Entrance-channel dynamics in the reaction ~(40)Ca+~(208)Pb

The entrance-channel dynamics including capture, fusion, and quasifission processes for the reaction ~(40)Ca+~(208)Pb is investigated in the fully microscopic time-dependent Hartree-Fock(TDHF) theory. The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions, in which the full Skyrme energy functional SLy4d and SLy5 are adopted.We study the energy dependence of capture cross sections, and find that the experimental data are well reproduced by the TDHF calculations. Both fusion and quasifission events are observed in the reaction ~(40)Ca+~(208)Pb. The contact time, mass and charge of quasifission fragments show a wide distribution in SLy4d compared with SLy5, implying that more nucleons are transferred in the SLy4d calculations. We find that the total kinetic energy of quasifission fragments in the TDHF calculations is distributed around Viola systematics, indicating that most of the relative kinetic energy is dissipated in quasifission dynamics.     

Angular momentum dependence of quasifission dynamics in the reaction <Superscript>48</Superscript>Ca+<Superscript>244</Superscript>Pu

The quasifission dynamics in the reaction ⁴⁸Ca+²⁴⁴Pu is investigated in the framework of time-dependent Hartree-Fock (TDHF) theory. The calculations are performed in three-dimensional Cartesian coordinate without any symmetry restrictions. The full Skyrme energy functional is incorporated in our TDHF implementation. The quasifission dynamics is quite sensitive to the angular momentum of colliding system. The contact time of quasifission decreases as a function of angular momentum and then forms a plateau with small oscillations. The quasifission process is accompanied by an important multi-nucleon transfer. The quantum shell effect plays a crucial role in the mass and charge of quasifission fragments. The mass-angle distribution of the fragments is calculated, which can be compared directly with future experiments.     

Theoretical investigation of the antimagnetic rotation in ~(104)Pd

The particle-number-conserving method based on the cranked shell model is used to investigate the antimagnetic rotation band in ~(104) Pd. The experimental moments of inertia and reduced B(E2) transition probabilities are reproduced well. The J~((2))/B(E2) ratios are also discussed. The occupation probability of each orbital close to the Fermi surface and the contribution of each major shell to the total angular momentum alignment as function of rotational frequency are analyzed. The backbending mechanism of the ground state band in ~(104) Pd is understood clearly and the configuration of the antimagnetic rotation after backbending is clarified. In addition, the crossing of a four quasiparticle state with this antimagnetic rotation band is also predicted. By examining the closing of the angular momenta of four proton holes towards the neutron angular momentum, the "two-shears-like" mechanism for this antimagnetic rotation is investigated and two stages of antimagnetic rotation in ~(104) Pd are clearly seen.     

Fragment distribution in ~(78,86)Kr+~(181)Ta reactions

Within the framework of the isospin-dependent quantum molecular dynamics model, along with the GEMINI model, the ~(86)Kr+~(181)Ta reaction at 80, 120 and 160 MeV/nucleon and the ~(78)Kr+~(181)Ta reaction at 160 MeV/nucleon are studied, and the production cross sections of the generated fragments are calculated. More intermediate and large mass fragments can be produced in the reactions with a large range of impact parameter. The production cross sections of nuclei such as the isotopes of Si and P generally decrease with increasing incident energy.Isotopes near the neutron drip line are produced more in the neutron-rich system ~(86)Kr+~(181)Ta.     

Microscopic description of heavy-ion collisions in terms of interacting RPA modes

Starting from the TDHF equation, the equations of motion for the single-particle density matrices refering to projectile and target are derived in an approximative way in a translating and rotating reference frame. An expansion of the fluctuating part of the transformed density in terms of generalized RPA modes in the ph as well as the pp(hh) channel leads to a system of non-linear coupled equations which simultaneously determine the time development of the collective coordinates and momenta of the relative motion, of the intrinsic angular momentum, and of the amplitudes of coherent surface excitations of the fragments. In a schematic calculation the formalism is applied to the angular momentum dissipation in the excitation of damped giant dipole modes.     

