Stability Of Superheavy Nuclei Research Articles

On the stability of superheavy nuclei

Potential energy surfaces of even–even superheavy nuclei are evaluated within the macroscopic-microscopic approximation. A very rapidly converging analytical Fourier-type shape parametrization is used to describe nuclear shapes throughout the periodic table, including those of fissioning nuclei. The Lublin Strasbourg Drop and another effective liquid-drop type mass formula are used to determine the macroscopic part of nuclear energy. The Yukawa-folded single-particle potential, the Strutinsky shell-correction method, and the BCS approximation for including pairing correlations are used to obtain microscopic energy corrections. The evaluated nuclear binding energies, fission-barrier heights, and \(Q_\alpha \) energies show a relatively good agreement with the experimental data. A simple one-dimensional WKB model à la Świa̧tecki is used to estimate spontaneous fission lifetimes, while \(\alpha \) decay probabilities are obtained within a Gamow-type model.

Stability of superheavy nuclei

The potential-energy surfaces of an extended set of heavy and super-heavy even-even nuclei with $92 \le Z \le 126$ and isospins $40 \le N-Z \le 74$ are evaluated within the recently developed Fourier shape parametrization. Ground-state and decay properties are studied for 324 different even-even isotopes in a four-dimensional deformation space, defined by non-axiality, quadrupole, octupole, and hexadecapole degrees of freedom. Nuclear deformation energies are evaluated in the framework of the macroscopic-microscopic approach, with the Lublin-Strasbourg-Drop model and a Yukawa-folded mean-field potential. The evolution of the ground-state equilibrium shape (and possible isomeric, metastable states) is studied as a function of $Z$ and $N$. Alpha-decay $Q$-values and half-lives, as well as fission-barrier heights, are deduced. In order to understand the transition from asymmetric to symmetric fission along the Fm isotopic chain, the properties of all identified fission paths are investigated. Good agreement is found with experimental data wherever available. New interesting features about the population of different fission modes for nuclei beyond Fm are predicted.

Stability of super heavy nuclei associated with the updated nuclear data**Supported by National Natural Science Foundation of China (11675066, 11647306), Fundamental Research Funds for the Central Universities (lzujbky-2017-ot04) and Feitian Scholar Project of Gansu province

The stability of super heavy nuclei (SHN) from Z=104 to Z=126 is analyzed systematically, associated with the following theoretical mass tables: FRDM2012 [At. Data Nucl. Data Tables 109-110(2016)], WS2010 [Phys. Rev. C 82, 044304(2010)], WS-LZ-RBF [J. Phys. G: Nucl. Part. Phys. 42, 095107(2015)] and the updated experimental data AME2016 [Chinese Physics C 41, 040002(2017)]. The nucleus with the biggest mean binding energy in each isotopic chain shows systematic regular behavior, indicating that the mean binding energy is a good criterion to classify SHN by their stability. Based on binding energy, the α-decay energy Qα, two-proton separation energy S2p, and two-neutron separation energy S2n are extracted and analyzed. It is found that N=152 and N=162 are sub-magic numbers, N = 184 is a neutron magic number, and Z = 114 is a proton magic number, which may provide useful information for the synthesis and identification of SHN.

Ternary fission of superheavy elements

Ternary fission of superheavy nuclei is studied within the three-cluster model potential energy surfaces (PESs). Due to shell effects, the stability of superheavy nuclei has been predicted to be associated with $Z=114$, 120, and 126 for protons and $N=184$ for neutrons. Taking some representative nuclei we have extended the ternary fission studies to superheavy nuclei. We adopted two minimization procedures to minimize the potential and considered different arrangements of the fragments. The PES from one-dimensional minimization reveals a strong cluster region favoring various ternary breakups for an arrangement in which the lightest fragment is kept at the center. The PES obtained from two-dimensional minimization reveals strong preference of ternary fragmentation in the true ternary fission region. Though the dominant decay mode of superheavy nuclei is $\ensuremath{\alpha}$ decay, the $\ensuremath{\alpha}$-accompanied ternary breakup is found to be a nonfavorable one. Further, the prominent ternary combinations are found to be associated with the neutron magic number.

