对关联对核基态和集体激发态性质的影响

基于相对论平均场和BCS理论,研究了共振连续对奇特核对关联性质的影响. 利用S矩阵方法，通过设定合理的散射态边界条件来得到单粒子共振态的能量和宽度. 通过引入连续态能级密度的方法来处理共振态宽度对核对关联的贡献. 计算结果显示合理地处理共振态对对关联性质的贡献在研究滴线附近核性质时很重要. 它可以影响中子的对隙、费米能级、对关联能以及总结合能. 其次,基于RMF+BCS基态,采用线性响应理论给出了描述开壳核集体激发态性质的准粒子相对论无规位相近似理论. 并且将该方法应用于开壳核120Sn的各种同位旋标量集体激发态性质的研究中. 研究表明：对关联对核的集体激发性质的影响主要表现在低能集体激发态上,考虑对关联后的相对论无规位相近似理论能够很好地再现低能集体激发的实验结果.     

Effect of resonant continuum on pairing correlations in the relativistic approach

A proper treatment of the resonant continuum is to take account of not only the energy of the resonant state, but also its width. The effect of resonant states on pairing correlations is presented in the framework of the relativistic mean-field theory plus Bardeen-Cooper-Schrieffer (BCS) approximation with a constant pairing strength. The study is performed in an effective Lagrangian with the parameter set NL3 for neutron-rich even-even Ni isotopes. Results show that the contribution of the proper treatment of the resonant continuum to pairing correlations for those nuclei close to the neutron drip line is important. The pairing gaps, Fermi energies, pairing correlation energies, and binding energies are considerably affected by a proper consideration of the width of resonant states. The problem of unphysical particle gas, which may appear in the calculation of the traditional mean field plus BCS method for nuclei in the vicinity of the drip line could be well overcome when the pairing correlation is performed by using the resonant states instead of the discretized states in the continuum.PACS: 21.60.-n Nuclear-structure models and methods - 24.10.Jv Relativistic modelsZhong-Yu Ma: Also at Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator of Lanzhou, Lanzhou 730000, PRC and Institute of Theoretical Physics, Beijing 100080, PRC.     

Gamow shell model description of neutron-rich nuclei

This work presents the first continuum shell-model study of weakly bound neutron-rich nuclei involving multiconfiguration mixing. For the single-particle basis, the complex-energy Berggren ensemble representing the bound single-particle states, narrow resonances, and the nonresonant continuum background is taken. Our shell-model Hamiltonian consists of a one-body finite potential and a zero-range residual two-body interaction. It is demonstrated that the residual interaction coupling to the particle continuum is important; in some cases, it can give rise to the binding of a nucleus.     

Clusters as Many-Body Resonances

A formalism to evaluate the resonant states produced by two particles moving outside a closed shell core is presented. The two-particle states are calculated by using a single-particle representation consisting of bound states, Gamow resonances and scattering states in the complex energy plane (Berggren representation). Two representative cases are analysed corresponding to whether the Fermi level is below or above the continuum threshold. It is found that long-lived resonances are mostly determined by either bound states or by narrow Gamow resonances. However, they are significantly affected by wide resonances and the continuum background itself.     

Resonant Continuum in Extended RMF Plus BCS Approximation

The contribution of the resonant continuum to pairing correlations is investigated in the relativistic mean field theory plus Bardeen-Cooper-Schrieffer (BCS) approximation with a constant pairing strength. The resonance states with their widths in the continuum are considered explicitly. The numerical study is performed in an effective Lagrangian with the parameter set NLSH for neutron-rich nucleus ⁸⁴Ni. The results show that the effect of the proper treatment of the resonant continuum on pairing correlations for nucleus close to neutron drip line is important. It is found that the problem of an unphysical particle gas could be overcome when the pairing correlation is performed by using the resonant states instead of the discretized states in the continuum.     

Study of theS-matrix near bound states in the continuum

The behaviour ofS-matrix for potentials generating bound states in continuum in the neighbourhood of the positive bound state energies is studied. It is shown that unlike the case of usual negative energy bound states, theS-matrix does not have a pole at the positive bound state energy but becomes unity at the energy corresponding to bound states in continuum. Calculations ofS-waveS-matrix for a local potential constructed by Stillinger and Herrick and a separable nonlocal potential constructed by the present authors verify these results. Our results indicate that the bound states embedded in continuum constructedvia the von Neumann and Wigner procedure cannot be interpreted as resonances with zero width.     

