Superheavy Isotopes Research Articles

α Decay Properties of Even-Even Nuclei296–308120 Within the Two-Potential Approach**Supported by National Natural Science Foundation of China under Grant Nos. 11205083 and 11505100, the construct program of the key discipline in Hunan province, the Research Foundation of Education Bureau of Hunan Province, China under Grant Nos. 15A159 and 18A237, the Natural Science Foundation of Hunan Province, China under Grant Nos.

In the present work, we predict the α decay half-lives of unknown even-even nuclei296–308120 within the two-potential approach, whose α decay energy Qα is calculated using WS3+ mass model. To reduce the deviations between the predictions and experimental data due to nuclear shell effect, the analytic formula of α decay hindrance factor is introduced to the two-potential approach, whose parameters had been extracted from even-even nuclei in the region of 82 < Z ≤ 126 and 152 < N ≤ 184 in our previous work [Deng et al., Chin. Phys. C 42 (2018) 044102]. In addition, for comparing, we use a type of α decay general formula Universal Decay Law (UDL) and a semi-empirical formula in the superheavy nucleus (SEMFLS) to calculate the half-lives of even-even nuclei296–308120. The results indicate that our predicted values and the calculated values of the above two empirical formulas are mutually confirmed. Meanwhile, we systematically study α decay chains of296–308120 and predict the decay modes for superheavy nuclei to help to identify new superheavy isotopes.

Fission analysis of Z = 114 superheavy isotopes formed via heavy-ion induced reactions

The quasi-fission and fission mass distributions for 48Ti + 238U → 286Fl* and 48Ca + 244Pu → 292Fl* reactions are investigated within dynamical cluster decay model by addressing the experimentally available symmetric fission (A/2 ± 20) and asymmetric quasi-fission cross-sections in nuclear deformation space. The contribution of quasi-fission components comes out to be negligibly small for spherical constitution of fragments, which increases significantly on adding deformation effects with the appearance of some sharp peaks in the neighborhood of Z = 82 magicity. The contribution of quasi-fission events increases with increase in isotopic mass of superheavy system with Z = 114.

Inner-shell ionization duringαdecay of superheavy isotopes from the tennessineTs117293and oganessonOg118294chains

Presented here are calculations of probabilities of the $K$-, $L$-, and $M$-shell ionization during $\ensuremath{\alpha}$ decay of superheavy isotopes $_{117}^{293}\mathrm{Ts}$, $_{115}^{289}\mathrm{Mc}$, and $_{113}^{285}\mathrm{Nh}$ involved in the tennessine decay chain as well as $_{118}^{294}\mathrm{Og}$, $_{116}^{290}\mathrm{Lv}$, and $_{114}^{286}\mathrm{Fl}$ involved in the new oganesson decay chain. The ionization probabilities are of importance for handling data obtained by methods of the combined $\ensuremath{\alpha}$, $\ensuremath{\gamma}$, and conversion-electron spectroscopy used in the superheavy element synthesis analysis. Relativistic calculations are based on the quantum mechanical model. Electron wave functions are determined by the Dirac-Fock method. The $\ensuremath{\alpha}$-particle tunneling through the atomic Coulomb barrier is taken into account. Peculiarities of the $K$-, $L$-, and $M$-shell ionization are considered. Results demonstrate that the effect of tunneling through the Coulomb barrier for the $L$ and $M$ shells is of no significance as distinct from the $K$ shell, where the inclusion of the tunneling leads to a considerable decrease of the ionization probability. The probability of ionization from higher shells is larger than that from inner shells. However, the change from the $K$ shell to $L$ shell is much more significant than the change from the $L$ shell to $M$ shell. It has been found that only monopole and dipole terms of the radiative field $L=0,1$ make a contribution to the $K$- and ${L}_{1}$-shell ionization probabilities while contributions of all multipoles $L\ensuremath{\le}4$ may be important for the ${L}_{2}$, ${L}_{3}$, and particularly for ${M}_{1}\ensuremath{-}{M}_{5}$ subshells.