The discovery of elements 113 to 118

Discovery and investigation of the “Island of stability” of superheavy nuclei at the separator DGFRS in the 238 U- 249 Cf+ 48 Ca reactions is reviewed. The results are compared with the data obtained in chemistry experiments and at the separators SHIP, BGS, TASCA, and GARIS. The synthesis of the heaviest nuclei, their decay properties, and methods of identification are discussed and compared with the criteria that must be satisfied for claiming the discovery of a new chemical element. The role of shell effects in the stability of superheavy nuclei is demonstrated by comparison of the experimental results with empirical systematics and theoretical data.

Stability of superheavy nuclei against α-decay and spontaneous fission

The stability of superheavy nuclei is mainly determined by the competition between alpha-decay and spontaneous fission. We investigate the half-lives of both alpha-decay and spontaneous fission for the heaviest nuclei with proton numbers up to Z = 121. The agreement between theoretical half-lives and available experimental data is fairly well for the superheavy nuclei. Enhanced stability against spontaneous fission is found for the Z = 119 and Z = 120 isotopic chains, which are of current experimental interests, alpha-Decay is predicted to be the dominating decay mode for the Z = 119 and Z = 120 isotopes with estimated half-lives ranging from microseconds to milliseconds. (c) 2012 Elsevier B.V. All rights reserved.

Correlation betweenα-Decay Energies of Superheavy Nuclei Involving the Effects of Symmetry Energy

A formula for the relationship between the α-decay energies (Q values) of superheavy nuclei (SHN) is presented, which is composed of the effects of Coulomb energy and symmetry energy. It can be employed not only to validate the experimental observations and measurements to a large extent, but also to predict the Q values of heaviest SHN with a high accuracy generally which will be very useful for future experiments. Furthermore, the shell closures in superheavy region and the effect of the symmetry energy on the stability of SHN against α decay are discussed with the help of this formula.

Discovery of the New Element Z=117 and Confirmation of 115

The discovery of the new chemical element with atomic number Z=117 is presented. The isotopes 293 117 and 294 117were produced in fusion reactions between 48 Ca and 249 Bk. The 249 Bk was produced in the High Flux Isotope Reactor and chemically separated at Oak Ridge. Decay chains involving eleven new nuclei were identified by means of the Dubna Gas-Filled Recoil Separator. The measured decay properties show a strong rise of stability for superheavy nuclei toward N=184.The reaction 243 Am+ 48 Ca was studied at three energies. Twenty one decay chains of 288 115 and one decay chain of 289 115 were observed to confirm the earlier discoveries of Z=115 and 117.

Analytic expressions forαparticle preformation in heavy nuclei

Experimental $\ensuremath{\alpha}$ decay energies and half-lives are investigated systematically to extract $\ensuremath{\alpha}$ particle preformation in heavy nuclei. Formulas for the preformation factors are proposed that can be used to guide microscopic studies on preformation factors and perform accurate calculations of the $\ensuremath{\alpha}$ decay half-lives. There is little evidence for the existence of an island of long stability of superheavy nuclei.

REVIEW ON THEORETICAL STUDIES OF SUPERHEAVY NUCLEI

Superheavy elements have provided a good test of the validity of both nuclear structure models and nuclear decay models in a large mass region. We firstly review the recent progress on theoretical studies of superheavy nuclei. Emphasis is placed on the structure and decay of superheavy nuclei. Then theoretical results of odd-odd nuclei with Z = 109 - 115 are presented and discussed. It is clearly demonstrated that there is shape coexistence for the ground state of many superheavy nuclei from different models and many superheavy nuclei are deformed. In some cases superdeformation can become the ground state of superheavy nuclei and it is important for future studies of superheavy nuclei. This can lead to the existence of low-energy isomers in the superheavy region and it plays an important role for the stability of superheavy nuclei. As α-decay and spontaneous fission plays a crucial role for identifications of new elements, we also review some typical models of α-decay half-lives and spontaneous fissions half-lives. Some new views on superheavy nuclei are presented.

