Α-decay Chains Research Articles

Superheavy magic nuclei: Ground-state properties, bubble structure and α-decay chains

A systematic investigation of superheavy nuclei in the isotopic chains of proton numbers Z=106, 114, 120, and 126 together with isotonic chains of neutron numbers N=162, 172, and 184 is presented in the theoretical framework of relativistic mean-field density functionals based on density-dependent meson-nucleon couplings. Ground-state properties, including binding energy, shape, deformation, density profile, and radius, are estimated to provide compelling evidence of magicity in these even-even nuclei, aligning with the concept of the ‘island of stability.’ The analysis reveals central depletion in the charge density, indicating a bubble-like structure, primarily attributed to the substantial repulsive Coulomb field and the influence of higher l-states. A thorough examination of potential decay modes, employing various semi-empirical formulas, is presented. The probable α-decay chains are evaluated, demonstrating excellent agreement with available experimental data.

α-decay properties of superheavy nuclei with 117 ≤ Z ≤ 120 from the systematics of decay chains and isotopic chains* *Supported by the National Natural Science Foundation of China (12075121), the Natural Science Foundation of Jiangsu Province (BK20190067), and the Fundamental Research Funds for the Central Universities (30922010312)

Recently, the synthesis of new elements above Z = 118 has been a hot topic in nuclear physics. Meanwhile, the α-decay chain is expected to be the unique tool to identify these heaviest nuclei. We have systematically calculated the α-decay energies and half-lives on the same footing for superheavy nuclei (SHN) within the cluster model along with a slightly modified Woods-Saxon (W.S.) potential as the nuclear potential. Based on the available experimental data, the key radius parameter (R) in the α-core potential is determined via the systematic trend from the α-decay and isotopic chains. The α-decay energy ( ) values and half-lives are then obtained simultaneously for those unknown SHN in the range of 117 ≤ Z ≤ 120, during which the decay width is obtained using a new treatment for the asymptotic behavior of the α-core wave function. The theoretical values and experimental data are found to be in excellent agreement for the nuclei 117 and 118 regardless of the method used to determine the R parameter. Predicting the α-decay chains for new elements Z = 119 and Z = 120 can be useful in ongoing or forthcoming experiments.

Surface and decay properties of newly synthesized 207,208Th isotopes for various α-decay chains

Considering various initial deformations, the ground, first excited, and second excited states binding energies are calculated using the effective field theory motivated relativistic mean-field based IOPB-I force parameter. The alpha decay chains for both the 207Th and 208Th are examined. As observed for both nuclei, it takes four subsequent α-particle emissions to reach the stable Pb nucleus. The half-lives determined by two widely used Viola-Seaborg and modified universal decay law formulas are compared with the available experimental data. The surface property-like symmetry energy is also predicted for these nuclei in the framework of the coherent density fluctuation model and establishes a connection between the decay behavior and the symmetry energy.

Decay properties of undetected superheavy nuclei with Z > 110

A comprehensive study of favoured and unfavoured α-decay, cluster decay, weak-decay along with spontaneous fission in undetected superheavy nuclei within the range for proton number 111 ≤ Z ≤118 and neutron number 161 ≤ N ≤192 is performed. Half-lives for various mentioned decays are estimated with good accuracy on the basis of NUBASE2020 and are found in excellent match with the known half-lives. α-decay mode is found most probable in this wide range and correspondingly potential α-decay chains are reckoned. Peculiarly, the chances of cluster emission, as well as weak-decay, are also anticipated in this region of the periodic chart which open new pathways of detection of superheavy nuclei.