Isotopic yield and half-life of spontaneous fission for Cn284 and Fl284 superheavy isobars using direct calculation and semiempirical formulas

Isotopic yields and half-lives of $^{284}\mathrm{Cn}$ and $^{284}\mathrm{Fl}$ superheavy nuclei are calculated using nuclear proximity and Coulomb potentials. The energy released in fission, $Q$ value, driving potential $(V\ensuremath{-}Q)$, the penetrability through barrier, fission decay constant, and relative yield for each possible pair of fission fragments are obtained. According to the fragments mass and charge asymmetry, the most favored binary fragmentation is occurred for the highest $Q$ value and the lowest driving potential. For spontaneous binary fission of $^{284}\mathrm{Cn}$ superheavy nuclei, the higher relative yields are belong to production of $^{128}\mathrm{Sn}$ and $^{134}\mathrm{Te}$ fragments and for $^{284}\mathrm{Fl}$ superheavy isotope, the maximum yield were observed for $^{136}\mathrm{Xe}$ as one of the fission fragments. The comparison between the obtained isotopic relative yield shows the role of magic and near-magic closed-shell fragments in having the highest isotopic yield. Fission decay constant for each possible fragmentation is calculated and then by summation over them, the total decay constant and fission half-life for $^{284}\mathrm{Cn}$ and $^{284}\mathrm{Fl}$ superheavy nuclei are estimated. Finally, the calculated half-lives using direct method are compared with the results of semiempirical formulas as well as experimental data. Satisfactory agreement is achieved between the results of this approach and the experimental data than the results of semiempirical formulas.

Nuclear level density and thermal properties of 270110, 278112, and 290116 superheavy isotopes in low excitation energies

The level density parameter α is calculated using the semiclassical approach for 270 110, 278 112, and 290 116 superheavy isotopes. The Woods-Saxon potential is considered for the interaction of nucleons inside a nucleus. Thermal properties of these isotopes, including the entropy, the nuclear temperature, and the heat capacity are calculated within the framework of microcanonical ensemble and the back-shifted Fermi gas model with one adjustable parameter E 1 . The process of breaking the first Cooper pair and cooling of the 270 110, 278 112, and 290 116 superheavy isotopes have also been observed.

Alpha-gamma decay studies of 258Db and its (grand)daughter nuclei 254Lr and 250Md

The superheavy isotope 258Db was produced in the 209Bi(50Ti, 1n)258Db reaction at GSI, Germany. A detailed $ \alpha$-spectroscopy study of this isotope and its $ \alpha$-decay daughter products was performed. Two long-lived $ \alpha$-decaying states in 258Db are observed. A spin-parity of $ 0^{-}$ is tentatively assigned to the ground state for which a half-life of $ 2.17 \pm 0.36$ s is determined. Spins and parities of either $ 5^{+}$ or $ 10^{-}$ are proposed for the isomeric state found at an excitation energy of 51 keV with a half-life of $ 4.41 \pm 0.21$ s. The $ \alpha$ -decay daughter isotope 254Lr displays a similar behavior. A half-life of $ 11.9 \pm 0.9$ s is determined for the 254Lr ground state which is tentatively assigned a spin-parity of $ 4^{+}$. The isomeric level of this isotope placed at 108 keV with a half-life of $ 20.3 \pm 4.2$ s is tentatively assigned a spin-parity of $ 1^{-}$. Two long-lived $ \alpha$-decaying states are observed in the granddaughter isotope 250Md . The ground state has a half-life of $ 59.5 \pm 9.1$ s. A half-life of $ 42.4 \pm 4.5$ s is measured for the isomeric state positioned at an excitation energy of 123 keV. Partial, tentative level schemes for 254Lr, 250Md and 246Es are proposed based on the $ \alpha$-$ \gamma$ coincidences.

Saturated-configuration-interaction calculations for five-valent Ta and Db

Accurate atomic structure calculations of complicated atoms with 4 or more valence electrons begin to push the memory and time limits of supercomputers. This paper presents a robust method of decreasing the size of \textit{ab initio} configuration interaction and many-body perturbation theory calculations without undermining the accuracy of the resulting atomic spectra. Our method makes it possible to saturate the CI matrix in atoms with many valence electrons. We test our method on the five-valence-electron atom tantalum and verify the convergence of the calculated energies. We then apply the method to calculate spectra and isotope shifts of tantalum's superheavy analogue dubnium. Isotope-shift calculations can be used to predict the spectra of superheavy isotopes which may be produced in astrophysical phenomena.

Isotopic yield and half-lives for the spontaneous fission of 280Ds and 282Cn, superheavy nuclei

The spontaneous fission of the 280Ds and 282Cn superheavy nuclei has been studied using the isotopic yield method. The Coulomb and the nuclear proximity potentials are considered for the fission barrier. The energy released in fission (Q-values), the driving potential ( $ V-Q$ ), the penetrability, the decay constant and the fission yield for each fragmentation have been calculated. As expected, with respect to the mass and charge asymmetry, the most favorable fragmentation in the binary spontaneous fission occurs for the highest Q-value and consequently for the lowest value of the driving potential. For the spontaneous fission of 280Ds and 282Cn superheavy isotopes, the highest yields have been seen for 134Te $ (N = 82, Z = 52)$ and 136Xe $ (N = 82, Z = 54)$ closed shell magic isotopes, respectively. The role of magic and near magic closed shell fragmentation is indicated by the analysis of the relative yields. The spontaneous fission half-lives of 280Ds and 282Cn have also been obtained and compared with the results of other theoretical and semi-empirical methods as well as experimental data. The comparison has revealed that the results of the present study acceptably agreed with the experimental data than the other theoretical and semi-empirical methods.