Synthesis of elements 115 and 113 in the reactionAm243+Ca48

The results of two experiments designed to synthesize element 115 isotopes in the {sup 243}Am+{sup 48}Ca reaction are presented. Two new elements with atomic numbers 113 and 115 were observed for the first time. With 248-MeV {sup 48}Ca projectiles, we observed three similar decay chains consisting of five consecutive {alpha} decays, all detected in a total time interval of 30 s. Each chain was terminated by a spontaneous fission (SF) with a high-energy release and a lifetime of about a day. With 253-MeV {sup 48}Ca projectiles, we registered a different decay chain of consecutive {alpha} decays detected in a time interval of 0.5 s, also terminated by spontaneous fission, but after 1.8 h. The decay properties of the eleven new {alpha}- and SF-decaying nuclei are consistent with expectations for consecutive {alpha} decays originating from the parent isotopes {sup 288}115 and {sup 287}115, produced in the 3n- and 4n-evaporation channels, respectively. Support for the assignment of the atomic numbers of all of the nuclei in the {sup 288}115 decay chain was obtained in an independent experiment in which a long-lived spontaneous fission activity, {sup 268}Db (15 events), was found to be chemically consistent with the fifth group of the periodic table.more » The odd-odd isotope {sup 288}115 was observed with largest cross section of about 4 pb. In the SF decay of {sup 268}Db, a total kinetic energy of 230 MeV and a neutron multiplicity per fission of 4.2 were measured. The decay properties of the 11 new isotopes with Z=105-115 and the production cross sections are in agreement with modern concepts of the role of nuclear shells in the stability of superheavy nuclei. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research.« less

Systematic Study of Stability of Super Heavy Nuclei**The project supported by National Natural Science Foundation of China under Grant Nos. 10175082, 10235020, and 10235030, the Major Basic Research Development Program under Grant No. G2000-0774-07, the Knowledge Innovation Project of the Chinese Academy of Sciences under Grant No. KJCX2-SW-N02, One Hundred Person Project of CSA, the State Key Basic Research Program

A systematic overview on the characteristics of super heavy nuclei from to based on the data by P. Möller et al. is presented. The nuclei which have the biggest mean binding energy in each of their isotope chain show systematic regular behavior, indicating that the mean binding energy is a good criterion to classify super heavy nuclei by their stabilities. Further investigation on the nuclear data at and after has been suggested.

Shell Effect of Superheavy Nuclei in Self-consistent Mean-Field Models**The project supported by National Natural Science Foundation of China under Grant No. 10125521, the 973 National Major Basic Research and Development Program of China under Grant No. G2000077400, and the Research Fund for the Doctoral Program of Higher Education under Contract No. 20010284036

We analyze in detail the numerical results of superheavy nuclei in deformed relativistic mean-field model and deformed Skyrme–Hartree–Fock model. The common points and differences of both models are systematically compared and discussed. Their consequences on the stability of superheavy nuclei are explored and explained. The theoretical results are compared with new data of superheavy nuclei from GSI and from Dubna and reasonable agreement is reached. Nuclear shell effect in superheavy region is analyzed and discussed. The spherical shell effect disappears in some cases due to the appearance of deformation or superdeformation in the ground states of nuclei, where valence nucleons occupy significantly the intruder levels of nuclei. It is shown for the first time that the significant occupation of valence nucleons on the intruder states plays an important role for the ground state properties of superheavy nuclei. Nuclei are stable in the deformed or superdeformed configurations. We further point out that one cannot obtain the octupole deformation of even-even nuclei in the present relativistic mean-field model with the σ, ω and ρ mesons because there is no parityviolating interaction and the conservation of parity of even-even nuclei is a basic assumption of the present relativistic mean-field model.

Mechanism behind the relation between shell structure and stability of heaviest nuclei

Mechanisms behind the relation between shell structure and stability of superheavy nuclei is discussed. The discussion is concentrated on the static spontaneous-fission barriers, calculated for these nuclei within a macroscopic-microscopic model.