Borromean three-body heteroatomic resonances

We present an approach to analyze recent experimental evidences of Efimov resonant states in mixtures of ultracold gases, by considering two-species three-body atomic systems bound in a Borromean configuration, where all the two-body interactions are unbound. For such Borromean three-body systems, it is shown that a continuum three-body s-wave resonance emerges from an Efimov state as a scattering length or a three-body scale is moved. The energy and width of the resonant state are determined from a scaling function with arguments given by dimension-less energy ratios relating the two-body virtual state subsystem energies with the shallowest three-body bound state. The peculiar behavior of such resonances is that their peaks are expected to move to lower values of the scattering length, with increasing width, as one raises the temperature. For Borromean systems, two resonant peaks are expected in ultralow-temperature regimes, which will disappear at higher energies. It is shown how a Borromean-Efimov excited bound state turns out to a resonant state by tuning the virtual two-body subsystem energies or scattering lengths, with all energies written in units of the next deeper shallowest Efimov state energy. The resonance position and width for the decay into the continuum are obtained as universal scaling functions (limit cycle) of the dimensionless ratios of the two and three-body scales, which are calculated numerically within a zero-range renormalized three-body model.     

Pauli blocking in degenerate plasmas and the separable potential approach

The Mott effect describes the dissolution of bound states in a dense partially ionized plasma. It occurs when the ionization potential depression, owing to effects of correlation and degeneracy, compensates the binding energy of the bound state. At high densities and moderate temperatures, the Pauli blocking becomes important and influences significantly the degree of ionization in the region of degenerate plasmas. A quantum statistical approach is used where the total density is decomposed in an uncorrelated, “free” part and correlations, as a consequence of the cluster decomposition of the self‐energy. The contribution of correlations to the total density is given by bound states and continuum correlations. Exact solutions for a separable potential are compared to perturbation theory and numerical solutions of the in‐medium Schrödinger equation. The in‐medium scattering phase shifts are evaluated, and the role of continuum correlations is discussed. The Pauli blocking of bound states and the density of states are considered for warm dense matter conditions.     

New method for extracting quasi-bound states from the continuum

A new parameter-free method is proposed for treatment of single-particle resonances in the real-energy continuum shell model. This method yields bound states embedded in the continuum, the anamneses of resonances, which provide a natural generalization of weakly bound single-particle states.     

Pygmy and Giant Dipole Resonances in Proton-Rich Nuclei ~(17,18)Ne

The pygmy and giant dipole resonances in proton-rich nuclei~(17,18)Ne are investigated with a fully self-consistent approach. The properties of ground states are calculated in the Skyrme Hartree-Fock with the Bardeen-CooperSchrieffer approximation to take into account the pairing correlation. The quasiparticle random phase approximation(QRPA) method is used to explore the properties of excited dipole states. In the calculations the SLy5 Skyrme interaction is employed. In addition to the giant dipole resonances, pygmy dipole resonances(PDR) are found to be located in the energy region below 10 MeV in both 17,18 Ne. The strength and transition density show that the low-lying states are typical PDR states. However, analyzing the QRPA amplitudes of proton and neutron 2 quasiparticle(2 qp) configurations for a given low-lying state in ~(17,18)Ne, we find that the PDR state is less collective, more like a single 2 qp excitation.     

Some Aspects of Nuclear Structure in Relativistic Approach

The nucleon effective interaction in the nuclear medium is investigated in the framework of the DiracBrueckner-Hartree-Fock (DBHF) approach. A new decomposition of the Dirac structure of nucleon self-energy in the DBHF is adopted for asymmetric nuclear matter. The properties of finite nuclei are investigated with the nucleon effective interaction. The agreement with the experimental data is satisfactory. The relativistic microscopic optical potential in asymmetric nuclear matter is investigated in the DBHF approach. The proton scattering from nuclei is calculated and compared with the experimental data. A proper treatment of the resonant continuum for exotic nuclei is studied. The width effect of the resonant continuum on the pairing correlation is discussed. The quasiparticle relativistic random phase approximation based on the relativistic mean-field ground state in the response function formalism is also addressed.     

Some Aspects of Nuclear Structure in Relativistic Approach

The nucleon effective interaction in the nuclear medium is investigated in the framework of the DiracBrueckner-Hartree-Fock (DBHF) approach. A new decomposition of the Dirac structure of nucleon self-energy in the DBHF is adopted for asymmetric nuclear matter. The properties of finite nuclei are investigated with the nucleon effective interaction. The agreement with the experimental data is satisfactory. The relativistic microscopic optical potential in asymmetric nuclear matter is investigated in the DBHF approach. The proton scattering from nuclei is calculated and compared with the experimental data. A proper treatment of the resonant continuum for exotic nuclei is studied. The width effect of the resonant continuum on the pairing correlation is discussed. The quasiparticle relativistic random phase approximation based on the relativistic mean-field ground state in the response function formalism is also addressed.     