Fusion-Barrier Distributions Will Unveil Most Probable Reaction Energies to Synthesize Isotopes of Superheavy Elements Beyond Z = 118

To investigate the correlations between barrier distributions and excitation functions of neutron-evaporation channels (xn channels) in nuclear reactions, researchers have measured fusion-barrier distributions in reaction systems in which superheavy isotopes are synthesized. They found that the excitation functions of 3n and 4n channels in the system 48Ca+248Cm are strongly affected by the deformation of the target nucleus. This finding will enhance our ability to quantitatively predict the most probable reaction energies for further searches of superheavy elements.

He4 , Be10 , C14 , and O16 light-fragment-accompanied cold ternary fission of the Cm250 isotope in an equatorial three-cluster model

The cold ternary fission of $^{250}\mathrm{Cm}$ accompanied with $^{4}\mathrm{He}$, $^{10}\mathrm{Be}$, $^{14}\mathrm{C}$, and $^{16}\mathrm{O}$ light charged particles in the equatorial three-cluster model configuration is studied. Driving potential and fission yield for each accompanied light charged particles for individual fragmentation are calculated. The obtained results reveal that even-mass-number components are more favored than odd-mass-number components. Furthermore, upon increasing the mass of light fixed fragment in ternary fission, the probability of crossing over the potential barrier (driving potential) is decreased considerably due to the height of the potential barrier. The comparison between relative yields for a variety of fragmentation in each group indicates that the presence of doubly or near doubly magic closed-shell fragments are more favored in the cold ternary fission of the $^{250}\mathrm{Cm}$ superheavy isotope.

Shell closures in Fl superheavy isotopes via determination of alpha decay preformation factor

Based on the hypothesized cluster-formation model (CFM), the α-decay preformation factors of superheavy isotopes of Flerovium (Fl) with atomic number Z = 114 and neutron numbers 150 ≤ N ≤ 196 were determined. The formula from the CFM used depends on the eigenvalues of the cluster-formation energy of the α particles and the total energy values of the parent nuclei. The binding energy difference was used to determine these values. The results from the calculations for these isotopes reflect some properties of their nuclear structure. Within the CFM, the prediction of the magic nucleus occurs at N = 172 and Z = 114. Our results indicate towards the existence of shell closure of the stabilization superheavy nuclei.

Predictions of probable projectile-target combinations for the synthesis of superheavy isotopes of Ts

Taking the Coulomb and proximity potential as the interaction barrier, we have studied the production cross section of probable projectile-target combinations for the synthesis of superheavy element $^{297}\mathrm{Ts}$. The cold reaction valley of $^{297}\mathrm{Ts}$ is studied to identify the possible projectile-target combinations for the synthesis of $^{297}\mathrm{Ts}$. The entrance channel Coulomb barrier, the quasifission barrier, and barrier positions for all these combinations are calculated. The fusion probability and survival probability of the excited compound nucleus are evaluated. At energies near and above the Coulomb barrier, the excitation function [capture, fusion, and evaporation residue (ER) cross sections] of these combinations leading to superheavy element (SHE) $^{297}\mathrm{Ts}$ is investigated. It is found that the production cross sections of $^{297}\mathrm{Ts}$ in cold fusion reactions are very small compared to hot fusion reactions. The combinations $^{40}\mathrm{S}+^{257}\mathrm{Md}, ^{42}\mathrm{S}+^{255}\mathrm{Md}, ^{43}\mathrm{Cl}+^{254}\mathrm{Fm}, ^{44}\mathrm{Ar}+^{253}\mathrm{Es}, ^{46}\mathrm{Ar}+^{251}\mathrm{Es}, ^{48}\mathrm{Ca}+^{249}\mathrm{Bk}, ^{50}\mathrm{Ca}+^{247}\mathrm{Bk}, ^{67}\mathrm{Co}+^{230}\mathrm{Th}, ^{68}\mathrm{Ni}+^{229}\mathrm{Ac}, ^{70}\mathrm{Ni}+^{227}\mathrm{Ac}$, and $^{72}\mathrm{Ni}+^{225}\mathrm{Ac}$ are observed to be the most favorable projectile-target pairs for the production of SHE $^{297}\mathrm{Ts}$. Our calculated results are compared with experimental data and with other theoretical studies for the reaction $^{48}\mathrm{Ca}+^{249}\mathrm{Bk}$ leading to $^{297}\mathrm{Ts}$, and are in good agreement with experimental observation of Oganessian et al. Furthermore, the ER cross section for the synthesis of isotopes $^{291\ensuremath{-}296}\mathrm{Ts}$ and $^{298\ensuremath{-}299}\mathrm{Ts}$ using $^{48}\mathrm{Ca}$ induced reactions are studied. Among these isotopes, the isotope $^{298}\mathrm{Ts}$ has larger cross section in the 3n channel using the reaction $^{48}\mathrm{Ca}+^{250}\mathrm{Bk}$, and $^{299}\mathrm{Ts}$ has larger cross section in the 4n channel using the reaction $^{48}\mathrm{Ca}+^{251}\mathrm{Bk}$. Therefore, our theoretical predictions to produce isotopes of the element Ts will be helpful for future experiments, as the isotopes have not been synthesized so far.