Theoretical predictions for α-decay chains and cluster radioactivity of superheavy nuclei with Z = 126

Theoretical predictions of [Formula: see text]-decay properties of several isotopes of the superheavy nucleus of [Formula: see text] [Formula: see text] and their consecutive [Formula: see text]-decay chains are presented. Based on the double-folding model, the [Formula: see text]–daughter interaction potential is constructed microscopically using a realistic M3Y–Paris nucleon–nucleon (NN) interaction. The [Formula: see text]-decay half-lives are computed for both spherical and deformed shapes of daughter nuclei within the density-dependent cluster model. The effect of deformation is found to decrease the [Formula: see text]-decay half-lives compared to spherical shapes. The calculated [Formula: see text]-decay half-lives are in satisfactory agreement with their counterparts using other theoretical methods. The prediction of the dominant decay mode for the isotopes [Formula: see text], which have not yet been experimentally synthesized, is presented through the competition between [Formula: see text]-decay and spontaneous fission. We have found that the isotopes [Formula: see text] survive fission and have relatively long half-lives which span the order [Formula: see text]–[Formula: see text]. Moreover, the correlation between the logarithm of the preformation probability deduced from the cluster formation model and the fragmentation potential for even–even [Formula: see text] isotopes is elucidated showing a negative linear relation. The feasibility of cluster emission from the superheavy isotope [Formula: see text] is investigated using different theoretical approaches. The predictions can provide useful guidance for future experimental researches.

Spectroscopy along flerovium decay chains. II. Fine structure in odd- A Fl289

Fifteen correlated α-decay chains starting from the odd-A superheavy nucleus Fl289 were observed following the fusion-evaporation reaction Ca48+Pu244. The results call for at least two parallel α-decay sequences starting from at least two different states of Fl289. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed α-electron and α-photon coincidences, as well as the α-decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between Cn285 and Ds281. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing ground for theory. This is illustrated by comparison with new nuclear structure calculations based on the symmetry-conserving configuration mixing theory.Received 12 April 2022Revised 1 September 2022Accepted 16 December 2022DOI:https://doi.org/10.1103/PhysRevC.107.L021301Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayLow & intermediate energy heavy-ion reactionsNuclear structure & decaysPropertiesA ≥ 220TechniquesNuclear density functional theoryNuclear Physics

Spectroscopic quadrupole moments in Xe124

Background: The Xe isotopic chain with four valence protons above the Z=50 shell closure is an ideal laboratory for the study of the evolution of nuclear deformation. At the N=82 shell closure, Xe136 presents all characteristics of a doubly closed shell nucleus with a spherical shape. In the very neutron-deficient isotopes close to N=50, the α-decay chain of Xe was investigated to probe the radioactive decay properties near the drip-line and the magicity of Sn100. Additionally, the Xe isotopes present higher order symmetries in the nuclear deformation such as the octupole degree of freedom near N=60 and N=90 or O(6) symmetry in stable isotopes. Purpose: The relevance of the O(6) symmetry has been investigated by measuring the spectroscopic quadrupole moment of the first excited states in Xe124. In the O(6) symmetry limit, the spectroscopic quadrupole moment of collective states is expected to be null. Method: A stable Xe124 beam with energies of 4.03A MeV and 4.11A MeV was used to bombard a natW target at the GANIL facility. Excited states were populated via the safe Coulomb excitation reaction. The collision of the heavy ions with a large Z at low energy make this reaction sensitive to the diagonal E2 matrix element of the excited states. The recoils were detected in the VAMOS++ magnetic spectrometer and the γ rays in the AGATA tracking array. The least squares fitting code gosia was used for the analysis to extract both E2 and M1 transitional and E2 diagonal matrix elements. Results: The rotational ground state band was populated up to the 81+ state as well as the 22+ and 42+ states. Using high precision spectroscopic data to constrain the gosia fit, the spectroscopic quadrupole moments of the 21+, 41+, and 61+ states were determined for the first time. Conclusions: The spectroscopic quadrupole moments were found to be negative, large, and constant in the ground state band underlining the prolate axially deformed ground state band of Xe124. The present experimental data confirm that the O(6) symmetry is substantially broken in Xe124.1 MoreReceived 21 October 2022Accepted 23 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.014324©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsElectromagnetic transitionsSpectroscopic factors & electromagnetic momentsProperties90 ≤ A ≤ 149Nuclear Physics

