| Fission has been one of the most important motion in nuclear theory for a long time.In general,the nuclear fission is defined as the process of heavy nuclei divided into several medium fragments.Up to date,the study of fission and its mechanism still dominate one of the hottest topics in nuclear physics.In fact,to accurately describe the fission process is directly related to the investigation of the fusion and fission of superheavy nuclei,which would be helpful to search for the limit of superheavy nuclei.On the other side,the nuclei with mass number A?60 could survive from fusion and charged particle capture reaction in nuclear astrophysics.However,for A>60,they should depend on the slow process(s-process)and rapid process(r-process).The analysis on fission barrier is the key of the study of r-process.Accordingly,in the framework of macroscopic-microscopic model and based on the cranked shell model,we have systematically investigated the effects of various degrees of freedom(e.g.,?2,?,?4,Z,N,?)on fission barrier in tranuranium nuclei by the pairing-deformation-frequency self-consistent total-Routhian-surface(TRS)calculations.In addition,comparing to the ?-stable nuclei,there are many int,eresting phenomena in the nuclei near the drip lines or at the high-spin states,such as shape coexistence,the backbending of moments of inertia,shape evolution and collective motion phase evolution.Therefore,in the present work,we have analyzed the mechanism behind these collective phenomena more detailedly in the N= 104 midshell isotones with strong collectivity.To begin with,taking the heavier 252Cf nucleus(with the available empirical fission barrier from experiment)as an example,we have displayed our result and other works,together wit,h a brief discussion.It is found that our calculation shows a good agreement with experimental data by only?30 keV overestimate,which favoured remarkably to some extent.By separating the macroscopic energy and microscopic energy(shell correction energy and pairing correction energy),it indicates that the trend of total potential energy curve is consistent with the mi-croscopic one.Furthermore,it implies that the shell correction energy dominates the evolution of microscopic energy.With respect to the structure of single-particle levels,the energy on triaxial saddle is lower than the axial saddle,which leads to the reduction of the first fission barrier on triaxial saddle.In addition,by virtue of the error analysis on 13 empirical fission barrier between experiment and our work,it is found that the present multi-dimensional potential energy surface calculations could describe finely well the first fission barriers in actinide nuclei.Therefore,we also illustrate the shape of fission barriers in 95 transuranium nu-clei,which has been filled with the blank investigation of the systematic research.Besides,we have extracted the height of the first fission barrier in these nucle-i,awaiting experimental confirmation in future.For the nuclei with N = 152 subshell,they are exhibited with well rotational properties and located in the transition region from heavy nuclei to superheavy region.Thus,they are suited for the research of the effects of various deformations on the first fission barrier by the present method.According to the evolution of the potential energy curves versus main deformation ?2 in these isotones,it reveals that the macroscopic en-ergies are negative after Z= 104,i.e.,the superheavy nuclei do survive due to the microscopic energy.Moreover,comparing to the effect of ? deformation on fission barrier,the influence of ?4 deformation is relatively small but not be able to neglected.Indeed,the potential energy curves with ?4 in N=152 isotones are depicted an oscillating behavior in contrast to without ?4.It has pulled down the minima and pushed up the saddle of potential energy curves.The mecha-nism behind this interesting phenomenon has been explained by single-particle levels in 148Cm.For the effect of model parameters on the first fission barrier,we briefly discussed the modification of Woods-Saxon(WS)parameters and pairing strength in 254Rf near the proton-drip line.In addition,based on the shape of fission barrier in 95 transuranium nuclei previously,we select several isovolumic nuclei with mass number A=256 to exemplify the triaxiality and Coriolis effects on the first fission barrier,together with the contribution of each part to the height of fission barrier.Meanwhile,by using the empirical quantities R4/2,P-factor and the results by other model,it is found that these nuclei are represented similar collective characteristics.Then,with the increasement of rotational fre-quency,the pairing gaps seem to decrease markedly,indicating the reduction of pairing correction.It is also found that the contribution of shell correction energy still play an important role on the first fission barrier.For the anormal shape of fission barrier at higher spins,they may be attribut.ed to the banding crossing.A convenient way to survey this issue is to achieve their moments of inertia.Based on the TRS calculations,we have reproduced well the behavior of moments of inertia in 256Fm and 256Rf.Generally,there are similar upbendings in these isovo-lumic nuclei.However,the upbendings arise more abrupt and strongly in nuclei with the light proton numbers.From the quasiparticle diagram near the Fermi surface in 256Cm,there is a crossing between a pair of quasiproton Routhians.It is suggested that these protons turn to be de-coupling and thus two quasiproton configuration occupies the yrast state.As a result,the behavior of moments of inertia increases suddenly.For the rotational properties of N=104 midshell isotones,we start with the observed shape coexistence bands in 186Pb,184Hg and 182Pt.By studying the evo-lution of single-particle levels versus deformation parameters,we demonstrate the shape coexistence of oblate,prolate and superdeformed prolate in 181Hg carefully.Moreover,after the research on the whole N = 104 isotones,we have proposed several rotational frequency optimally to observe the shape coexistence.Besides,we have explained the backbending of moments of inertia in these nuclei with well rotational characteristics.In the defective reproduction of the behaviors in MOI after the adjustment of the pairing strength,it maybe ascribes to the mean field in the present calculation,which has not considered the rotational-vibrational cou-pling.Indeed,based on several improved E-gamma over spin(E-GOS)curves,we have suggested that the evolution between the collective rotational mode and vibrational mode in these nuclei as well.Furthermore,it seems that the stiff-ness of potential energy surface is corresponding to t he collective motion mode to some extent.Finally,the evolution of single-particle levels versus WS parameters has been given systema.tically in 188Po,which is the heaviest N = 104 isotones near the proton-drip line.The modification of WS potential parameters V and r0 would pull up the single-particle levels or push down them,whereas the effects of ?,r0 sp and a could change the order of them.These results are useful to fit WS parameter set in drip-line nuclei and superheavy nuclei in future. |
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