Predictions on the modes of decay of even [formula omitted] superheavy isotopes within the range [formula omitted

The decay modes and half lives of all the even Z isotopes of superheavy elements within the range 104≤Z≤136 have been predicted by comparing the alpha decay half-lives with the spontaneous fission half-lives. The Coulomb and proximity potential model for deformed nuclei (CPPMDN) and the shell-effect-dependent formula of Santhosh et al. are used to calculate the alpha half-lives and spontaneous fission half-lives respectively. For theoretical comparison the alpha decay half-lives are also calculated using Coulomb and proximity potential model (CPPM), the Viola–Seaborg–Sobiczewski semi-empirical (VSS) relation, the universal (UNIV) curve of Poenaru et al., the analytical formula of Royer and the universal decay law (UDL) of Qi et al. Another tool used for the evaluation of spontaneous fission half-lives is the semi-empirical formula of Xu et al. The nuclei with alpha decay half-lives less than spontaneous fission half-lives will survive fission and hence decay through alpha emission. The predicted half lives and decay modes are compared with the available experimental results. The one-proton and two-proton separation energies of all the isotopes are calculated to find nuclei which lie beyond the proton drip line. Among 1119 even Z nuclei within the range 104≤Z≤136, 164 nuclei show sequential alpha emission followed by subsequent spontaneous fission. Since the isotopes decay through alpha decay chain and the half-lives are in measurable range, these isotopes are predicted to be synthesized and detected in laboratory via alpha decay. 2 nuclei will decay by alpha decay followed by proton emission, 54 nuclei show full alpha chains, 642 nuclei will decay through spontaneous fission, 166 nuclei exhibit proton decay and 91 isotopes are found to be stable against alpha decay. All the isotopes are tabulated according to their decay modes. The study is intended to enhance further experimental investigations in superheavy region.

Calculations of alpha cluster preformation probability for the three even–even superheavy isotopes with atomic number Z = 108,110 and 112

The accurate calculations of the cluster formation model (CFM) have been extended to determine the alpha cluster preformation probability for the three even–even superheavy isotopes (Hs, Ds and Cn) with atomic number [Formula: see text] and 112 and neutron numbers [Formula: see text] in the mass region from 252 to 300. According to the hypothesized CFM, the calculations of the formation energy and surface energy, which depended on differences of binding energies are crucial for determining the realistic values of the preformation probability. Our results showed reasonable agreement with the results of previous work for the heavy nuclei. In addition, realistic values of the preformation probability certified that CFM can successfully be used to calculate the alpha cluster preformation probability for other wide range of superheavy nuclei.

Decay of heavy particles from Z = 125 superheavy nuclei in the region A = 295–325 using different versions of proximity potential

Within the framework of Coulomb and proximity potential model (CPPM), the probable heavy particle decays from various isotopes of superheavy nuclei (SHN), [Formula: see text], within the range [Formula: see text]–[Formula: see text] have been studied using two versions of proximity potential; proximity 1977 and proximity 2000. The decay half lives evaluated using proximity 2000 is observed to be higher than the values obtained using proximity 1977. The effect of surface deformation on the decay half lives is studied using Coulomb and proximity potential for deformed nuclei (CPPMDN). As a result of the inclusion of deformation [Formula: see text], the penetrability of the decays are observed to be increased and accordingly the decay half lives are reduced. The estimated values are compared with other theoretical models, Universal curve (UNIV), Universal Decay law (UDL) and the scaling law of Horoi. The odd–even staggering (OES) effect is observed in the emission of odd mass clusters. An intriguing aspect of the study is the effect of the magicity at [Formula: see text] which is confirmed from the plot of [Formula: see text] against the neutron number of the daughter nuclei. Almost all the predicted half lives are favorable for experimental measurements. The Geiger–Nuttall (GN) plots and the Universal curve have been studied for various cluster emissions from various superheavy isotopes with [Formula: see text]. Finally, the linearity of the GN plot and the Universal curve of the heavy particle emissions very well established the strength of CPPM.

