Z=50—71核质量与核形状跃变

对Johansson质量公式的某些参数及β方程进行修改;在50≤Z≤71区域,计算了640个原子核的质量和双中子分离能.理论值与实验值相比,方均根误差分别为0.827MeV和0.406MeV.双中子分离能理论曲线很好地重现了N=82的中子满壳层效应和N>90时原子核发生大形变的特性.     

Effective Masses of Pentaquark Θ+ in Nuclear Matter

The properties of baryons in nuclear matter are analysed in the relativistic mean-field theory(RMF). It is found that the scalar field σ meson affects the properties of baryon at high density. A density dependent scalar coupling gσN is determined according to the idea of quark-meson coupling model and extended to RMF. It is shown that gσN affects the property of nuclear matter weakly at low density, but strongly at high density. The relation between the scalar density ρ_S and the nuclear density ρ and the effective mass of the pentaquark Θ⁺ are studied with the density dependent coupling constant. The density dependent scalar coupling obviously affects the effective masses of baryons in nuclear matter, especially at high density.     

Critical Behavior in Nuclear Structure from Spherical to γ-Soft Deformed Shape in IBM

Comparing with the predictions of the transitional dynamical symmetry E（5） proposed by Iachello [Phys. Rev. Lett. 85 （2000） 3580], the critical behaviors from U（5）-0（6） are studied in the space of two control parameters in the interacting boson model. A simple shape phase diagram has been presented. It is found that E（5） predictions cannot be exactly reproduced by our calculations and that the best agreement is close to the calculations with boson number N = 9. By comparing with experimental data on E（5）-like nuclei, we find that E（5） predictions and IBM calculations can reproduce the energy ratios and E2 transition ones.     

Shape coexistence around the Z=82 closed shell probed by α-decay

Shape coexistence around the Z=82 closed proton shell, probed via the fine structure in the α-decay of even–even nuclei, is discussed. The power of α-decay studies is demonstrated by presenting the results from a number of decay experiments of Rn isotopes performed at ISOLDE. The total body of experimental evidence on α-decay of even–even nuclei in the Pb region is used to illuminate, through the α-decay reduced widths of the ground state to ground state transitions and through the hindrance factors of the fine structure, the role of multi-particle multi-hole proton excitations across the Z=82 shell. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure of Hamiltonian Matrix and the Shape of Eigenfunctions：Nuclear Octupole Deformation Model

The structure of a Hamiltonian matrix for a quantum chaotic system,the nuclear octupole deformation model,has been discussed in detail.The distribution of the eigenfunctions of this system expanded by the eigenstates of a quantum integrable system is studied with the help of generalized Brillouin-Wigner perturbation theory.The results show that a significant randomness in this distribution can be observed when its classical counterpart is under the strong chaotic condition.The averaged shape of the eigenfunctions fits with the Gaussian distribution only when the effects of the symmetry have been removed.     

Pairwise Entanglement and Quantum Phase Transitions in Spin Systems

We examine several well-known quantum spin models and categorize the behaviour of pairwise entanglement at quantum phase transitions. A unitied picture on the connection between the entanglement and quantum phase transition in spin systems is presented.     

Research on Level Structures of Neutron-Rich Nuclei and Shape Phase Transitions Around A～100 and 150 Regions

Level structures of neutron-rich even-even nuclei around A～100 and 150 regions have been studied by observing the prompt gamma rays from the spontaneous fission of ²⁵²Cf.The highest spin is up to 10～14.The character of nuclear structures and shape phase transitions of some isotope chains are discussed.     

Novel Transitions in Doped Mott—Insulator KxCoO2

By measuring the temperature dependence of the magnetic susceptibility,two distinct transitions have been observed in potassium doped cobalt oxide KxCoO2(x=0.2-1.0).The transition around 125K corresponds to a phase transition between a weak ferromangnetic plus a strong superparamagnetic phase(below 125K) and a superparamagnetic phase(above 125K).The susceptibility above the Curie point Tc cannot be described by the Curie-Weise law,being consisten with the superparamagnetism.Mangnetizaiton-hysteresis-loops have been measured in different temperature regions to uncover the underlying physics.The second transition near 30.8k shows a strong novelty.     

