Decay Half-lives Of Superheavy Nuclei Research Articles

Impact of nuclear rotation corrections on alpha decay half-lives of superheavy nuclei within 98 ≤ Z ≤ 120

The influence of nuclear rotation on the decay half-lives of superheavy nuclei within the range 98≤Z≤120 is investigated using the axially deformed relativistic Hartree-Bogoliubov theory in the continuum (DRHBc) with the PC-PK1 parameter set. The deduced DRHBc decay energies (with and without the rotation effect) are compared with those calculated from the macroscopic-microscopic WS4 and the available experimental binding energies. Six semi-empirical formulae, such as the Viola-Seaborg formula (VSS), the modified Brown formula (mB1), the semi-empirical relationship based on fission theory (SemFIS2), the Royer formula (R), the Wang formula (Wang) and the modified YQZR formula (MYQZR) are employed to estimate the half-lives of α decay. Among these formulae, the half-live predictions of SemFIS2 are found to gradually deviate from the systematic trend beyond Nd=184, showing that the probability of undergoing spontaneous fission is less feasible beyond this point. A minimum is observed at Nd=184, reflecting its neutron shell closure for the mass region considered on the nuclear chart. The results further indicate that, for 98≤Z≤104, the predictions of all semi-empirical formulae are more closely matched to the available experimental data when the rotation effect is taken into account. However, we have demonstrated that the effect of nuclear rotation gradually reduces as the atomic nucleus becomes heavier.

Alpha decay half-lives of superheavy nuclei 104 ≤ Z ≤ 125

In order to describe scattering, fusion, fission and ground state masses, Krappe and collaborators developed unified nuclear potential, by generalizing liquid drop model. They have incorporated phenomenological parameters accounting for the attractive force between two separated fragments. One of the phenomenological parameters involved in this model is the range of folded Yukawa function, which accounts for surface diffuseness of the potential and short range attractive interaction. The role of range of folding function of Yukawa-plus-exponential potential is analyzed for alpha decay of heavy and superheavy nuclei. Significant effect of this function is noted in preformation probability which improves the accuracy of half-lives of alpha decay. Half-lives for alpha decay are better obtained for two values of the range of folding function 0.54 and 0.8[Formula: see text]fm for heavy and superheavy mass regions, respectively. The study confirms the associated shell structure [Formula: see text] in heavy nuclei and [Formula: see text] and [Formula: see text] in superheavy nuclei. The calculations are extended to predict the half-lives of superheavy nuclei with [Formula: see text] and [Formula: see text] which are not yet synthesized experimentally.

Predictions for the α decay of superheavy nuclei of Z = 119 − 120 isotopes

A new α preformation factor formula was proposed in the framework of unified fission model (UFM), the coefficients of the formula were obtained by fitting the extracted α preformation factors of 465 nuclei with Z=62−103. The root mean square (RMS) deviation of the calculated α preformation factors with the extracted values is 0.388, indicating that the formula can describe the α particle preformation probability reliably. Then the α decay half-lives for recently observed 76 superheavy nuclei (SHN) are calculated by the UFM with the new α preformation factor formula. The comparison between the calculated values and the experimental data demonstrates that the UFM taking the preformation factor into account is a useful tool to investigate the α decay half-lives of SHN. Encouraged by this, the predictions of α decay half-lives for SHN Z=119,120 isotopes are made by using the theoretical mass tables FRDM2012, WS4 and WS2016+RBFs to determine the Qα values. The predictions can provide references for experiments of synthesizing new SHN if the mass tables are accurate enough.

α -decay properties of even-even superheavy nuclei

In this paper, we have calculated the $\alpha$-decay half-lives of superheavy nuclei with $106 \leq Z \leq 126$ and a neutron number of $150 \leq N \leq 200$ within proximity potentials and deformed-spherical Coulomb potentials by using $WS4$ $\alpha$-decay energy and the semi-classical Wentzel-Kramers-Brillouin approximation for penetration probability. Besides, we have included the preformation factor within the cluster-formation model. We have investigated magic numbers and submagic numbers in the mentioned region; with high probability 162, 178, and 184 are predicted as neutron magic numbers. We also have confirmed that there is good agreement between our predicted half-lives and the ones obtained from semiempirical relationships such as Royer, VSS, UDL, and SemFIS2.

