \"stable elements\". About superheavy elements Superheavy elements on the stability island Theoretical and experimental study of the stability of the nucleus gave Soviet physicists a reason to revise the previously used methods for producing heavy transuraniums. In Dubna they decided to take new paths and target lead And bismuth. The nucleus, like the atom as a whole, has shell structure. Particularly stable are atomic nuclei containing 2-8-20-28-50-82-114-126-164 protons (that is, atomic nuclei with the same atomic number) and 2-8-20-28-50-82-126- 184-196-228-272-318 neutrons, due to the complete structure of their shells. Only recently was it possible to confirm these views by computer calculations. This unusual stability caught my eye, first of all, when studying the prevalence of certain elements in space. Isotopes, possessing these nuclear numbers are called magic. The bismuth isotope 209Bi, which has 126 neutrons, is such a magic nuclide. This also includes isotopes oxygen, calcium, tin. Twice magic are: for helium - the isotope 4 He (2 protons, 2 neutrons), for calcium - 48 Ca (20 protons, 28 neutrons), for lead - 208 Pb (82 protons, 126 neutrons). They are distinguished by a very special core strength. Using ion sources of a new type and more powerful heavy ion accelerators - U-200 and U-300 units were paired in Dubna, the group of G. N. Flerov and Yu. Ts. Oganesyan soon began to have flow of heavy ions with extraordinary energy. To achieve nuclear fusion, Soviet physicists fired chromium ions with an energy of 280 MeV at targets made of lead and bismuth. What could have happened? At the beginning of 1974, nuclear scientists in Dubna recorded 50 cases of such bombing, indicating formation of element 106, which, however, decays after 10 -2 s. These 50 atomic nuclei were formed according to the scheme: 208 Pb + 51 Cr = 259 X A little later, Ghiorso and Seaborg of the Lawrence Berkeley Laboratory reported that they had synthesized an isotope of a new 106 -th, element with mass number 263 by bombarding californium-249 with oxygen ions in the Super-HILAC apparatus. What name will the new element have? Putting aside previous differences, both groups in Berkeley and Dubna, competing in a scientific competition, this time came to a consensus. It’s too early to talk about names, Oganesyan said. And Ghiorso added that it was decided to refrain from any proposals about the name of the 106th element until the situation is clarified. By the end of 1976, the Dubna nuclear reaction laboratory completed a series of experiments on the synthesis of element 107; served as a starting substance for the Dubna “alchemists” magical"bismuth-209. When bombarded with chromium ions with an energy of 290 MeV, it turned into an isotope 107 -th element: 209 Bi + 54 Cr = 261 X + 2 n Element 107 decays spontaneously with a half-life of 0.002 s and also emits alpha particles. The half-lives of 0.01 and 0.002 s found for the 106th and 107th elements made us wary. After all, they turned out to be several orders of magnitude larger than predicted by computer calculations. Perhaps the 107th element was already noticeably influenced by the proximity of the subsequent magic number of protons and neutrons - 114, increasing stability? If this is so, then there was hope to obtain long-lived isotopes of element 107, for example, by shelling Berkeley neon ions. Calculations showed that the neutron-rich isotope formed by this reaction would have a half-life exceeding 1 s. This would make it possible to study the chemical properties of element 107 - ecarenia. The longest-lived isotope of the first transuranium, element 93, neptunium-237, has a half-life of 2,100,000 years; the most stable isotope of element 100, fermium-257, lasts only 97 days. Starting from element 104 half-lives are only fractions of a second. Therefore, there seemed to be absolutely no hope of discovering these elements. Why is further research needed? Albert Ghiorso, a leading US specialist on transuraniums, once spoke in this regard: " The reason for continuing to search for further elements is simply to satisfy human curiosity - what is happening around the next corner of the street?“However, this, of course, is not just scientific curiosity. Ghiorso still made it clear how important it is to continue such fundamental research. In the 60s, the theory of magic nuclear numbers became increasingly important. In the "sea of ​​instability" scientists desperately tried to find a life-saving " island of relative stability", on which the foot of an atomic explorer could firmly rest. Although this island has not yet been discovered, its "coordinates" are known: element 114, ekas lead, is considered the center of a large stability region. Isotope 298 of element 114 has long been a particular subject of scientific debate because, with 114 protons and 184 neutrons, it is one of those doubly magical atomic nuclei predicted to last for a long time. However, what does long-term existence mean? Preliminary calculations show: the half-life with the release of alpha particles ranges from 1 to 1000 years, and in