An improved Gamow-like formula for α-decay half-lives

An improved Gamow-like (IMGL) formula for α-decay half-lives is proposed by introducing an accurate charge radius formula, an analytic expression of assault frequency, the angular momentum taken by α-particle and the isospin effect. The parameters of the IMGL formula are obtained by fitting the experimental α-emitter data with Zp=52–118 (515 α emitters. Zp is the charge number of a parent nucleus) and those with Zp=92–118 (178 α emitters). Correspondingly, the IMGL formula with the parameters fitted the experimental data with Zp=52–118 is named as the IMGL1 formula and the other one is called as the IMGL2 formula. By using the two formulas, a large number of α-decay half-lives are calculated. It is shown that the accuracy of the IMGL1 and IMGL2 formulas is improved significantly compared to their predecessors. Moreover, the accuracy of the IMGL1 and IMGL2 formulas is higher than that of other types of empirical formulas, including the Royer formula, modified Royer (MR) formula, Viola-Seaborg-Sobiczewski (VSS) formula, modified Viola-Seaborg-Sobiczewski (MVSS) formula, formula proposed by Y. Qian and Z. Ren (YQZR) and modified YQZR (MYQZR) formula. In addition, the experimental α-decay half-lives of the synthesized newly neutron-deficient Actinide nuclei and the superheavy nuclei are reproduced well by the two formulas. Then, the α-decay half-lives of the neutron-deficient nuclei with Zp=94-119 are predicted within the IMGL2 formula because its accuracy is higher slightly than that of the IMGL1 formula. Finally, the competition between α-decay and spontaneous fission (SF) with Zp=120 α-decay chains is investigated in detail within the IMGL2 formula and the modified Swiatecki's formula. The predictions of the neutron-deficient nuclei with Zp=94-119 and the superheavy nuclei with Zp=120 are useful for identifying the new nuclides in future experiments.

Macroscopic–microscopic calculations of the ground state properties of Z = 120 isotopes and their α-decay chains

One of the substantial successes achieved in nuclear physics in the last two decades was the synthesis of dozens of isotopes of new elements up to [Formula: see text]Og, which closed the seventh row of the periodic table and inspired the ambition of adding more elements. This work aims to study extensively the ground state structure and decay properties of proposed [Formula: see text] isotopes. We employed Macroscopic–microscopic scheme based on the Skyrme energy density functional, the Woods–Saxon single-particle potential and Strutinsky’s method to find the structure properties, in a multidimensional deformation space. The same nucleon–nucleon potential is used to find the [Formula: see text]-decay half-life, within the Preformed Cluster Model. For 45 [Formula: see text]120 isotopes, the total energy surfaces, ground state masses, binding energy, deformations and fissionability are determined. The [Formula: see text]-values of the different competing decays and [Formula: see text]-decay half-lives are investigated based on the obtained structure. The results indicate the [Formula: see text]120 isotopes to be the most bound among the studied isotopes. The smallest fission barriers are indicated for the [Formula: see text]120 isotopes. The [Formula: see text]120 isotopes showed the longer half-lives against [Formula: see text]-decay, with an order of [Formula: see text]. The longest half-lives are estimated for the [Formula: see text]120 ([Formula: see text] and [Formula: see text]120 ([Formula: see text] isotopes. The longest full decay chain ending with the stable [Formula: see text]Pb nucleus is anticipated for the [Formula: see text]120 isotope. The shortest decay chain of [Formula: see text]120 terminates after three [Formula: see text]-decays by the spontaneous fission of [Formula: see text]Fl.