25MeV/u 40)Ar+209Bi裂变反应研究

实验对25MeV/u ⁴⁰Ar+²⁰⁹Bi体系的裂变反应,利用线性动量转移的分窗选择不同的激发能,研究裂变动能分布和质量分布与热核初始激发能的关系.实验证实激发能小于380MeV时裂变总动能分布与低激发能复合核相似.激发能大于380MeV时,最可几动能呈现出随激发增加而增加,并出现高能非对称性,而且质量分布宽度随激发能增加而迅速增大.     

Angular distribution measurement for ~(12)C fragmentation via ~(12)C + ~(12)C scattering at 100 MeV/u

The angular distributions and energy spectra of~(11)B,~(10)B,and~9Be fragments of~(12)C in the angular range from 1.0°~to 7.5°~at 100 Me V/u were obtained via~(12)C+~(12)C scattering.Detailed comparisons are presented between the experimental data and the modified antisymmetrized molecular dynamics(AMD-FM),binary intranuclear cascade model(BIC)and Liege intranuclear cascade model(INCL++).The experimental angular distributions and energy spectra are well reproduced by the AMD-FM calculations but fail to be reproduced by the physical models installed in the Geant4 program,including the BIC and INCL++models.     

Tilted Axis Rotation of ~(57)Mn in Covariant Density Functional Theory

The self-consistent tilted axis cranking covariant density functional theory based on the point-coupling interaction is applied to investigate the tilted axis rotation in ~(57)Mn.The observed data for band C are reproduced well with the assigned configuration config 1.The shears mechanism for magnetic rotation is examined by investigating microscopically the orientation of angular momentum and the corresponding contributions.It is found that config 1 and config 3 correspond to a rotation of high-K character.Config 2 corresponds to a rotation of magnetic character.However,due to the presence of electromagnetic transition B(M1) and B(E2),collective rotation plays an essential role in the competition with magnetic rotation.     

Study of ~3He inelastic scattering on ~(13)C and ~(14)C at 37.9 MeV

The differential cross sections of elastic and inelastic scattering of ³He ions on ¹³C and ¹⁴C have been studied at an energy of 37.9 MeV with a double folding model based on M3Y-Reid effective nucleon-nucleon interaction. The resulted parameters have been used for the standard Distorted Wave Born Approximation calculations of angular distributions corresponding to different excitations levels of ¹³C and ¹⁴C and deformation parameters have been deduced.     

The influence of the entrance channel on the formation and decay of the compound nucleus <Superscript>250</Superscript>No

The mass-energy and angular distributions of binary fissionlike fragments produced in the reactions ⁴⁴Ca + ²⁰⁶Pb and ⁶⁴Ni + ¹⁸⁶W, leading to the same compound nucleus ²⁵⁰No, have been measured at excitation energies of 30 and 40 MeV. The presence of the quasifission component was observed for both systems. But in the case of the ⁶⁴Ni ion, the quasifission process dominates, while in the case of the ⁴⁴Ca ion, the main process is the fusion-fission of compound nucleus ²⁵⁰No. From the angular distributions of reaction fragments, the time scales were found for quasifission and fusion-fission for both reactions.     

Projectile fragment emission in the fragmentation of ~(56)Fe on C,Al and CH_2 targets at 471 A MeV

The emission angle and the transverse momentum distributions of projectile fragments produced in the fragmentation of ⁵⁶Fe on CH₂, C and Al targets at 471 A MeV are measured. It is found that for the same target, the average value and width of the angular distribution decrease with an increase of the projectile fragment charge; for the same projectile fragment, the average value of the distribution increases and the width of the distribution decreases with increasing the target charge number. The transverse momentum distribution of a projectile fragment can be explained by a single Gaussian distribution and the averaged transverse momentum per nucleon decreases with the increase of the charge of projectile fragment. The cumulated squared transverse momentum distribution of a projectile fragment can be explained well by a single Rayleigh distribution. The temperature parameter of the emission source of the projectile fragment, calculated from the cumulated squared transverse momentum distribution, decreases with the increase of the size of the projectile fragment.     

