Region Of Superheavy Nuclei Research Articles

Nuclear Data Sheets for A=267,271,275,279,283,287,291,295,299

Information on the production, identification, half-lives and decay modes for experimentally known nuclides with mass numbers of 267, 271, 275, 279, 283, 287, and 291, along with attempts to observe nuclides with mass numbers of 295 and 299, are presented along with the recommended values. Data here supersede data from the previous evaluation in this region, 2005Gu33. Since the previous evaluation many new and conclusive experiments have explored the region of superheavy nuclei, thus significantly expanding our knowledge of the nuclear chart in this area.

Nuclear Data Sheets for A=269,273,277,281,285,289, and 293

Information on the production, identification, half-lives and decay modes for experimentally known nuclides with mass numbers of 269, 273, 277, 281, 285, 289, and 293 are presented along with the recommended values. Data here supersede data from the previous evaluation in this region, 2005Gu33. Since the previous evaluation many new and conclusive experiments have explored the region of superheavy nuclei, thus significantly expanding our knowledge of the nuclear chart in this area.

Investigation of alpha decay half-lives within a modified Woods–Saxon potential

The predictive accuracy of the unified fission model based on a modified Woods–Saxon potential (UFMWS) is assessed by systematically calculating the decay half-lives of alpha emitters from [Formula: see text] to [Formula: see text]. The computed results are compared with recent experimental data as well as with results obtained using different semi-empirical formulas. After confirming the performance of the UFMWS, we focus on the alpha decay of even-Z superheavy nuclei with [Formula: see text]. The comparison between the experimental and the theoretical alpha-decay energies extracted from four different mass tables as well as between the experimental half-lives and those calculated by UFMWS using the theoretical values have shown that the WS4 mass model is the most accurate in the region of superheavy nuclei. The alpha decay half-lives of the nuclei of interest have then been computed with the UFMWS by inputting the WS4 decay energies. The study of the neutron number variation of decay half-lives allowed to identify regions of increased stability and to predict neutron magic numbers.

Calculated fission-fragment mass yields and average total kinetic energies of heavy and superheavy nuclei

Fission-fragment mass and total-kinetic-energy (TKE) distributions following fission of even-even nuclides in the region 74 le Z le 126 and 92 le N le 230, comprising 896 nuclides have been calculated using the Brownian shape-motion method. The emphasis is the region of superheavy nuclei. To show compatibility with earlier results the calculations are extended to include earlier studied regions. An island of asymmetric fission is obtained in the superheavy region, 106le Zle 114 and 162le Nle 176, where the heavy fragment is found to be close to ^{208}Pb and the light fragment adjusts accordingly. Most experimentally observed alpha -decay chains of superheavy nuclei with Z > 113 terminate by spontaneous fission in our predicted region of asymmetric fission. In these cases, the pronounced large asymmetry is accompanied by a low TKE value compatible with measurements.

Capture and fission analysis of various superheavy isotopes with ACN = 258–280

The capture and fission analysis of heavy ion induced fusion reactions leading to the formation of Z = 107–111 superheavy nuclei has been carried out. Attempts have been made to analyze the synthesis traits, such as excitation functions, formation probabilities, barrier characteristics etc. The ℓ-summed Wong model provides a decent description of available data on capture (σCap) and fusion-fission (σff) cross-sections and hence is exploited to make relevant predictions for future experiments. The capture and fusion-fission excitation functions are predicted for the least explored region of superheavy nuclei (SHN) i.e. Z = 107–111. The role of mass-asymmetry (η), Coulomb factor (ZPZT), deformation and orientations, Businari-Gallone mass-asymmetry (αBG), fission barrier (Bf) etc is duly explored. The present study concludes that the mass-asymmetric reactions involving 24Mg, 30Si, and 36S projectiles are preferred for the synthesis of unknown isotopes of Z = 107–111. Alternatively, the doubly magic 48Ca-projectile also provides a competing alternative to produce neutron-rich isotopes of the above-mentioned SHN.

