Effects of triaxial deformation on the fission barrier in the Z=118−120 nuclei

By using potential energy surface(PES)calculations in the three-dimensional space(β_(2),γ,β_(4))within the framework of the macroscopic-microscopic model,the fission trajectory and fission barrier for Z=118(Og),119,120 nuclei has been systematically investigated.The calculated PES includes macroscopic liquid-drop energy,microscopic shell correction and pairing correction.Taking the ^(294)Og176 nucleus as an example,we discuss the next closed shell after Z=82 and N=126 with the calculated Woods-Saxon single-particle levels.Then,the results of PES in ^(294)Og is illustrated from the(X,Y)scale to the(β_(2),γ)scale.Theγdegree of freedom reveals the shape evolution clearly during the fission process.The structure near the minimum and saddle point of the PES in the Z=118,119,120 nuclei is demonstrated simultaneously.Based on the potential energy curves,general trends of the evolution of the fission barrier heights and widths are also studied.The triaxial deformation in these superheavy mass regions plays a vital role in the first fission barrier,showing a significant reduction in both triaxial paths.In addition,the model-dependent fission barriers of proton-rich nuclei ^(295)Og,296119,and 297120 are analyzed briefly.Our studies could be valuable for synthesizing the superheavy new elements in the forthcoming HIAF and other facilities.

Discovery of new characterizations of parameter distributions in a semiempirical mass model:an investigation by dividing an overdetermined system into numerous balanced subsystems

We propose and test a new method of estimating the model parameters of the phenomenological BetheWeizsacker mass formula.Based on the Monte Carlo sampling of a large dataset,we obtain,for the first time,a Cauchy-type parameter distribution formed by the exact solutions of linear equation systems.Using the maximum likelihood estimation,the location and scale parameters are evaluated.The estimated results are compared with those obtained by solving overdetermined systems,e.g.,the solutions of the traditional least-squares method.Parameter correlations and uncertainty propagation are briefly discussed.As expected,it is also found that improvements in theoretical modeling(e.g.,considering microscopic corrections)decrease the parameter and propagation uncertainties.