An improved α-decay energy formula for heavy and superheavy nuclei

Based on the liquid-drop model and using the first derivative of the normalized Gaussian function to consider the shell correction,a simpleα-decay energy formula is proposed for heavy and superheavy nuclei.The values of corresponding adjustable parameters are obtained by fittingα-decay energies of 209 nuclei ranging from Z=90 to Z=118 with N≥140.The calculated results are in good agreement with the experimental data.The average and standard deviations between the experimental data and theoretical results are 0.141 and 0.190 Me V,respectively.For comparison,the reliable formulae proposed by Dong T K et al(2010,Phys.Rev.C 82,034320),Dong J M et al(2010,Phys.Rev.C 81,064309)and the WS3+nuclear mass model proposed by Wang N et al(2011,Phys.Rev.C 84,051303)are also used.The results indicate that our improved 7-parameter formula is superior to these empirical formulae and is largely consistent with the WS3+nuclear mass model.In addition,we extend this formula to predict theα-decay energies for nuclei with Z=117,118,119 and 120.The predicted results of these formulae are basically consistent.

Global α-decay study based on the mass table of the relativistic continuum Hartree-Bogoliubov theory

The α-decay energies （Qα） are systematically investigated with the nuclear masses for 10 ≤Z ≤120 isotopes obtained by the relativistic continuum Hartree-Bogoliubov （RCHB） theory with the covariant density func- tional PC-PK1, and compared with available experimental values. It is found that the α-decay energies deduced from the RCHB results present a similar pattern to those from available experiments. Owing to the large predicted Qα values （≥4 MeV）, many undiscovered heavy nuclei in the proton-rich side and super-heavy nuclei may have large possibilities for α-decay. The influence of nuclear shell structure on α-decay energies is also analysed.

Determination of isospin asymmetry effects on α-decay

In this study,we compared the effect of the isospin asymmetry of proton and neutron density distributions in the neutron skin-type(NST)case and in the Hartree-Fock formalism(HF)on the half-life of alpha emitters with the atomic number in the range of 82≤Z≤92.The NST case and HF formalism based on the Skyrme-SLy4 effective interaction reveal different isospin asymmetries for selected alpha emitters.Furthermore,the obtained results reveal an increase in theα-decay widths of about 30%for the NST case in comparison with the equivalent values obtained by HF formalism.The standard deviations for calculated half-lives within the NST case and HF formalism are about 0.438 and 0.391,respectively.

α-decay half-lives of superheavy nuclei and general predictions

The generalized liquid drop model （GLDM） and the cluster model have been employed to calculate the α-decay half-lives of superheavy nuclei （SHN） using the experimental α-decay Q values. The results of the cluster model are slightly poorer than those from the GLDM if experimental Q values are used. The prediction powers of these two models with theoretical Q values from Audi et al. （QAudi） and Muntian et al. （QM） have been tested to find that the cluster model with QAudi and QM could provide reliable results for Z 〉 112 but the GLDM with QAudi for Z 112. The half-lives of some still unknown nuclei are predicted by these two models and these results may be useful for future experimental assignment and identification.

Calculations of theα-decay properties of Z=120,122,124,126 isotopes

Theα-decay properties of even-Z nuclei with Z=120,122,124,126 are predicted.We employ the generalized liquid drop model(GLDM),Royer's formula,and universal decay law(UDL)to calculate theα-decay half-lives.By comparing the theoretical calculations with the experimental data of known nuclei from Fl to Og,we confirm that all the employed methods can reproduce theα-decay half-lives well.The preformation factor Pαandα-decay energy Qαshow that ^298,304,314,316,324,326,338,348120,^304,306,318,324,328,338122,and ^328,332,340,344124 might be stable.Theα-decay half-lives show a peak at Z=120,N=184,and the peak vanishes when Z=122,124,126.Based on detailed analysis of the competition betweenα-decay and spontaneous fission,we predict that nuclei nearby N=184 undergoα-decay.The decay modes of ^287−339120,^294−339122,^300−339124,and ^306−339126 are also presented.

INFRARED SPECTRA EFFECT OF α-DECAY DAMAGE IN ZIRCON STRUCTURE

The damage in zircon structure is caused by α-decay which is associated with radiation of uranium and thorium in zircon. Over the narrow dose range from 0.3×1016 to 0.8×1016 α-events mg-1, natural crystalline zircon begins to convert to metamict state. When α-decay dose reaches 0.8×1016 α-events mg-1, the crystalline zircon would be changed to completely metamict state through several million geological years, and the metamict state zircon ap-