Theoretical Investigation of α-decay Chains of Fm-isotopes

Background: The theoretical and experimental investigations of decay properties of heavy and superheavy nuclei are crucial to explore the nuclear structure and reaction dynamics.
 Purpose: The aim of this study is to probe the α-decay properties of 243Fm and 245Fm isotopic chains using relativistic mean-field (RMF) approach within the framework of preformed cluster-decay model (PCM).
 Methods: The RMF densities are folded with the relativistic R3Y NN potential to deduce the nuclear interaction potential between the α particle and daughter nucleus. The penetration probability is calculated within the WKB approximation.
 Results: The α-decay half-lives of even-odd 243Fm and 245Fm isotopes and their daughter nuclei are obtained from the preformed cluster-decay model. These theoretically calculated half-lives are found to be in good agreement with the recent experimental measurements.
 Conclusions: The novel result here is the applicability of the scaling factor within the PCM as a signature for shell/sub-shell closures in α-decay studies. As such, we have also demonstrated that N=137, 139 and Z=94 corresponding to 231,233Pu could be shell/sub-shell closures. The least T1/2 is found at 243,245Fm which indicate their individual stability and α-decay as their most probable decay mode.

Improved effective liquid drop model for α-decay half-lives

The effective liquid drop model (ELDM) is improved by introducing an accurate nuclear charge radius formula and an analytic expression of the effective assaulting frequency. Within the improved effective liquid drop model (IMELDM), the α-decay half-lives of 421 nuclei which have been measured in experiment are calculated. It is shown that the accuracy of the IMELDM is improved evidently compared to its predecessor. Meanwhile, by focusing on the superheavy nuclei (SHN), the α-decay half-lives of SHN are investigated within the IMELDM. It is found that the experimental α-decay half-lives of 80 SHN are reproduced well. Then, within the IMELDM the α-decay half-lives of the Z=118–121 isotopes are predicted by inputting the α-decay energies (Qα) extracted from the Weizsäcker-Skyrme-4 (WS4) mass table. At last, the competition between the α-decay and spontaneous fission (SF) of the SHN of the N=178 α-decay chains is studied in detail, which may be useful for searching for the new SHN in future.

A new empirical formula for α-decay half-life and decay chains of Z = 120 isotopes

Experimental α-decay half-life, spin, and parity of 398 nuclei in the range Z are utilized to propose a new formula (QF) with only 4 coefficients as well as to modify the Tagepera-Nurmia formula with just 3 coefficients (MTNF) by employing nonlinear regressions. These formulas, based on reduced mass (μ) and angular momentum taken away by the α-particle, are ascertained very effective for both favoured and unfavoured α-decay in addition to their excellent match with all (Z, N) combinations of experimental α-decay half-lives. After comparing with similar other empirical formulas of α-decay half-life, QF and MTNF formulas are purported with accuracy, minimum uncertainty and deviation, dependency on least number of fitted coefficients together with less sensitivity to the uncertainties of Q-values. The QF formula is applied to predict α-decay half-lives for 724 favoured and 635 unfavoured transitions having experimentally known Q-values. Moreover, these available Q-values are also employed to test various theoretical approaches viz. RMF, FRDM, WS4, RCHB, etc along with machine learning method XGBoost for determining theoretical Q-values, incisively. Thereafter, using Q-values from the most precise theoretical treatment mentioned above along with the proposed formulas, probable α-decay chains for Z = 120 isotopes are identified.

Structural and decay properties of nuclei appearing in the α-decay chains of 296,298,300,302,304120 within the relativistic mean field formalism