The role of ion sources in synthesis of the super-heavy elements.

Since the early 1970s, attempts to synthesize Super Heavy Elements (SHE) have been made in many laboratories around the world. One of the main requirements of these experiments is a sufficiently large dose of target irradiation, which should be increased with a decrease in the reaction cross section. In this regard, the capacities of ion sources play an important role for the successful synthesis of SHE. At the FLNR JINR, the discovery and investigation of the new region of super heavy nuclei were based on fusion reactions of 48Ca with 238U-249Cf target nuclei. In these experiments, a technique for the production of metallic 48Ca was developed. The operation mode of the ECR ion source was set to optimize the intensity of 48Ca ions and attain maximum ionization efficiency. Because of the heaviest target for experiments on synthesis of SHE in heavy ion reactions is 249Cf, so further progress in the synthesis of elements with Z > 118 requires the production of intense beams of accelerated neutron enriched isotopes, such as 50Ti, 58Fe, and 64Ni.

Restoration of Wigner’s Sypersymmetry in Heavy and Superheavy Nuclei

Various aspects of restoration of Wigner’s supersymmetry [SU(4) symmetry] in heavy and superheavy nuclei are analyzed by comparing the results of calculations with experimental data. The energy differences between the giant Gamow–Teller and analog resonances ($$E_{\mathrm{G}}$$ and $$E_{\mathrm{A}}$$) are given according to calculations within the theory of finite Fermi systems for 34 nuclei for which experimental data are known. The calculated energy differences $$\Delta E_{\mathrm{G{-}A}}$$ of $$E_{\mathrm{G}}$$ and $$E_{\mathrm{A}}$$ tend to zero in heavier nuclei, demonstrating the restoration of Wigner’s SU(4) symmetry. Also, the isotopic dependence of the Coulomb energy difference between neighboring nuclear isobars is analyzed within the SU(4) approach for more than 400 nuclei in the mass-number range of $$A=5{-}244$$. The restoration of Wigner’s SU(4) symmetry in heavy nuclei is confirmed. It is shown that the restoration of Wigner’s SU(4) symmetry is compatible with the possible existence of an island of stability in the region of superheavy nuclei.

Studies on the Existence of Various 1p, 2p Halo Isotopes via Cluster Decay of Nuclei in Superheavy Region

The 1p and 2p halo structures of various halo candidates are identified from the separation energy calculations and driving potential curves. 11N, 23Al, and 26,27,28P are belonging to the 1p halo structure with low S(p) than S(2p) but 27,28,29S shows 2p halo structure. The decay possibilities of the 1p halo nuclei 8B, 11,12N, 17F, 23Al, and 26,27,28P and 2p halo nuclei 9C, 17,18Ne, 20Mg, and 28,29S from the superheavy parent isotopes with Z = 103 to 114 are studied within the Coulomb and Proximity Potential Model by evaluating the decay half-lives. Plots connecting the half-life for the emission of proton halos with the neutron number of daughter nuclei give the evidence for the possibility for the existence of the selected halo nuclei. It is evident from the computed half-lives that the emission of 1p halo nuclei such as 8B, 12N, and 17F and 2p halo nucleus 18Ne from various superheavy isotopes is probable. The plot connecting computed half-lives versus neuron number of the daughter nuclei indicates the nuclear shell closure effect of parent and daughter nuclei at N=126, 132, and 138

Attempt to connect the nuclear charge radii with the experimental α decay data for superheavy nuclei

Significant progresses have been made so far for the synthesis of the heaviest elements, while the knowledge of them appears to be quite limited even when it comes to basic properties, e.g., their size. On the other side, the observation of α decay chains is the main tool to identify the newly produced elements. In this report, we propose to make use of the available experimental α decay data to extract the nuclear charge radii of superheavy nuclei. Within the density dependent cluster model, the nucleon density distribution of the target nucleus is determined by exactly reproducing the measured α decay half-life of its parent, finally leading to the nuclear radii. Encouraged by the agreement between theory and experiment for heavy nuclei, we extend the study to the region of superheavy nuclei as well.