Research onα-decay for the superheavy nuclei with Z=118-120

The generalized liquid-drop model(GLDM)with the microscopic shell correction from relativistic Hartree-Fock(RHF)calculations is used to explore theα-decay of superheavy nuclei.The known nuclei with Z=106−118 are chosen as examples for testing.The calculated half-lives ofα-decay agree with the experimental data better than those from the GLDM with the shell correction in the Weizsa¨cker-Skyrme model.Moreover,the influence of the decay energy Q_(α) onα-decay is investigated.It is determined that the Q_(α) values obtained from the WS4 model with radial basis function(RBF)correction match the experimental data optimally.Owing to these advantages,the GLDM with the RHF shell correction and WS4+RBF Q_(α) values is adopted to predict theα-decay lifetime for the unknown superheavy nuclei with Z=118−120.The trend of the availableα-decay half-lives according to the neutron number is similar to the trends of the values from the GLDM calculation without shell correction as well as the universal decay law(UDL)formula.Comparably,the RHF shell correction depresses(raises)theα-decay lifetime for most nuclei with N<186(N>186).In comparison with the half-lives of spontaneous fission,it can be concluded that theα-decay is dominant in the superheavy nuclei ^(281−304)118,^(284−306)119,and ^(287−308)120.These results are beneficial to the exploration of superheavy nuclei in experiments.

α-decay Branching Ratios to Rotational Band of Heavy Even-even and Odd-A Nuclei

By using a simple barrier penetration approach,we predict the α-decay branching ratios to members of ground-state rotational band of heavy even-even No isotopes. We also extend our approach to calculate the α-decay branching ratios to the rotational band of heavy odd-A nuclei. The theoretical branching ratios of α-decays are found in good agreement with the available experimental data.

Evaluation of Natural Radioactivity Levels for Structural Material Used in the Construction of the Neutrino Detector

In this work, the evaluation of natural radioactivity and spontaneous fission rates was performed for 8 nuclides from the natural radioactive 238U, 235U and 232Th decay chains. For this purpose, three samples of structural materials of the neutrino detector, i.e. aluminum, titanium and glass were analyzed by gamma spectroscopy and by neutron activation analysis to quantify a specific radioactivity of the samples. According to the results of this investigation, glass and aluminum samples have maximum values of the mean uranium concentrations 7.3(7) × 10-4% and 3.1(6) × 10-5%, respectively, while the lowest value for mean concentration of the uranium was found in titanium samples to be 4.7(3) × 10-6%. Aluminum sample had maximum values of the mean thorium concentrations, 2.5(8) × 10-3%, while the lowest value for mean concentration of the thorium was found in titanium samples to be 6.2(3) × 10-7%.

Alpha Decay of the Neutron-deficient Isotopes 215,216U

The most neutron-deficient isotopes215,216 U were produced in the complete-fusion reaction ^(180)W(^(40)Ar, 4-5n)^(215,216) U. Evaporation residues recoiled from the target were separated in-flight from the primary beam by the gas-filled recoil separator SHANS and subsequently identified on the basis of correlated α-decay chains. Two α-decaying states were identified in ^(216)U, one for the ground state and the other for the isomeric state with 8+(πh_(9/2)πf_(7/2)) configuration. The α-decay properties for ^(215,216)U and the systematics of 8+isomeric state in N = 124, 126 isotones were investigated.

Constraints on neutron skin thickness and symmetry energy of 208Pb through Skyrme forces and cluster model

We used the cluster structure properties of the 212Po to estimate the neutron skin thickness of 208Pb.For this purpose,we considered two important components:(a)alpha decay is a low energy phenomenon;therefore,one can expect that the mean-field,which can explain the ground state properties of 212Po,does not change during the alpha decay process.(b)212Po has a high alpha cluster-like structure,two protons and two neutrons outside its core nucleus with a double magic closed-shell,and the cluster model is a powerful formalism for the estimation of alpha decay preformation factor of such nuclei.The slope of the symmetry energy of 208Pb is estimated to be 75±25 MeV within the selected same mean-fields and Skyrme forces,which can simultaneously satisfy the ground-state properties of parent and daughter nuclei,as their neutron skin thicknesses are consistent with experimental data.

Doubly magic properties in superheavy nuclei

A systematic study of global properties of superheavy nuclei in the framework of the Liquid Drop Model and the Strutinsky shell correction method is performed. The evolution equilibrium deformations, TRS graphs and α-decay energies are calculated using the TRS model. The analysis covers a wide range of even-even superheavy nuclei from Z =102 to 122. Magic numbers and their observable influence occurring in this region have been investigated. Shell closures appear at proton number Z =114 and at neutron number N =184.

Systematic study of α decay half-lives for even–even nuclei within a deformed two-potential approach

In this work,we systematically study theαdecay half-lives of 196 even–even nuclei using a two-potential approach improved by considering nuclear deformation.The results show that the accuracy of this model has been improved after considering nuclear deformation.In addition,we extend this model to predict theαdecay half-lives of Z=118 and 120 isotopes by inputting theαdecay energies extracted from the Weizsacker–Skyrme-type(WS-type)mass model,a simple nuclear mass formula,relativistic continuum Hartree–Bogoliubov theory and Duflo-Zuker-19(DZ19)mass model.It is useful for identifying the new superheavy elements or isotopes for future experiments.Finally,the predictedαdecay energies and half-lives of Z=118 and 120isotopes are analyzed,and the shell structure of superheavy nuclei is discussed.It shows that the shell effect is obvious at N=184,while the shell effect at N=178 depends on the nuclear mass model.

Stability of super heavy nuclei associated with the updated nuclear data

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