Semi-empirical formula for alpha and cluster decay half-lives of superheavy nuclei

We have formulated a semi-empirical formula for alpha decay half-lives and cluster decay half-lives for superheavy nuclei of atomic number range [Formula: see text]. We have compared the logarithmic half-lives produced by the present formula with that of experiments and other formulae, such as universal decay law (UDL) [H. C. Manjunatha and K. N. Sridhar, Eur. Phys. J. A 53, 156 (2017)] and Horoi et al. [Horoi et al., J. Phys. G[Formula: see text] Nucl. Part. Phys. 30, 945 (2004)], Univ [D. Ni and Z. Ren, Phys. Rev. C 74, 014304 (2006)], Royer [G. Royer, J. Phys. G: Nucl. Part. Phys. 26, 1149 (2000)] and VSS [S. A. Gurvitz and G. Kalbermann, Phys. Rev. Lett. 59, 262 (1987)]. The constructed formula produces logarithmic half-lives for alpha and cluster decay (4He,9Be, [Formula: see text]B, [Formula: see text]C, [Formula: see text]N, [Formula: see text]O, [Formula: see text]F, [Formula: see text]Ne, [Formula: see text]Na, [Formula: see text]Mg, [Formula: see text]Al, [Formula: see text]Si, [Formula: see text]P, [Formula: see text]S, [Formula: see text]Cl, [Formula: see text]Ar, [Formula: see text]K and [Formula: see text]Ca) in superheavy nuclei of atomic number range [Formula: see text].

The predictions on the heavier cluster decays of superheavy nuclei

We have calculated the half-lives of the $ \alpha$ and heavy-cluster decays of superheavy nuclei in the framework of the Wentzel-Kramers-Brillouin (WKB) method. Good agreement with the present experimental data with the WKB method and Universal Decay Law (UDL) has been obtained for the $ \alpha$ -decay half-lives of superheavy nuclei having proton numbers with $ 107 \le Z \le 118$ . We have utilized the cluster preformation factor form proposed by Santhosh and Nithya [#!san!#] with new parameters sets produced by fitting of the results with the UDL formula in order to obtain the cluster decay half-lives. Reasonable results have been obtained by using the cluster preformation factor together with the WKB formalism for the cluster decays. Furthermore, ratio calculations have been performed to find out the candidates of possible cluster emitters. The predictions for cluster emitters are in agreement with estimates with the CPPM model by Santhosh and Nithya [#!san!#] and new additional estimates with the WKB and UDL are made. The present results and predictions would be important for both the theoretical and experimental studies in this field.

α -decay half-lives of superheavy nuclei from a modified generalized liquid-drop model

The \ensuremath{\alpha}-decay half-lives of superheavy nuclei are studied using the generalized liquid-drop model (GLDM) with 1977 nuclear proximity potential proposed by Blocki et al. [Ann. Phys. (NY) 105, 427 (1977)]. The result obtained with the present formalism is compared with the experimental half-lives and half-lives using GLDM. The standard deviation of the present approach is found to be 0.34, which is less than that of GLDM of Royer (0.56). The study is extended to predict the \ensuremath{\alpha} half-lives of some of the unknown isotopes in superheavy region. We hope that the predictions on the \ensuremath{\alpha}-decay half-lives using the present formalism may be helpful in future investigations in this field.