Tangential friction in nuclear reactions studied with the time-dependent Hartree-Fock model

The dissipation of orbital angular momentum is studied by analyzing TDHF calculations of the damped nuclear reaction 280 MeV ⁴⁰Ca+⁴⁰Ca in terms of the nucleon exchange transport model. While the overall results of the TDHF calculation are well accounted for by the NET model, the more detailed behavior reveals evidence of a finite intrinsic nuclear relaxation time.     

Study of symmetry-breaking in TDHF calculations

We analyse, on an numerical calculation of time-dependent Hartree-Fock (TDHF) reaction trayectories for small colliding nuclei, the time variation of linear and angular momentum dispersions. The correlations between the amount of symmetry-breaking in the mean field and the caracteristics of the reaction path are examined.     

Disentangling effects of nuclear structure in heavy element formation

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming 232Cm, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.     

Experimental study of the elastic scattering of ~(10)Be on ~(208)Pb at the energy of around three times the Coulomb barrier

Elastic scattering of 10Be on a 208Pb target was measured at ELab=127 MeV,which corresponds to three times the Coulomb barrier.The secondary 10Be beam was produced at the Radioactive Ion Beam Line in Lanzhou of the Heavy-Ion Research Facility in Lanzhou.The angular distribution of elastic scattering in the 10 Be+208Pb system shows a typical Fresnel diffraction peak.Optical model analysis of the angular distribution was performed using the Woods-Saxon,double-folding and global potentials.With the global potential,different density distributions were used.The results indicate that different density distributions for the projectile induce distinct effects in the angular distribution.     

Angular anisotropy of the fusion-fission and quasifission fragments

The anisotropy in the angular distribution of the fusion-fission and quasifission fragments for the ¹⁶O + ²³⁸U , ¹⁹F + ²⁰⁸Pb and ³²S + ²⁰⁸Pb reactions is studied by analyzing the angular-momentum distributions of the dinuclear system and compound nucleus which are formed after capture and complete fusion, respectively. The orientation angles of the axial symmetry axes of the colliding nuclei relative to the beam direction are taken into account for the calculation of the variance of the projection of the total spin onto the fission axis. It is shown that there is a large contribution of the quasifission fragments in the ³²S + ²⁰⁸Pb reaction to the deviation of the experimental angular anisotropy from the statistical model results. Enhancement of anisotropy at low energies in the ¹⁶O + ²³⁸U reaction is connected with the quasifission of the dinuclear system having low temperature and relatively small effective moment of inertia.     

采用MSDI严格角动量投影46Ti、48Cr形变HF谱

采用修正的表面δ相互作用(MSDI),以球形壳模型单粒子态作基矢,对fp壳层区偶偶核⁴⁶Ti、⁴⁸Cr进行形变Hartree–Fock(HF)计算,并用形变HF单粒子态构造Slater行列式波函数,即形变HF内禀态,然后对其实施严格角动量投影程序,得到比较合理的结果.     

A Common Optical Potential for ~4He+~(12)C at Intermediate Energies

A common optical potential for ~4He+~(12)C at intermediate bombarding energies,which is essential in analyzing exotic nuclei with ~4He clusters,is obtained based on the Sao Paulo potential.Among systematic optical potentials for ~4He+~(12)C,this potential has the merit of using a fixed imaginary part of the Woods-Saxon form.By opticalmodel calculations,this potential reproduces the experimental elastic scattering angular distributions of ~4He+~(12)C well within the energy range of 26A-60 A MeV.It is also applied successfully in calculations of the breakup reactions of ~6Li+~(12)C and ~6He+~(12)C with a three-body continuum discretized coupled-channel method.     

Heavy-ion fusion in classical and semiclassical microscopic approaches

Classical and semi-classical microscopic approaches leading to fusion of two heavy nuclei are studied. Calculations show that the results depend strongly on the nature of the nucleon-nucleon interaction. It is also observed that there is no angular momentum window unlike in TDHF calculations.