Pre-scission model predictions of fission fragment mass distributions for super-heavy elements

The total deformation energy just before the moment of neck rupture for the heaviest nuclei for which spontaneous fission has been detected (Ds279–281, Rg281 and Cn282–284) is calculated. The Strutinsky's prescription is used and nuclear shapes just before scission are described in terms of Cassinian ovals defined for the fixed value of elongation parameter α=0.98 and generalized by the inclusion of four additional shape parameters: α1, α3, α4, and α6. Supposing that the probability of each point in the deformation space is given by Boltzmann factor, the distribution of the fission-fragment masses is estimated. The octupole deformation α3 at scission is found to play a decisive role in determining the main feature of the mass distribution: symmetric or asymmetric. Only the inclusion of α3 leads to an asymmetric division. Finally, the calculations are extended to an unexplored region of super-heavy nuclei: the even–even Fl (Z=114), Lv (Z=116), Og (Z=118) and (Z=126) isotopes. For these nuclei, the most probable mass of the light fragment has an almost constant value (≈136) like in the case of the most probable mass of the heavy fragment in the actinide region. It is the neutron shell at 82 that makes this light fragment so stable. Naturally, for very neutron-deficient isotopes, the mass division becomes symmetric when N=2×82.

Charge-exchange resonances and restoration of Wigner’s supersymmetry in heavy and superheavy nuclei

Various facets of the question of whether Wigner’s supersymmetry [SU(4) symmetry] may be restored in heavy and superheavy nuclei are analyzed on the basis of a comparison of the results of calculations with experimental data. The energy difference between the giant Gamow–Teller resonance and the analog resonance (the difference of E G and E A) according to calculations based on the theory of finite Fermi systems is presented for the case of 33 nuclei for which experimental data are available. The calculated difference ΔE G–A of E G and E A tends to zero in heavier nuclei, showing evidence of the restoration of Wigner’s SU(4) symmetry. Also, the isotopic dependence of the Coulomb energy difference between neighboring isobaric nuclei is analyzed within the SU(4) approach for more than 400 nuclei in the mass-number range of A = 5–244. The restoration of Wigner’s SU(4) symmetry in heavy nuclei is confirmed. It is shown that the restoration of SU(4) symmetry is compatible with the possible existence of the stability island in the region of superheavy nuclei.

Charge-exchange resonances and restoration of the Wigner SU(4)-symmetry in heavy and superheavy nuclei

Energies of the giant Gamow-Teller and analog resonances - $E_{\rm G}$ and $E_{\rm A}$, are presented, calculated using the microscopic theory of finite Fermi system. The calculated differences $\Delta E_{\rm G-A}=E_{\rm G}-E_{\rm A}$ go to zero in heavier nuclei indicating the restoration of Wigner SU(4)-symmetry. The calculated $\Delta E_{\rm G-A}$ values are in good agreement with the experimental data. The average deviation is 0.30 MeV for the 33 considered nuclei for which experimental data is available. The $\Delta E_{\rm G-A}$ values were calculated for heavy and superheavy nuclei up to the mass number $A $= 290. Using the experimental data for the analog resonances energies, the isotopic dependence of the difference of the Coulomb energies of neighboring nuclei isobars analyzed within the SU(4)-approach for more than 400 nuclei in the mass number range of $A$ = 3 - 244. The Wigner SU(4)-symmetry restoration for heavy and superheavy nuclei is confirmed. It is shown that the restoration of SU(4)-symmetry does not contradict the possibility of the existence of the "island of stability" in the region of superheavy nuclei.