Ways to produce new superheavy isotopes with Z = 111–117 in charged particle evaporation channels

Abstract The excitation functions of the production of new heaviest isotopes of superheavy nuclei with charge numbers 111–117 in the pxn and αxn evaporation channels of the 48Ca-induced hot fusion reactions are predicted for the first time for future experiments.

Search for light neutron-rich isotopes in stopped pion absorption

The results based on the spectroscopy of superheavy hydrogen isotopes (4−7H), heavy helium isotopes (6,7He), and heavy lithium isotopes (7−12Li) produced in stopped pion absorption by light nuclei were analyzed. Search for nuclear states was performed in inclusive and correlation measurements of missing mass spectra. A broad range of excitation energies studied in correlation measurements provided the possibility of search for isobaric analog states and cluster resonances. A comparison with experimental and theoretical results of other authors was conducted.

Feasibility of observing the α decay chains from isotopes of SHN with Z = 128, Z = 126, Z = 124 and Z = 122

Within the Coulomb and proximity potential model for deformed nuclei (CPPMDN), the alpha decay properties of 34 isotopes of the superheavy nuclei with Z=128 within the range 306≤A≤339 have been studied, considering both the parent and daughter nuclei to be deformed. The manuscript also deals with the decay properties of the isotopes of Z=126 (within 288≤A≤339), Z=124 (within 284≤A≤339) and Z=122 (within 280≤A≤339). The alpha decay half lives thus evaluated have been compared with the values evaluated using other theoretical models and it was seen that, our theoretical alpha decay half lives match well with these values. Through the present study, we have underlined and have established the fact that, among the 192 isotopes considered in the present study, only those isotopes 321–324,328–335128, 318–320,323–327126, 305–308,315–322124 and 298–307,311–314122 can be synthesised and detected through alpha decay in laboratory. As the alpha decay half lives of these superheavy isotopes lie within the experimental limits, we hope these predictions, on the decay modes of these unknown nuclei, to pave the way for the future experiments. The proton separation energy calculations on 306–339128, 288–336126, 284–339124 and 280–339122 superheavy nuclei have also been done and the study revealed the probable proton emitters among these nuclei.

Alpha Decay Preformation Factors for Even–Even 280–316116 Superheavy Isotopes

The success of the cluster formation model (CFM) in deriving an energy-dependent formula for the preformation factors of heavy nuclei has motivated us to expand this approach to the superheavy isotopes (SHI). In this paper, the alpha-cluster formation (preformation factor) behavior inside the parent nuclei of SHI with atomic number Z = 116 and neutron numbers 164 ≤ N ≤ 200 is determined using the alpha preformation formula contained within the CFM. The cluster formation energy of the alpha particles and the total energy of the parent nuclei are calculated on the basis of the various binding energies. Our results clearly show that the CFM remains valid for superheavy nuclei (SHN). In addition, our calculations reveal that the alpha clustering mechanism and formation probability in 280–316116 even–even SHI are similar to those of even–even heavy nuclei in a general sense.

Candidates for long-lived high-Kground states in superheavy nuclei

On the basis of systematic calculations for 1364 heavy and superheavy nuclei, including odd-systems, we have found a few candidates for high-K ground states in superheavy nuclei. The macroscopic-microscopic model based on the deformed Woods-Saxon single particle potential which we use offers a reasonable description of SH systems, including known: nuclear masses, $Q_{\alpha}$-values, fission barriers, ground state deformations, super- and hyper-deformed minima in the heaviest nuclei. %For odd and odd-odd systems, both ways of including pairing correlations, % blocking and the quasi-particle method, have been applied. Exceptionally untypical high-K intruder contents of the g.s. found for some nuclei accompanied by a sizable excitation of the parent configuration in daughter suggest a dramatic hindrance of the $\alpha$-decay. Multidimensional hyper-cube configuration - constrained calculations of the Potential Energy Surfaces (PES's) for one especially promising candidate, $^{272}$ Mt, shows a $\backsimeq$ 6 MeV increase in the fission barrier above the configuration- unconstrained barrier. There is a possibility, that one such high-K ground- or low-lying state may be the longest lived superheavy isotope.