relation to spontaneous fission - from 10 8 to 10 16 years. Such fluctuations, as physicists point out, are explained by the approximation of “computer chemistry.” Very encouraging half-lives are predicted for the next island of stability - element 164, dvislead. The isotope of element 164 with mass number 482 is also doubly magical: its nucleus is formed by 164 protons and 318 neutrons. Science is interesting and simple magical superheavy elements, such as isotope-294 of element 110 or isotope-310 of element 126, containing 184 neutrons. It’s amazing how researchers quite seriously juggle these imaginary elements, as if they already exist. More and more new data is being extracted from the computer and it is now definitely known what properties - nuclear, crystallographic and chemical - these superheavy elements must have. The specialized literature is accumulating precise data for elements that people will perhaps discover in 50 years. Atomic scientists are currently navigating the sea of ​​instability, awaiting discoveries. Behind them was solid ground: a peninsula with natural radioactive elements, marked by hills of thorium and uranium, and a far-reaching solid ground with all the other elements and peaks lead, tin And calcium. Brave sailors have been on the high seas for a long time. In an unexpected place, they found a sandbank: open elements 106 and 107 were more stable than expected. In recent years, we have been sailing for a long time on a sea of ​​instability, argues G. N. Flerov, and suddenly, at the last moment, we felt the ground under our feet. Random underwater rock? Or a sandbank of a long-awaited island of stability? If the second is correct, then we have a real opportunity to create a new periodic system of stable superheavy elements with amazing properties. After the hypothesis about stable elements near serial numbers 114, 126, 164 became known, researchers around the world pounced on these " super heavy"atoms. Some of them, with presumably long half-lives, were hoped to be found on Earth or in Space, at least in the form of traces. After all, when our Solar system arose, these elements existed just like all the others. Traces of superheavy elements- what should be understood by this? As a result of their ability to spontaneously fission into two nuclear fragments with great mass and energy, these transurans would have to leave distinct traces of destruction in the surrounding matter. Similar traces can be seen in minerals under a microscope after they have been etched. Using this method of destruction traces, it is now possible to trace the existence of long-dead elements. From the width of the traces left, one can also estimate the ordinal number of the element - the width of the track is proportional to the square of the nuclear charge. They also hope to identify “living” superheavy elements based on the fact that they repeatedly emit neutrons. During the spontaneous fission process, these elements emit up to 10 neutrons. Traces of superheavy elements were searched for in manganese nodules from the depths of the ocean, as well as in waters after the melting of glaciers in the polar seas. Still no results. G. N. Flerov and his colleagues examined the lead glass of an ancient showcase from the 14th century, a Leyden jar from the 19th century, and a lead crystal vase from the 18th century. At first, several traces of spontaneous fission indicated ekas lead- 114th element. However, when the Dubna scientists repeated their measurements with a highly sensitive neutron detector in the deepest salt mine of the Soviet Union, they did not get a positive result. Cosmic radiation, which apparently caused the observed effect, could not penetrate to such a depth. In 1977, Professor Flerov suggested that he had finally discovered " signals of new transuranium" while studying the deep thermal waters of the Cheleken Peninsula in the Caspian Sea. However, the number of reported cases was too small for a clear assignment. A year later, Flerov’s group registered 150 spontaneous divisions per month. These data were obtained while working with an ion exchanger filled with unknown transuranium from thermal waters. Flerov estimated the half-life of the element present, which he had not yet been able to isolate, to be billions of years. Other researchers took different paths. Professor Fowler and his colleagues from the University of Bristol undertook experiments with balloons at high altitude. Using detectors of small quantities of nuclei, numerous areas with nuclear charges exceeding 92 were identified. English researchers believed that one of the traces even pointed to elements 102...108. Later they made an amendment: the unknown element has serial number 96 ( curium). How do these superheavy particles get into the stratosphere of the globe? Several theories have been put forward so far. According to them, heavy atoms should appear during supernova explosions or other astrophysical processes and reach the Earth in the form of cosmic radiation or dust - but only after 1000 - 1,000,000 years. These cosmic deposits are currently