An extensive study of [Formula: see text]-decay half-lives for various decay chains of isotopes of [Formula: see text] is performed within the axially deformed relativistic mean-field (RMF) formalism by employing the NL3, NL3[Formula: see text], and DD-ME2 parameter set. The structural properties of the nuclei appearing in the decay chains are explored. The binding energy, quadrupole deformation parameter, root-mean-square charge radius, and pairing energy are calculated for the even–even isotopes of [Formula: see text], which are produced in five different [Formula: see text]-decay chains, namely, [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. A superdeformed prolate ground state is observed for the heavier nuclei, and gradually the deformation decreases towards the lighter nuclei in the considered decay chains. The RMF results are compared with various theoretical predictions and experimental data. The [Formula: see text]-decay energies are calculated for each decay chain. To determine the relative numerical dependency of the half-life for a specific [Formula: see text]-decay energy, the decay half-lives are calculated using four different formulas, namely, Viola–Seaborg, Alex–Brown, Parkhomenko–Sobiczewski and Royer for the above said five [Formula: see text]-decay chain. We notice a firm dependency of the half-life on the [Formula: see text]-decay formula in terms of [Formula: see text]-values for all decay chains. Further, this study also strengthens the prediction for the island of stability in terms of magic number at the superheavy valley in the laboratories.

Prediction of half-lives of even–even superheavy nuclei

α-decay half-lives (-values) of even–even and superheavy nuclei (SHN) are determined employing interaction potential involving Coulomb and proximity potentials. The obtained results are compared with the experimental ones and to assess the precision of the present model in reproducing the experimental half-lives, a comparison is drawn with the other methods as well. We require disintegration energy (Q α -values) as an input in order to predict the (-values) of an experimentally unknown SHN. So, utilizing periodic-orbit theory within microscopic-macroscopic formalism, we have calculated the binding energies and thereafter, Q α -values of known SHN. The results are found to be in good agreement with the experimental ones. Subsequently, we predict the logarithmic values of ’s for even–even unknown SHN whose atomic numbers lie in 118 ⩽ Z ⩽ 126 regime and compare our results with those calculated employing other theoretical methods. Also, the study of spontaneous fission half-lives and branching ratios leads us to predict the SHN which can be identified through α-decay chains in the laboratories. We believe that this work can play a significant role in the experiments leading to the synthesis and identification of new superheavy elements.

Search for α-decay chains for superheavy nuclei with Z=125-127

We have studied the alpha-decay (AD) and spontaneous fission (SF) properties of the isotopes of Z=125, 126 and 127 superheavy nuclei. AD calculations have been performed over all the possible isotopes of Z=125-127 nuclei within the framework of Wentzel-Kramers-Brillouin (WKB) and Bohr-Sommerfeld quantization condition. To broaden the perspective of the calculations, we have also utilized from the analytic formula of Royer in the calculations of AD. In this way we believe that by using various approaches might be useful for the clarity of the predictions. Also, the SF half-lives have been computed by using formulae of Soylu and KPS. Decay modes for the isotopes are determined by using the results of different models. The decay modes obtained for Z=125 and Z=126 have been compared with the results of other studies, and α-decay chains have been presented for Z=127. Findings would provide opportunities for the future experimental researches.

Self-consistent calculations of electron-capture decays in Z=118, 119, and 120 superheavy isotopes

Weak decays in superheavy nuclei with proton numbers Z=118−120 and neutron numbers N=175−184 are studied within a microscopic formalism based on deformed self-consistent Skyrme Hartree-Fock mean-field calculations with pairing correlations. The half-lives of β+ decay and electron capture are compared with α-decay half-lives obtained from phenomenological formulas. The sensitivity of the half-lives to the unknown Q-energies is studied by comparing the results obtained from different approaches for the masses. It is shown that α-decay is always dominant in this mass region. The competition between α and β+/EC decay modes is studied in seven α-decay chains starting at different isotopes of Z=118, 119, and 120.

Spectroscopy along Flerovium Decay Chains: Discovery of ^{280}Ds and an Excited State in ^{282}Cn.

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely ^{282}Cn. Spectroscopy of ^{288}Fl decay chains fixed Q_{α}=10.06(1) MeV. In one case, a Q_{α}=9.46(1)-MeV decay from ^{284}Cn into ^{280}Ds was observed, with ^{280}Ds fissioning after only 518 μs. The impact of these findings, aggregated with existing data on decay chains of ^{286,288}Fl, on the size of an anticipated shell gap at proton number Z=114 is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.