Relativistic models for nuclear structure calculations: Comparative study of mean-field and Hartree-Fock approximation for superheavy nuclei

The relevance of exchange effects for the stability of superheavy nuclei is examined within a linear QHD-II model by comparing Hartree-Fock with meanfield results. To allow a scan of the complete superheavy regime the recently developed local density approximation (LDA) for the exchange potential is employed for the Hartree-Fock level calculations. It turns out that, while many nuclear properties obtained with the LDA approach differ significantly from the corresponding mean-field results, the predictions of the two methods for shell closures are very similar. Furthermore, a comparison with a nonlinear variant of QHD-II shows that many nuclear properties obtained with the LDA in the framework of linear QHD-II are somewhere in-between the corresponding linear and nonlinear mean-field results. This indicates that the LDA exchange partially includes nonlinear contributions, which supports the interpretation of the meson self-coupling as a parametrization of many-body effects.

Properties of the hypothetical spherical superheavy nuclei

Theoretical results on the ground-state properties of the hypothetical spherical superheavy atomic nuclei are presented and discussed. Even-even isotopes of elements Z=104{minus}120 are considered. Certain conclusions are also drawn for odd-A and odd-odd superheavy nuclei. Results obtained earlier for even-even deformed superheavy nuclei with Z=104{minus}114 are given for completeness. Equilibrium deformation, nuclear mass, {alpha}-decay energy, {alpha}-decay half-life, dynamical fission barrier, as well as spontaneous-fission half-life are considered. {beta}-stability of superheavy nuclei is also discussed. The calculations are based on the macroscopic-microscopic model. A multidimensional deformation space describing axially symmetric nuclear shapes is used in the analysis of masses and decay properties of superheavy nuclei. We determined the boundaries of the region of superheavy nuclei which are expected to live long enough to be detected after the synthesis in a present-day experimental setup. {copyright} {ital 1997} {ital The American Physical Society}

Fragmentation of the high spin discrete neutron and proton states of209Pb and209Bi

The distribution of the discrete 1h 9/2, 2f 7/2, 1i 13/2 and 2f 5/2 proton states of209Bi and 2g 9/2, 1i 11/2, 1j 15/2 and 2g7/2 neutron states of209Pb have been obtained within the particle-vibration coupling model calculation and compared with the experimental datas baising on the most recent high resolution stripping reaction on208Pb using 480 MeV12C projectile. The optimised shell model energies arising from the core-polarisation effect have profound influence for both the study of the structures of the high spin continuum shell model states of208Pb and stability of superheavy nuclei.

Pairing with a delta interaction in the energy density nuclear mass formula

Abstract The variations of the average pairing strength in the ( N , Z ) plane are studied with a δ-interaction in the frame of the self-consistent energy density formalism. It is found that the same δ-interaction with constant strength can be used for protons and neutrons in spherical nuclei near the stability line. This interaction is used to study the extrapolation of the average pairing strength to deformed nuclei, to the superheavy region and to the regions of the drip lines. The consequences of the results for the stability of superheavy nuclei and for magic numbers far from the stability region are examined.

On the Stability of Super-heavy Nuclei: Some Recent Results of Self-consistent Calculations

Self-consistent calculations of super-heavy elements are presented. The Skyrme effective interaction SIII has been used. This force gives an overall good fit of a wide range of nuclear properties, in particular for closed shell nuclei. The quality of these results puts reasonable limits on the reliability of extrapolation to unknown nuclei. Qα and Qβ values are calculated and corresponding lifetimes are estimated. For the nucleus 298114, the fission barrier has been obtained by a constrained self-consistent calculation.

On the Stability of Superheavy Nuclei against Fission, Alpha Decay and Electron Capture

Abstract The potential energy surface has been calculated by two methods which are compared with re­spect to spontaneous fission. In the first one essentially the sum of the single particle energies is computed as was done in a previous paper3 while in the second one the Strutinsky technique of renormalizing to a liquid drop model has been applied. Also the half-lives for electron capture are investigated together with the predictions of the half-lives for spontaneous fission and α-decay. The results support the existence of superheavy nuclei in the regions around Z = 114 and Z = 164.