being sought both in the atmosphere and in deep marine sediments. So, superheavy elements can be found in cosmic radiation? True, according to the American scientists who undertook the Skylab experiment in 1975, this hypothesis was not confirmed. In a space laboratory that orbited the Earth, detectors were installed that absorb heavy particles from space; were only discovered tracks of known elements. Lunar dust brought to Earth after the first lunar landing in 1969 was no less carefully examined for the presence of superheavy elements. When traces of “long-lived” particles up to 0.025 mm were found, some researchers believed that they could be attributed to elements 110 - 119. Similar results were obtained from studies of the anomalous isotopic composition of the noble gas xenon contained in various meteorite samples. Physicists have expressed the opinion that this effect can only be explained by the existence of superheavy elements. Soviet scientists in Dubna, who analyzed 20 kg of the Allende meteorite, which fell in Mexico in the fall of 1969, were able to detect several spontaneous fissions as a result of three months of observation. However, after it was established that "natural" plutonium-244, which was once an integral part of our solar system, leaves completely similar traces, the interpretation began to be carried out more carefully. A century and a half ago, when Dmitry Ivanovich Mendeleev discovered the Periodic Law, only 63 elements were known. Arranged in a table, they were easily laid out into periods, each of which opens with active alkali metals and ends (as it turned out later) with inert noble gases. Since then, the periodic table has almost doubled in size, and with each expansion the Periodic Law has been confirmed again and again. Rubidium is also reminiscent of potassium and sodium, as xenon is of krypton and argon; below carbon is silicon, which is much similar to it... Today it is known that these properties are determined by the number of electrons rotating around the atomic nucleus. They fill the “energy shells” of the atom one after another, like spectators occupying their seats in order in a theater: the one who is last will determine the chemical properties of the entire element. An atom with a completely filled last shell (like helium with its two electrons) will be inert; an element with one “extra” electron on it (like sodium) will actively form chemical bonds. The number of negatively charged electrons in orbits is related to the number of positive protons in the nucleus of an atom, and it is the number of protons that distinguishes different elements. But there can be different numbers of neutrons in the nucleus of the same element; they have no charge, and they do not affect the chemical properties. But depending on the number of neutrons, hydrogen may turn out to be heavier than helium, and the mass of lithium may reach seven instead of the “classical” six atomic units. And if the list of known elements today is approaching 120, then the number of nuclei (nuclides) has exceeded 3000. Most of them are unstable and after some time decay, releasing “extra” particles during radioactive decay. Even more nuclides are unable to exist in principle, instantly falling apart into pieces. Thus, a continent of stable nuclei is surrounded by a whole sea of ​​unstable combinations of neutrons and protons. Sea of ​​Instability The fate of the nucleus depends on the number of neutrons and protons in it. According to the shell theory of the structure of the nucleus, put forward back in the 1950s, the particles in it are distributed among their energy levels in the same way as electrons that rotate around the nucleus. Some numbers of protons and neutrons give particularly stable configurations with completely filled proton or neutron shells - 2, 8, 20, 28, 50, 82, and for neutrons there are also 126 particles. These numbers are called “magic” numbers, and the most stable nuclei contain “twice-magic” numbers of particles—for example, lead has 82 protons and 126 neutrons, or two each in a normal atom of helium, the second most abundant element in the universe. The successive "Chemical Continent" of elements found on Earth ends with lead. It is followed by a series of nuclei that exist much less than the age of our planet. In its depths they can only be preserved in small quantities, like uranium and thorium, or even in trace amounts, like plutonium. It is impossible to extract it from the rock, and plutonium is produced artificially, in reactors, bombarding a uranium target with neutrons. In general, modern physicists treat atomic nuclei as construction parts, forcing them to attach individual neutrons, protons or entire nuclei. This makes it possible to obtain increasingly heavier nuclides by crossing the strait of the “Sea of ​​Instability”. The purpose of the journey is suggested by the same shell theory of the structure of the nucleus. This is the region of superheavy elements with a suitable (and very large) number of neutrons and protons, the legendary “Island of Stability”. Calculations say that some of the