Semi-empirical formulae for Λ-binding energy in hypernuclei using mass distribution

Semi-empirical formulae for ground state Λ-binding energy of heavy hypernuclei, in inverse powers of the mass number, using the mass distribution in the folding model, under fairly reasonable assumptions about the range of the Λ-nucleon force are obtained in more than one plausible way. However, they are found to give nearly identical results. A reasonable estimate of the Λ well-depth is obtained from a chi-square fit of the available ground state Λ-binding energy data of medium and heavy nuclei.     

A systematic study on the binding energy of A hypernuclei

We calculate the binding energy per baryon of the A hypernuclei systematically, using the relativistic mean field theory （RMF） in a static frame. Some similar properties are found for most of the A hypernuclei confirmed by experiments. The data show that a A hypernueleus will be more stable if it is made by adding a A hyperon to a stable normal nuclear core, or by replacing a neutron by a A hyperon to a stable normal nuclear core. According to our calculations, the existence of some new A hypernuclei are predicted under the frame of RMF.     

Nuclear energy density functional from chiral pion-nucleon dynamics: Isovector terms

We extend a recent calculation of the nuclear energy density functional in the framework of chiral perturbation theory by computing the isovector surface and spin-orbit terms: ([(?)\vec] r_p - [(?)\vec] r_n\vec \nabla \rho _p - \vec \nabla \rho _n )² G _d(r \rho) + ([(?)\vec] r_p - [(?)\vec] r_n\vec \nabla \rho _p - \vec \nabla \rho _n ·([(J)\vec]_p - [(J)\vec]_n\vec J_p - \vec J_n )G _so(r \rho) + ([(J)\vec]_p - [(J)\vec]_n\vec J_p - \vec J_n )² G _J(r \rho) pertaining to different proton and neutron densities. Our calculation treats systematically the effects from 1p \pi -exchange, iterated 1p \pi -exchange, and irreducible 2p \pi -exchange with intermediate D \Delta -isobar excitations, including Pauli-blocking corrections up to three-loop order. Using an improved density-matrix expansion, we obtain results for the strength functions G _d(r \rho) , G _so(r \rho) and G _J(r \rho) which are considerably larger than those of phenomenological Skyrme forces. These (parameter-free) predictions for the strength of the isovector surface and spin-orbit terms as provided by the long-range pion-exchange dynamics in the nuclear medium should be examined in nuclear structure calculations at large neutron excess.     

核能与聚变裂变混合能源堆

未来20年将是核能发展的一个关键时期.2035年左右,快堆有望投入商用;磁约束聚变、激光聚变、 Z箍缩聚变也都有演示堆计划.聚变演示堆存在纯聚变与聚变裂变混合能源堆两种可能,而后者可降低聚变功率,缓解高能中子对材料的辐照损伤.另外,氘氚聚变供能时间有限.文章介绍了混合能源堆的概念.能源堆可充分利用铀资源,且后处理不涉及铀钚分离,有很好的防扩散性能.裂变堆、聚变堆、能源堆共同发展,可望使核能在不太长的时间内获得大规模应用,并可为人类提供千年以上的能源供应.     

核能与聚变裂变混合能源堆

未来20年将是核能发展的一个关键时期.2035年左右,快堆有望投入商用;磁约束聚变、激光聚变、Z箍缩聚变也都有演示堆计划.聚变演示堆存在纯聚变与聚变裂变混合能源堆两种可能,而后者可降低聚变功率,缓解高能中子对材料的辐照损伤.另外,氘氚聚变供能时间有限.文章介绍了混合能源堆的概念.能源堆可充分利用铀资源,且后处理不涉及铀钚分离,有很好的防扩散性能.裂变堆、聚变堆、能源堆共同发展,可望使核能在不太长的时间内获得大规模应用,并可为人类提供千年以上的能源供应.     

中能重离子碰撞中晕核反应动力学

基于同位旋相关量子分子动力学研究了中子晕核和质子晕核的核反应动力学，着重研究了松散的晕结构对于重离子碰撞中的碎裂和动量耗散中的特殊作用. 为了突出晕核松散结构在反应动力学中的特殊作用. 同时计算了在完全相同入射道条件下相等质量稳定弹核引起核反应. 通过对晕核和稳定核核反应动力学结果的对比分析，发现晕核的松散结构对核反应动力学的作用和影响是重要的. 如这种松散结构明显的增加了碎裂多重性；相反, 减小了原子核阻止(动量耗散). 关键词： 中子晕核 质子晕核 重离子碰撞 核反应动力学     

Nuclear fluid dynamics

For energies where the mean free nucleon path is comparable to the nuclear size, there is no fast local relaxation in nuclear collective motion. Therefore, in a fluid-dynamical approach, the intrinsic energy-density functional must take the distortion of the local Fermi surface into account. This can be achieved by a dynamical Thomas Fermi method which leads to additional restoring forces for the collective modes, except for the casesL=0 andL=1 where usual hydrodynamics is sufficient.     