Role of constant value of surface diffuseness in alpha decay half-lives of superheavy nuclei

By using WKB method and considering deformed Woods–Saxon nuclear potential, deformed Coulomb potential, and centrifugal potential, the alpha decay half-lives of 68 superheavy alpha emitters have been calculated. The effect of the constant value of surface diffuseness parameter in the range of 0.1 [Formula: see text]a [Formula: see text] 0.9 (fm) on the potential barrier, tunneling probability, assault frequency, and alpha decay half-lives has been investigated. Significant differences were observed for alpha decay half-lives and decay quantities in this range of surface diffuseness. Good agreement between calculated half-lives with fitted surface diffuseness parameter a = 0.54 (fm) and experiment was observed.

The predictive accuracy of analytical formulas and semiclassical approaches for α decay half-lives of superheavy nuclei

Systematic calculations on the α decay half-lives are performed by using three analytical formulas and two semiclassical approaches. For the three analytical formulas, the experimental α decay half-lives and values of the 66 reference nuclei have been used to obtain the coefficients. We get only four adjustable parameters to describe α decay half-lives for even–even, odd–A, and odd–odd nuclei. By comparison between the calculated values from ten analytical formulas and experimental data, it is shown that the new universal decay law (NUDL) foumula is the most accurate one to reproduce the experimental α decay half-lives of the superheavy nuclei (SHN). Meanwhile it is found that the experimental α decay half-lives of SHN are well reproduced by the Royer formula although many parameters are contained. The results show that the NUDL formula and the generalized liquid drop model (GLDM2) with consideration of the preformation factor can give fairly equivalent results for the superheavy nuclei.

Theoretical approaches to alpha decay half-lives of super-heavy nuclei

We consider the systematics of α-decay half-lives of super-heavy nuclei versus the decay energy and the total α-kinetic energy. We calculate the half-lives using the experimental Qα values. The computed half-lives are compared with the experimental data and with existing empirical estimates and are found to be in good agreement. Also, we obtain α-preformation factors from the ratio between theoretical and experimental results for some super-heavy nuclei and evaluate the standard deviation. The results indicate the acceptability of the approach.

Preformation factor and alpha decay half-lives of superheavy nuclei

The α-decay preformation probabilities of superheavy nuclei are determined within the binary cluster model by using an interaction generated from a combination of a microscopic and a phenomenological interactions. The calculated α-decay half-lives are compared with the experimental data by also taking into consideration, the predicted angular momentum transfer in the decay process.

New approach for alpha decay half-lives of superheavy nuclei and applicability of WKB approximation

The alpha decay half-lives of recently synthesized superheavy nuclei (SHN) are calculated by applying a new approach which estimates them with the help of their neighbors based on some simple formulas. The estimated half-life values are in very good agreement with the experimental ones, indicating the reliability of the experimental observations and measurements to a large extent as well as the predictive power of our approach. The second part of this work is to test the applicability of the Wentzel-Kramers-Brillouin (WKB) approximation for the quantum mechanical tunneling probability. We calculated the accurate barrier penetrability for alpha decay along with proton and cluster radioactivity by numerically solving Schr\"odinger equation. The calculated results are compared with those of the WKB method to find that WKB approximation works well for the three physically analogical decay modes.

Stability againstαdecay of some recently observed superheavy elements

The probability of $\alpha$ particle emission for some recently observed superheavy nuclei (SHN) are investigated. The $\alpha$-decay half lives of SHN are calculated in a quantum tunneling model with density dependent M3Y (DDM3Y) effective nuclear interaction using theoretical and measured $Q_\alpha$ values. We determine the density distribution of $\alpha$ and daughter nuclei from the relativistic mean field theory (RMF) using FSUGold force, NL3 and TM1 parameter sets. The double folded nuclear potential is numerically calculated in a more microscopic manner using these density distributions. The estimated values of $\alpha$-decay half-lives are in good agreement with the recent data. We compare our results with recently detected $\alpha$-decay chains from new element with atomic number Z=117 reported by JINR, Dubna. Finally, we determine the half-lives of superheavy elements with Z=108-120 and neutron number N=152-190 to explore the long-standing predictions on the existence of an "island of stability" due to possible spherical proton (Z$\sim 114$) and neutron (N$\sim 184$) shell closures.