local “residents” may no longer exist for fractions of microseconds, but for many orders of magnitude longer. “To a certain approximation, they can be considered as droplets of water,” RAS Academician Yuri Oganesyan explained to us. — Up to lead, the nuclei are spherical and stable. Following them is a peninsula of moderately stable nuclei - such as thorium or uranium - which is stretched out by a shoal of highly deformed nuclei and breaks into an unstable sea... But even further, beyond the strait, there may be a new region of spherical nuclei, superheavy and stable elements with numbers 114, 116 and further." The lifetime of some elements on the “Island of Stability” can last for years, or even millions of years. Island of Stability Transuranic elements with their deformed nuclei can be created by bombarding targets made of uranium, thorium or plutonium with neutrons. By bombarding them with light ions accelerated in an accelerator, you can successively obtain a number of even heavier elements - but at some point the limit will come. “If we consider different reactions—the addition of neutrons, the addition of ions—as different “ships,” then all of them will not help us sail to the “Island of Stability,” continues Yuri Oganesyan. — This will require a larger “vessel” and a different design. The target would have to be neutron-rich heavy nuclei of artificial elements heavier than uranium, and they would have to be bombarded with large, heavy isotopes containing many neutrons, such as calcium-48.” Only a large international team of scientists could work on such a “ship”. Engineers and physicists at the Elektrokhimpribor plant isolated from natural calcium the extremely rare 48th isotope, which is contained here in an amount of less than 0.2%. Targets from uranium, plutonium, americium, curium, californium were prepared at the Dimitrograd Research Institute of Atomic Reactors, at the Livermore National Laboratory and at the Oak Ridge National Laboratory in the USA. Well, key experiments on the synthesis of new elements were carried out by Academician Oganesyan at the Joint Institute of Nuclear Physics (JINR), at the Flerov Laboratory of Nuclear Reactions. “Our accelerator in Dubna worked 6-7 thousand hours a year, accelerating calcium-48 ions to approximately 0.1 the speed of light,” explains the scientist. “This energy is necessary so that some of them, hitting the target, overcome the forces of Coulomb repulsion and merge with the nuclei of its atoms. For example, element 92, uranium, will produce the nucleus of a new element numbered 112, plutonium 114, and californium 118.” “The search for new superheavy elements allows us to answer one of the most important questions of science: where lies the border of our material world?” “Such nuclei should already be quite stable and will not decay immediately, but will gradually emit alpha particles and helium nuclei. And we are very good at registering them,” continues Oganesyan. The superheavy nucleus will eject an alpha particle, transforming into an element two atomic numbers lighter. In turn, the daughter nucleus will lose an alpha particle and turn into a “grandchild” - four more lighter, and so on, until the process of sequential alpha decay ends with the random appearance and instantaneous spontaneous fission, the death of the unstable nucleus in the “Sea of ​​Instability”. Using this “genealogy” of alpha particles, Oganesyan and his colleagues traced the entire history of the transformation of nuclides obtained in the accelerator and outlined the near shore of the “Island of Stability.” After half a century of voyage, the first people landed on it. New land Already in the first decade of the 21st century, in the fusion reactions of actinides with accelerated calcium-48 ions, atoms of elements with numbers from 113 to 118, lying on the shore of the “Island of Stability” farthest from the “mainland”, were synthesized. Their lifetime is already orders of magnitude longer than that of their neighbors: for example, element 114 is stored not for milliseconds, like the 110th, but for tens and even hundreds of seconds. “Such substances are already available for chemistry,” says Academician Oganesyan. - This means that we are returning to the very beginning of the journey and now we can check whether Mendeleev’s Periodic Law is observed for them. Will element 112 be an analogue of mercury and cadmium, and element 114 an analogue of tin and lead? The first chemical experiments with the isotope of the 112th element (copernicium) showed that, apparently, they will. Copernicium nuclei ejected from the target during bombardment were directed by scientists into a long tube containing 36 paired detectors, partially coated with gold. Mercury easily forms stable intermetallic compounds with gold (this property is used in the ancient technique of gilding). Therefore, mercury and atoms close to it should settle on the gold surface of the very first detectors, and radon and atoms close to noble gases can reach the end of the tube. Obediently following the Periodic Law, Copernicium proved to be a