Nuclear structure of elements with 100 ≤ Z ≤ 109 from alpha spectroscopy

Significant technical progress concerning the availability of intense heavy-ion beams and highly-efficient and sophisticated detection devices has made nuclear-structure investigations possible in the region of superheavy nuclei. Exciting new results have been obtained by applying α spectroscopy as well as α–γ and internal-conversion-electron coincidence spectroscopy. The present review article gives an overview of the experimental techniques and methods with specific attention to the recent developments of digital signal and data processing giving access to half-life ranges of less than a few microseconds. The presentation of the experimental results and the physics discussion will be focused on nuclear structure systematics in even-Z nuclei along the N=151,153,and155 isotonic lines, where most progress has been achieved in the last 10 years.

Superheavy nuclei from 48Ca-induced reactions

The discovery and investigation of the new region of superheavy nuclei at the DGFRS separator based on fusion reactions of 48Ca with 238U–249Cf target nuclei are reviewed. The production cross sections and summaries of the decay properties, including the results of the posterior experiments performed at the SHIP, BGS, and TASCA separators, as well as at the chemistry setups, are discussed and compared with the theoretical calculations and the systematic trends in the α-decay and spontaneous fission properties. The properties of the new nuclei, isotopes of elements 112–118, and their decay products demonstrate significant increases in the stability of the heaviest nuclei with increasing neutron number and closer approach to magic number N=184.

Restoration of Wigner supersymmetry in heavy and superheavy nuclei

The possibility of the restoration of Wigner supersymmetry (SU(4) symmetry) in heavy and superheavy nuclei has been analyzed by comparing the calculations with experimental data. The differences between the energies of the giant Gamow–Teller resonance (EG) and analog resonance (EA) calculated within the finite Fermi system theory for 33 nuclei for which experimental data exist are presented. The energy differences ΔEG–A between EG and EA tend to zero in heavier nuclei, demonstrating the restoration of Wigner SU(4) symmetry. The energy differences ΔEG–A have also been calculated for heavy and superheavy nuclei located on the betastability line in the mass number range of A = 140–290. In the SU(4) approach, the isotopic dependence of the difference between the Coulomb energies of neighboring isobar nuclei has been analyzed for more than 400 nuclei in the mass number range of A = 3–244. The restoration of Wigner SU(4) symmetry in heavy and superheavy nuclei has been confirmed. It has been shown that the restoration of SU(4) symmetry does not contradict the possibility of the existence of the “island of stability” in the region of superheavy nuclei.

Study of multi-nucleon transfer reactions in 58, 64Ni + 207Pb collisions at the velocity filter SHIP

We investigated multi-nucleon transfer reactions in collisions of 58Ni + 207Pb and 64Ni + 207Pb at Coulomb barrier energies. The new aspect is that we used a velocity filter (SHIP at GSI) for the separation of the heavy target-like transfer products from background events. The isotopic identification was performed via the $ \alpha$ decay properties of the reaction products. The goal of the experiment was to study the characteristics of multi-nucleon transfer reactions in the region of heavy nuclei and the applicability of existing separation and detection techniques, which are usually used for identification of heavy fusion-evaporation residues, to heavy transfer products. This was motivated by recent theoretical results from macroscopic-microscopic models which suggest deep inelastic transfer reactions in heavy systems as a means to produce new neutron-rich isotopes in the region of N = 126 and in the region of superheavy nuclei. In this paper we present the isotopic yields, the excitation functions and the excitation energies of the heavy transfer products with Z > 82 as well as the influence of shell effects on the reaction products. The influence of the different neutron numbers of the projectiles is also discussed.