Transitions between À and 0 states in superconductor-ferromagnet-superconductor junctions

Experimental and theoretical study of superconductor-ferromagnet-superconductor junctions (SFS junctions) showed that, in a certain range of parameters (e.g., the length of the ferromagnet d_F, the exchange field E_ex), the ground state of the SFS junction corresponds to a superconducting phase difference π or 0. The phase diagram of an SFS junction with respect to π and 0 states is investigated in this letter in E_ex, d_F, T space. It is shown that the phase diagram is very sensitive to the geometry of the system, in particular, to the amount of disorder in the junction.     

Masses and Sigma Terms of Pentaquarks in Chiral Perturbation Theory

Assuming that the recently θ＋ and other exotic resonances belong to the pentaquark i0 of SU（3）I with J^P = 1/2, we constructed a relativistic effective lagrangian in the frame work of baryon chiral perturbation theory. The masses of pentaquarks under isospin symmetry is determined by calculating the propagator to one loop, where the extended on-mass-shell renormalization scheme is applied. Using the experimental data for masses of θ＋, Ξ and N, we estimated the mass of Σ and the a terms.     

Relation Between CPT Violation in Neutrino Masses and Mixings

The neutrino parameters determined from the solar neutrino data and the anti-neutrino parameters determined from KamLAND reactor experiment are in good agreement with each other. However, the best fit points of the two sets differ from each other by about 10⁻⁵ eV² in mass-square difference and by about 2° in the mixing angle. Future solar neutrino and reactor anti-neutrino experiments are likely to reduce the uncertainties in these measurements. This, in turn, can lead to a signal for CPT violation in terms a non-zero difference between neutrino and anti-neutrino parameters. In this paper, we propose a CPT violating mass matrix which can give rise to the above differences in both mass-squared difference and mixing angle and study the constraints imposed by the data on the parameters of the mass matrix.     

Anomaly in the Charge Radii and Nuclear Structure

The axially deformed relativistic mean field theory is applied to study the isotope shift of charge distributions of odd-Z Pr isotope chain. The nuclear structure associated with the shell and the isotope effect is investigated. The mechanism of the kink in the isotope shift at the neutron magic number N = 82 is revealed to be dependent on the neutron energy level structure at the Fermi energy, demonstrating that the spin-orbit coupling interaction and p-n attraction are well described by the relativistic mean field theory.     

Magnetic Transitions and Magnetoresistance of Y1—xDyxMn6Sn6（x=0.2 and 0.3）

Magnetic transitions and magnetoresistance of HfFe6Ge6-type Y1-xDyxMn6Sn6 (x=0.2 and 0.3) have been investigated in the temperature range of 5-380K. It was found that the strong exchange interaction between the Dy and Mn sublattices results in incomplete ferromagnetism at low temperatures. At higher temperatures, the metamagnetic transition from an antiferromagnetic state to a ferrimagnetic state can be induced by a fairly small threshold field or by increasing temperature. The magnetic transition is accompanied by a large magnetoresistance effect of about -29% and -16% at 5K for x=0.2 and 0.3, respectively.     

Influence of Nuclear Deformation on the Potential Energy Surface in Di—Nuclear Model

Influence of the nuclear deformation on the potential energy surface(PES) in a di-nuclear system is studied in details.It is found that the PES shape changes greatly due to the deformation effect.The top point of the PES could be reduced significantly,which implies that the optimum excitation energy could also be reduced greatly and may enhance the fromation probability of the compound nucleus.The dynamical deformaiton as a function of the reaction time in the reaction process is dramatic.The Z/N ratios of fragments tend to follow that of the compound nucleus during the nucleon exchange process,but to fluctuate.     

The Nuclear Spin Scissors Mode—Theory and Experiment

A new type of nuclear collective motion—the spin scissors mode—was predicted seven years ago. Promising signs of its existence in ²³²Th were found. We perform a systematic analysis of experimental data on M1 excitations in rare earth nuclei to find traces of the spin scissors mode in this area. Obvious signs of its existence will be demonstrated. We propose new criteria to attribute the observed 1⁺ states to the scissors mode, entailing that the agreement of the experimental data with the results of our calculations and with the sum rules is improved substantially.