relative of mercury. But if mercury was the first known liquid metal, then copernicium may be the first gaseous one: its boiling point is below room temperature. According to Yuri Oganesyan, this is only a faded beginning, and superheavy elements from the “Island of Stability” will open up a new, bright and unusual area of ​​chemistry for us. But for now we lingered at the foot of the island of stable elements. It is expected that the 120th and subsequent nuclei may turn out to be truly stable and will exist for many years, or even millions of years, forming stable compounds. However, it is no longer possible to obtain them using the same calcium-48: there are no sufficiently long-lived elements that could combine with these ions to give nuclei of the required mass. Attempts to replace calcium-48 ions with something heavier have also not yielded results. Therefore, for new searches, marine scientists raised their heads and took a closer look at the skies. Space and factory The original composition of our world was not very diverse: in the Big Bang, only hydrogen appeared with small admixtures of helium - the lightest of atoms. All other respected participants in the periodic table appeared in nuclear fusion reactions, in the interior of stars and during supernova explosions. Unstable nuclides quickly decayed, while stable nuclides, like oxygen-16 or iron-54, accumulated. It is not surprising that heavy unstable elements such as americium or copernicium cannot be found in nature. But if there really is an “Island of Stability” somewhere, then at least in small quantities superheavy elements should be found throughout the vastness of the Universe, and some scientists are searching for them among cosmic ray particles. According to Academician Oganesyan, this approach is still not as reliable as good old bombing. “The truly long-lived nuclei at the top of Stability Island contain unusually large amounts of neutrons,” says the scientist. “That’s why neutron-rich calcium-48 turned out to be such a successful nucleus for bombarding neutron-rich target elements.” However, isotopes heavier than calcium-48 are unstable, and the chances of them fusing to form super-stable nuclei under natural conditions are extremely low.” Therefore, the laboratory in Dubna near Moscow turned to the use of heavier nuclei, albeit not as successful as calcium, for firing at artificial target elements. “We are now busy creating the so-called Factory of Superheavy Elements,” says Academician Oganesyan. — In it, the same targets will be bombarded with titanium or chromium nuclei. They contain two and four more protons than calcium, which means they can give us elements with masses of 120 or more. It will be interesting to see whether they will still be on the “island” or whether they will open a new strait beyond it.”	At the energy of krypton ions near the Coulomb barrier, three cases of the formation of element 118 were observed. 293,118 nuclei were implanted into a silicon detector and a chain of six successive α-decays was observed, which ended in the isotope 269 Sg. The cross section for the formation of element 118 was ~2 picobarns. The half-life of isotope 293118 is 120 ms. In Fig. Figure 3 shows a chain of successive α-decays of the isotope 293 118 and shows the half-lives of daughter nuclei formed as a result of α-decays. Based on various theoretical models, the decay characteristics of superheavy nuclei were calculated. The results of one such calculation are shown in Fig. 4. The half-lives of even-even superheavy nuclei are given relative to spontaneous fission (a), α-decay (b), β-decay (c) and for all possible decay processes (d). The most stable nucleus with respect to spontaneous fission (Fig. 4a) is the nucleus with Z = 114 and N = 184. For it, the half-life with respect to spontaneous fission is ~10 16 years. For isotopes of element 114, which differ from the most stable one by 6-8 neutrons, half-lives decrease by 10-15 orders of magnitude. The half-lives relative to α-decay are shown in Fig. 4b. The most stable core is located in the Z region< 114 и N = 184 (T 1/2 = 10 15 лет). Для изотопа 298 114 период полураспада составляет около 10 лет. Nuclei stable with respect to β-decay are shown in Fig. 4c with dark dots. In Fig. 4d shows the complete half-lives. For even-even nuclei located inside the central contour, they are ~10 5 years. Thus, after taking into account all types of decay, it turns out that nuclei in the vicinity of Z = 110 and N = 184 form an “island of stability.” The 294 110 nucleus has a half-life of about 10 9 years. The difference between the Z value and the magic number 114 predicted by the shell model is due to competition between fission (relative to which the nucleus with Z = 114 is most stable) and α-decay (relative to which nuclei with lower Z are stable). For odd-even and even-odd nuclei, the half-lives increase with respect to α-decay and spontaneous fission, and decrease with respect to β-decay. It should be noted that the above estimates strongly depend on the parameters used in the calculations and can only be considered