Population of rotational bands in superheavy nuclei

Using the statistical approach, we study the population of ground-state rota- tional bands of superheavy nuclei produced in the fusion-evaporation reactions 208 Pb( 48 Ca, 2n) 254 No, 206 Pb( 48 Ca, 2n) 252 No, and 204 Hg( 48 Ca, 2n) 250 Fm. We calculate relative intensi- ties of E2-transitions between the rotational states and entry spin distributions of the resid- ual nuclei, evaporation residue cross sections, and excitation functions for these reactions. Fermi-gas model is used for the calculation of level density, and damping of shell effects both with excitation energy and angular momentum is taking into account. The results are in a good agreement with the experiment data. theoretical approaches which predict the next doubly magic shell closure beyond 208 Pb. Reaching the region of superheavy nuclei in the vicinity of this closure, so called island of stability, is a challenge for the modern nuclear physics. The macroscopic-microscopic approaches predict the magic nucleus with Z=114 (1). The closed shell Z = 114 disappears in the framework of self-consistent mean-field models (2-6) which result the strong shell effects at Z=120-126. Although all these models provide close binding energies for nuclei with Z �114, their predictions for the spins of the ground states, quasiparticle spectra, and for the moments of inertia are rather different. Therefore, one can test the theoretical models by comparing their structure predictions with the spectroscopical data. Experimental study of rotational bands of superheavies is especially hopeful, as the limits of sta- bility of these nuclei in spin and excitation energy are governed by the fission barrier, which is mostly defined by shell component. The investigation of high-spin spectra also provides information about angular momentum dependence of the shell effects. Unfortunately, there are still a little experimental data for the heaviest evaporation residues, as their production cross sections are too small for the spec- troscopical analysis. However, using the in-beam studies, the structure of high-spin excited states up to � 20~ has been recently identified for the nuclei 254 No, 252 No, and 250 Fm, produced with the cross sections 0.2-3 µb (7-10). The nuclei studied are produced in fusion-evaporation reactions, which can be successfully de- scribed using the statistical approach. In Refs. (11-14) we have already calculated evaporation residue cross sections and excitation functions for superheavy isotopes using their properties, predicted by different theoretical models (15-18). The results are in a good agreement with the experimental data. In the present paper, we extend the statistical approach to describe the population of yrast rotational states in the residual superheavy nuclei and the production of evaporation residues in the complete fusion reactions 206,208 Pb( 48 Ca, 2n) 252,254 No and 204 Hg( 48 Ca, 2n) 250 Fm, taking into consideration the survival of compound nuclei against fission at di fferent angular momenta. The relative intensities of E2-transitions and entry spin distributions of the residual nuclei can be derived from the calculated population cross sections of the rotational states and compared with the experimental data (7-10).

SPONTANEOUS FISSION HALF-LIVES IN VARIOUS MACROSCOPIC-MICROSCOPIC MODELS

The problem of describing spontaneous fission for the entire region of superheavy nuclei is continually present in theoretical investigations. This study outlines the results of the calculations of fission barriers and spontaneous fission half-lives for superheavy nuclei in the region of Z =100-122 using a mean field model. We examine four distinct macroscopic models and two types of pairing interactions. Our approach is based on the deformed Woods-Saxon potential. Spontaneous fission half-lives are calculated using a multi-dimensional dynamical-programming method, where the action integral is minimized within a three dimensional deformation space (β2, β4, β6).

Nuclear structure investigations in the region of superheavy nuclei

Radioactive decay from the ground state or isomeric states has been investigated for a series of nuclei in the region of Z = 100–106 by means of α–γ—or evaporation residue-(γ, conversion electron)—measurements in prompt and delayed coincidence. Systematic trends in single-particle level energies in N = 145–151 odd-even isotones could be extended up to Z = 104, while an energy systematics of lowlying Nilsson levels in odd-mass einsteinium isotopes was established. Information on nuclear levels at E* > 500 keV was obtained from the decay study of isomeric states in 251−255No.

Shell corrections, magic numbers, and mean field

It is shown that the positions of deep local minima of shell corrections associated with magic numbers in the region of superheavy nuclei depend on the parameters of the central and spin-orbit mean-field potentials. The accuracy of nuclear-mass predictions made within various models for superheavy nuclei is analyzed.