Evaluation for half-lives in α-decay chains of 309−312126 based on semi-empirical approaches

In this paper, we estimated half-lives using semi-empirical formulae for isotopes with Z = 100 − 126 in four α-decay chains, which can appear in the syntheses of the 309−312126 nuclei. The spontaneous fission half-lives were calculated using the Anghel, Karpov, and Xu models, whereas the α-decay ones were predicted using the Viola-Seaborg, Royer, Akrawy, Brown, modified formulae of Royer, Ni, and Qian approaches. We found that there are large differences among the spontaneous fission half-lives estimated using the Xu model and those calculated using the others, which are up to 50 orders of magnitude. The α-decay half-lives also have large uncertainties due to difference in either methods or uncertainties in nuclear mass and spin-parities. Subsequently, there is an argument in determination of α-emitters, especially for the 312126 isotope. On the other hand, the α-decay half-lives are in the range from a few microseconds (309−312126) to thousands of years (257−260Fm) in the decay chains. It was found that the half-lives are very sensitive to not only the shell closure but also the angular momentum in the α decay. For experiments, with relatively long half-lives (a few milliseconds), the 289−292Lv isotopes can be observed as evidences for syntheses of the unknown super-heavy 309−312126 nuclei. Furthermore, measurements for precise mass, fission barrier, and spin-parity are necessary to improve accuracy of half-life predictions for super-heavy nuclei.

Microscopic description of structural, surface, and decay properties of Z=124, 126 superheavy nuclei

A systematic investigation has been carried out for even-even isotopic series of two superheavy nuclei with Z=124 and Z=126 in the region 160≤N≤220, and 162≤N≤218, respectively, within the framework of covariant density functional theory (CDFT). Based on the potential energy curves calculated using the explicit density-dependent meson-exchange (DD-ME) and point-coupling (DD-PC) models, many sensitive observables have been analyzed to understand the structural evolution, shape coexistence, and to predict the possible candidates for neutron shell-closure within the isotopic series of Z=124 and Z=126. The shell correction energy and nuclear symmetry energy have been evaluated within the Strutinsky shell correction approach and the Coherent Density Fluctuation Model (CDFM), respectively. All the sensitive observables i.e. two-neutron separation energy, its differential, neutron-pairing energy, single-particle energy levels, and total shell-correction energy reproduce known spherical neutron magic numbers, and present evidence on new deformed neutron magic numbers at N=168, 174 and 178. The symmetry energy shows a direct correlation with the shape of the system. The α-decay chain of four isotopes 124298,302 and 126300,304 have been studied within three different semi-empirical approaches named UNIV2, SemFIS2 and ImSahu, and compared with the available experimental data, FRDM2012 and the WS4 mass model. All the models, DD-ME2, DD-PC1, FRDM2012, and WS4 have predicted around 8α to 10α decay before spontaneous fission (SF) can start.

Structural properties and α-decay chains of transfermium nuclei (101≤Z≤110)

Transfermium nuclei (101≤Z≤110) are investigated thoroughly to describe structural properties viz. deformation, radii, shapes, magicity, etc. as well as their probable decay chains. These properties are explored using relativistic mean-field (RMF) approach and compared with other theories along with available experimental data. Neutron numbers N=152 and 162 have come forth with a deformed shell gap whereas N=184 is ensured as a spherical magic number. The region with N>168 bears witness of the phenomenon of shape transition and shape coexistence for all the considered isotopic chains. Experimental α-decay half-lives are compared with our theoretical half-lives obtained by using various empirical/semi-empirical formulas. The recent formula proposed by Manjunatha et al., which results best among the considered 10 formulas, is further modified by adding asymmetry dependent terms (I and I2). This modified Manjunatha formula is utilized to predict probable α-decay chains that are found in excellent agreement with available experimental data.