as indications of the possibility of the existence of superheavy nuclei with lifetimes long enough for their experimental detection. The results of another calculation of the equilibrium shape of superheavy nuclei and their half-lives are shown in Fig. 5, 11.11. In Fig. Figure 11.10 shows the dependence of the equilibrium deformation energy on the number of neutrons and protons for nuclei with Z = 104-120. The deformation energy is defined as the difference between the energies of nuclei in equilibrium and spherical form. From these data it is clear that in the region Z = 114 and N = 184 there should be nuclei that have a spherical shape in the ground state. All superheavy nuclei discovered to date (they are shown in Fig. 5 as dark diamonds) are deformed. Light diamonds show nuclei that are stable with respect to β-decay. These nuclei must decay by α decay or fission. The main decay channel should be α-decay. The half-lives for even-even β-stable isotopes are shown in Fig. 6. According to these predictions, half-lives are expected for most nuclei much longer than those observed for already discovered superheavy nuclei (0.1-1 ms). For example, for the 292110 nucleus, a lifetime of ~51 years is predicted. Thus, according to modern microscopic calculations, the stability of superheavy nuclei increases sharply as they approach the neutron magic number N = 184. Until recently, the only isotope of an element with Z = 112 was the isotope 277 112, which has a half-life of 0.24 ms. The heavier isotope 283112 was synthesized in the cold fusion reaction 48 Ca + 238 U. Irradiation time 25 days. The total number of 48 Ca ions on the target is 3.5·10 18. Two cases were recorded that were interpreted as spontaneous fission of the resulting isotope 283 112. The half-life of this new isotope was estimated at T 1/2 = 81 s. Thus, it is clear that an increase in the number of neutrons in the isotope 283112 compared to the isotope 277112 by 6 units increases the lifetime by 5 orders of magnitude. In Fig. Figure 7 shows the measured lifetime of seaborgium isotopes Sg (Z = 106) in comparison with the predictions of various theoretical models. Noteworthy is the decrease in the lifetime of the isotope with N = 164 by almost an order of magnitude compared to the lifetime of the isotope with N = 162. The closest approach to the island of stability can be achieved in the reaction 76 Ge + 208 Pb. A superheavy almost spherical nucleus can be formed in a fusion reaction followed by the emission of γ quanta or a single neutron. According to estimates, the resulting 284 114 nucleus should decay with the emission of α particles with a half-life of ~ 1 ms. Additional information about the occupancy of the shell in the region N = 162 can be obtained by studying the α-decays of nuclei 271 108 and 267 106. Half-lives of 1 min are predicted for these nuclei. and 1 hour. For nuclei 263 106, 262 107, 205 108, 271,273 110 isomerism is expected, the reason for which is the filling of subshells with j = 1/2 and j = 13/2 in the region N = 162 for nuclei deformed in the ground state. In Fig. Figure 8 shows the experimentally measured excitation functions for the formation reaction of the elements Rf (Z = 104) and Hs (Z = 108) for the fusion reactions of incident ions 50 Ti and 56 Fe with a target nucleus 208 Pb. The resulting compound nucleus is cooled by the emission of one or two neutrons. Information about the excitation functions of heavy ion fusion reactions is especially important for obtaining superheavy nuclei. In the fusion reaction of heavy ions, it is necessary to precisely balance the effects of Coulomb forces and surface tension forces. If the energy of the incident ion is not high enough, then the minimum approach distance will not be sufficient for the merger of the binary nuclear system. If the energy of the incident particle is too high, then the resulting system will have a high excitation energy and will most likely disintegrate into fragments. Effective fusion occurs in a rather narrow energy range of colliding particles. Fusion reactions with the emission of a minimum number of neutrons (1-2) are of particular interest, because in synthesized superheavy nuclei, it is desirable to have the largest possible N/Z ratio. In Fig. Figure 9 shows the fusion potential for nuclei in the reaction 64 Ni + 208 Pb 272 110. The simplest estimates show that the probability of the tunneling effect for nuclear fusion is ~ 10 -21, which is significantly lower than the observed value of the cross section. This can be explained as follows. At a distance of 14 fm between the centers of the nuclei, the initial kinetic energy of 236.2 MeV is completely compensated by the Coulomb potential. At this distance, only nucleons located on the surface of the nucleus are in contact. The energy of these nucleons is low. Therefore, there is a high probability that nucleons or pairs of nucleons will leave the orbitals in one nucleus and move to the free states of the partner nucleus. The transfer of nucleons from an incident nucleus to a target nucleus is especially attractive in the case