Search for long lived heaviest nuclei beyond the valley of stability

The existence of long lived superheavy nuclei (SHN) is controlled mainly by spontaneous fission and \ensuremath{\alpha}-decay processes. According to microscopic nuclear theory, spherical shell effects at $Z=114$, 120, 126 and $N=184$ provide the extra stability to such SHN to have long enough lifetime to be observed. To investigate whether the so-called ``stability island'' could really exist around the above $Z$, $N$ values, the \ensuremath{\alpha}-decay half-lives along with the spontaneous fission and \ensuremath{\beta}-decay half-lives of such nuclei are studied. The \ensuremath{\alpha}-decay half-lives of SHN with $Z=102$--120 are calculated in a quantum tunneling model with DDM3Y effective nuclear interaction using ${Q}_{\ensuremath{\alpha}}$ values from three different mass formulas prescribed by Koura-Uno-Tachibana-Yamada (KUTY), Myers-Swiatecki (MS), and Muntian-Hofmann-Patyk-Sobiczewski (MMM). Calculation of spontaneous fission (SF) half-lives for the same SHN are carried out using a phenomenological formula and compared with SF half-lives predicted by Smolanczuk et al. A possible source of discrepancy between the calculated \ensuremath{\alpha}-decay half-lives of some nuclei and the experimental data of GSI, JINR-FLNR, RIKEN, is discussed. In the region of $Z=106$--108 with $N~$ 160--164, the \ensuremath{\beta}-stable SHN ${}_{106}^{268}{\text{Sg}}_{162}$ is predicted to have highest \ensuremath{\alpha}-decay half-life (${T}_{\ensuremath{\alpha}}~3.2$ h) using ${Q}_{\ensuremath{\alpha}}$ value from MMM. Interestingly, it is much greater than the recently measured ${T}_{\ensuremath{\alpha}}$ ($~22$ s) of deformed doubly magic ${}_{108}^{270}{\text{Hs}}_{162}$ nucleus. A few fission-survived long-lived SHN which are either \ensuremath{\beta}-stable or having large \ensuremath{\beta}-decay half-lives are predicted to exist near ${}^{294}{110}_{184}$, ${}^{293}{110}_{183}$, ${}^{296}{112}_{184}$, and ${}^{298}{114}_{184}$. These nuclei might decay predominantly through \ensuremath{\alpha}-particle emission.

α-nucleus potentials, α-decay half-lives, and shell closures for superheavy nuclei

Systematic \ensuremath{\alpha}-nucleus folding potentials are used to analyze \ensuremath{\alpha}-decay half-lives of superheavy nuclei. Preformation factors of about several percent are found for all nuclei under study. The systematic behavior of the preformation factors and the volume integrals of the potentials allows predictions of \ensuremath{\alpha}-decay energies and half-lives for unknown nuclei. Shell closures can be determined from measured \ensuremath{\alpha}-decay energies using the discontinuity of the volume integral at shell closures. For the first time a double shell closure is predicted for ${Z}_{\mathrm{magic}}=132,{N}_{\mathrm{magic}}=194$, and ${A}_{\mathrm{magic}}=326$ from the systematics of folding potentials. The calculated \ensuremath{\alpha}-decay half-lives remain far below 1 ns for superheavy nuclei with double shell closure and masses $Ag300$ independent of the precise knowledge of the magic proton and neutron numbers.

PROPERTIES OF SUPERHEAVY NUCLEI IN VARIOUS MACROSCOPIC-MICROSCOPIC MODELS

In the framework of various macroscopic-microscopic models we examine the ground state properties: separation energies, mean square charge radii, electric quadrupole moments as well as fission barriers, mass parameters, spontaneous fission and α decay half-lives of superheavy nuclei. Four macroscopic models and two models of pairing interactions are applied and studied. The approach is based on the deformed Woods-Saxon potential. Spontaneous fission half-lives are calculated within a multi-dimensional dynamical-programming method where the action integral is minimized within the three dimensional space of the nuclear deformation parameters {β2, β4, β6}.