奇特核结构与激发的微观研究

原子核是一个从少体到多体过渡的量子体系,展现了很多有趣的集体现象。随着国际上若干大型放射性核束流实验装置的发展,极不稳定奇特核的结构与激发的研究成为当前核物理的前沿热点问题。本工作以形变弱束缚核40Mg为例,基于格点空间连续谱能量密度泛函和自洽的FAM-QRPA对奇特核的基态与激发态跃迁进行了研究。发现弥散的表面密度分布与连续谱对低能共振有很大影响。通过对同位旋矢量偶极激发的研究,说明低能矮共振与巨共振的微观机制有很大差异。此外还进行了大规模拟合,发展针对丰中子核,超重核的新的高精度有效相互作用,以期为相关学科如核天体物理、核裂变能等提供更为可靠的核理论模型。Nuclei are quantum systems in the evolution from few-body to many-body systems, and can exhibit many amazing collective phenomena. With the development of several advanced radioactive-beam facilities, the study of structures and excitations of extreme unstable exotic nuclei has become a hot issue. In this work, we solve the self-consistent FAM-QRPA in large deformed coordinate-spaces to treat continuum effects. We study properties of structures and collective excitations in deformed drip-line nuclei. We found that in weakly bound nuclei 40Mg, the diffuse surface density and pairing density play an important role in low-lying resonance. Through analysis of deformation-induced K-splitting in isovector dipole modes, we see that pygmy resonances have very different mechanism compared to giant resonances. In addition, large-scale fittings are performed to develop highprecision effective interactions, which will provide more reliable theoretical model for related subjects, such as nuclear astrophysics and nuclear fission energy.     

Self-Consistent Description of Isobaric Analog Resonances in Neutron-Rich Nuclei with Pairing

Physics of Atomic Nuclei - A self-consistent approach to describing isobaric analog resonances (IAR) in neutron-rich nuclei that involve pairing is developed. The continuum quasiparticle...     

Two-particle resonant states in a many-body mean field

A formalism to evaluate the resonant states produced by two particles moving outside a closed shell core is presented. It is found that long lived two-body states (including bound states) are mostly determined by either bound single-particle states or by narrow single-particle resonances. However, they can be significantly affected by the continuum part of the spectrum.     

Phase modulated thermal conductance of Josephson weak links

We present a theory for quasiparticle heat transport through superconducting weak links. The thermal conductance depends on the phase difference (phi) of the superconducting leads. Branch-conversion processes, low-energy Andreev bound states near the contact, and the suppression of the local density of states near the gap edge are related to phase-sensitive transport processes. Theoretical results for the influence of junction transparency, temperature, and disorder, on the conductance, are reported. For high-transmission weak links, D-->1, the formation of an Andreev bound state leads to suppression of the density of states for the continuum excitations, and thus, to a reduction in the conductance for phi approximately pi. For low-transmission (D<1) barriers resonant scattering leads to an increase in the thermal conductance as T drops below T(c) (for phase differences near phi=pi).     

The quasibound state model for self-consistent characteristics of semiconductor intersubband devices

The quasibound state model (QBSM) for determining the self-consistent conduction band profile and space charge density of semiconductor intersubband devices is presented. This new method is based on the quasibound (QB) state resonances of quantum structures. For heterostructures, the traditional self-consistent energy continuum model (ECM) calculates space charge by integration over the entire energy continuum, weighted by Fermi–Dirac statistics. In the present approach, the continuum of energy states of the heterostructure is accurately represented by a small number of QB states, and the space charge calculations are performed only at these eigen-energies. This approach significantly reduces the computational burden associated with all self-consistent algorithms. Theoretical formulation of QBSM is compared with the traditional ECM approach. The bound (B) and QB eigenenergies of the structure are obtained by solving the single-band effective-mass Schrödinger equation using the argument principle method. The performance and the accuracy of the QBSM are evaluated for a double-barrier resonant structure and an asymmetric Fabry–Perot electron-wave interference filter. The self-consistent electron density and potential profiles calculated by the present method are shown to be in excellent agreement with the results obtained from the traditional ECM model. In addition to requiring less computational time, the present method is easily implemented and may be applied equally well to biased/unbiased, symmetric/asymmetric heterostructures.     

The influence of absorption on possible nucleon-antinucleon resonances and bound states

We study analytically the effect of an absorptive potential on bound states and resonances in the N$\text{N}$ system. We show that these states are destroyed by moderate absorption. Thus, only N$\text{N}$ channels which are weakly absorptive can exhibit resonant behaviour.