when the doubly magic lead isotope 208 Pb is used as a target. In 208 Pb the proton subshell h 11/2 and the neutron subshells h 9/2 and i 13/2 are filled. Initially, the transfer of protons is stimulated by proton-proton attractive forces, and after filling the h 9/2 subshell - by proton-neutron attractive forces. Similarly, neutrons move into the free subshell i 11/2, attracted by neutrons from the already filled subshell i 13/2. Due to the pairing energy and large orbital angular moments, the transfer of a pair of nucleons is more likely than the transfer of a single nucleon. After the transfer of two protons from 64 Ni 208 Pb, the Coulomb barrier decreases by 14 MeV, which promotes closer contact of interacting ions and the continuation of the nucleon transfer process. In the works of [V.V. Volkov. Nuclear reactions of deep inelastic transfers. M. Energoizdat, 1982; V.V. Volkov. Izv. USSR Academy of Sciences, physical series, 1986, vol. 50 p. 1879] the mechanism of the fusion reaction was studied in detail. It is shown that already at the capture stage, a double nuclear system is formed after the complete dissipation of the kinetic energy of the incident particle and the nucleons of one of the nuclei are gradually transferred, shell by shell, to the other nucleus. That is, the shell structure of the nuclei plays a significant role in the formation of the compound core. Based on this model, it was possible to describe quite well the excitation energy of compound nuclei and the cross section for the formation of 102-112 elements in cold fusion reactions. At the Laboratory of Nuclear Reactions named after. G.N. Flerov (Dubna) synthesized an element with Z = 114. The reaction was used Identification of the 289 114 nucleus was carried out using a chain of α decays. Experimental assessment of the half-life of the isotope 289 114 ~30 s. The obtained result is in good agreement with previously performed calculations. When synthesizing element 114 in the reaction 48 Cu + 244 Pu, the maximum yield is obtained by the channel with the evaporation of three neutrons. In this case, the excitation energy of the compound nucleus 289 114 was 35 MeV. The theoretically predicted sequence of decays occurring with the 296 116 nucleus formed in the reaction is shown in Fig. 10. Rice. 10. Scheme of nuclear decay 296 116 The 296 116 nucleus is cooled by the emission of four neutrons and turns into the isotope 292 116, which then, with a 5% probability, as a result of two successive e-captures turns into the isotope 292 114. As a result of α-decay (T 1/2 = 85 days), the isotope 292 114 turns into the isotope 288 112. The formation of the isotope 288 112 also occurs through the channel The final nucleus 288 112 resulting from both chains has a half-life of about 1 hour and decays by spontaneous fission. With approximately a 10% probability, as a result of the α-decay of the isotope 288 114, the isotope 284 112 can be formed. The above periods and decay channels were obtained by calculation. When analyzing the various possibilities for the formation of superheavy elements in reactions with heavy ions, the following circumstances must be taken into account. It is necessary to create a nucleus with a sufficiently large ratio of the number of neutrons to the number of protons. Therefore, heavy ions with a large N/Z must be chosen as the incident particle. It is necessary that the resulting compound nucleus have a low excitation energy and a small angular momentum, since otherwise the effective height of the fission barrier will decrease. It is necessary that the resulting nucleus has a shape close to spherical, since even a slight deformation will lead to rapid fission of the superheavy nucleus. A very promising method for producing superheavy nuclei are reactions such as 238 U + 238 U, 238 U + 248 Cm, 238 U + 249 Cf, 238 U + 254 Es. In Fig. Figure 11 shows the estimated cross sections for the formation of transuranium elements upon irradiation of targets consisting of 248 Cm, 249 Cf and 254 Es with accelerated 238 U ions. In these reactions, the first results on the cross sections for the formation of elements with Z > 100 have already been obtained. To increase the yields of the reactions under study, the target thicknesses were chosen in such a way that the reaction products remained in the target. After irradiation, individual chemical elements were separated from the target. α-decay products and fission fragments were recorded in the samples obtained over several months. Data obtained using accelerated uranium ions clearly indicate an increase in the yield of heavy transuranium elements compared to lighter bombarding ions. This fact is extremely important for solving the problem of fusion of superheavy nuclei. Despite the difficulties of working with appropriate targets, forecasts for progress towards high Z look quite optimistic. Advances in the field of superheavy nuclei in recent years have been stunningly impressive. However, so far all attempts to discover the island of stability have not been successful. The search for him continues intensively.