Beyond mean-field approach for pear-shaped hypernuclei

We develop both relativistic mean field and beyond approaches for hypernuclei with possible quadrupole-octupole deformation or pear-like shapes based on relativistic point-coupling energy density functionals. The symmetries broken in the mean-field states are recovered with parity, particle-number and angular momentum projections. We take_Λ~(21)Ne as an example to illustrate the method, where the Λ hyperon is put on one of the two lowest-energy orbits(labeled as Λ_s, Λ_p), respectively. We find that the Λ hyperon in both cases disfavors the formation of a reflection-asymmetric molecular-like~(16)O+α structure in~(20)Ne, which is consistent with the Nilsson diagram for the hyperon in(β_2, β_3) deformation plane. In particular, we show that the negative-parity states with the configuration~(20)Ne(K~π= 0~-)  Λ_s are close in energy to those with the configuration~(20)Ne(K~π= 0~+)Λ_p, even though they have very different structures. The Λ_s(Λ_p) becomes more and more concentrated around the bottom(top) of the"pear" with the increase of octupole deformation.     

Nuclear core in hypernuclear structure

Hypernuclear structure models are briefly reviewed. Phenomena related to hypernuclear polarization are displayed. A discussion is given of nuclear and hypernuclear neutron orbitals extraction. Preliminary results on ^– angular distributions for the reaction⁶Li(K ^–, ^–) ⁶ Li are presented.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.The collaboration of Dr. M. Sotona and Dr. L. Majling in the speedy preparation of the AD results and discussions with them and with Prof. B. Povh are greatly acknowledged.     

Nuclear reactions with core excitation

The transition amplitudes for nucleon scattering, stripping, pick-up, and break-up reactions are derived in the framework of a three-body model. The model consists of two nucleons and a core. The core is assumed to have a discret excitation spectrum. The nucleon-core interactions give rise to the excitation and subsequent deexcitation of the core. The energy averaged transition amplitudes are obtained by iteration from Faddeevtype integral equations. The lowest order terms correspond to the DWBA and the higher order terms describe the multistep processes.     

Recalibration of the binding energy of hypernuclei measured in emulsion experiments and its implications

The Λ separation energy for Λ hypernuclei,denoted B_Λ,measured in 1967,1968,and 1973 are recalibrated using the current best estimates of the mass of particles and nuclei.The recalibrated B_Λ are systematically larger(except in the case of _Λ~6He) than the originally published values by about 100 keV.The effect of this level of recalibration is very important for light hypemuclei,especially for the hypertriton.The early B_Λ values measured in1967,1968,and 1973 are widely used in theoretical research,and the new results provide better constraints for the conclusions of such studies.     

High energy limit in rearrangement collisions

The cross section for particle exchange from ground state to ground state in a three-particle collision is investigated. An asymptotic expansion for high incident energies can be given if the Fourier transforms of the interaction potentials allow an expansion in powers of 1/k for largek, which includes Coulomb interaction. It is shown that in general the first and second Born approximations provide the asymptotically leading terms. For special mass ratios, scattering into special (critical) angles becomes predominant. These angles, which are independent of energy, can also be determined employing classical arguments. Near the critical angles single terms of either the first or second Born approximation become dominant. If the exchanged mass is small, the interaction between the two heavy masses cancels near forward direction, implying the validity of the impact parameter theory. The results are discussed for Coulomb interaction as the simplest example (electron exchange). Here, the contributions by critical scattering are small unless the energies become exceedingly large.     

Study of ΛΛ dynamics and ground state structure of low and medium mass double Λ hypernuclei

We critically review the ΛΛ dynamics by examining Λ - Λ and Λ-nucleon phenomenological potentials in the study of the bound state properties of double-Λ hypernuclei _ΛΛ ⁶ He, _ΛΛ ¹⁰ Be, _ΛΛ ¹⁴ C, _ΛΛ ¹⁸ O, _ΛΛ ²² Ne, _ΛΛ ²⁶ Mg, _ΛΛ ³⁰ Si, _ΛΛ ³⁴ S, _ΛΛ ³⁸ Ar, _ΛΛ ⁴² Ca, _ΛΛ ⁴⁶ Ti, _ΛΛ ⁵⁰ Cr, _ΛΛ ⁵⁴ Fe, _ΛΛ ⁵⁸ Ni, _ΛΛ ⁶² Zn, _ΛΛ ⁶⁶ Ge, _ΛΛ ⁷⁰ Se, _ΛΛ ⁷⁴ Kr, _ΛΛ ⁷⁸ Sr, _ΛΛ ⁸² Zr, _ΛΛ ⁸⁶ Mo, _ΛΛ ⁹⁰ Ru, _ΛΛ ⁹⁴ Pd, _ΛΛ ⁹⁸ Cd, _ΛΛ ¹⁰² Sn in the frame work of (core+Λ+Λ) three body model. An effective ΛN potential is obtained by folding the phenomenological ΛN potential into the density distribution of the core nuclei. The former two cases (i.e. _ΛΛ ⁶ He and _ΛΛ ¹⁰ Be) are revisited to justify the correctness of the present potential model. Assuming the same potential model we predicted some of the structural properties of heavier doubly Λ-hypernuclei. The hyperspherical harmonics expansion method, which is an essentially exact method has been employed for the three body system. A convergence in binding energy up to 0.15% for K _max=20 has been achieved. In our calculation we have made no approximation in restricting the allowed l-values of the interacting pairs.     

Nuclear quantum many-body dynamics

A summary of recent researches on nuclear dynamics with realistic microscopic quantum approaches is presented. The Balian-Vénéroni variational principle is used to derive the time-dependent Hartree-Fock (TDHF) equation describing the dynamics at the mean-field level, as well as an extension including small-amplitude quantum fluctuations which is equivalent to the time-dependent random-phase approximation (TDRPA). Such formalisms as well as their practical implementation in the nuclear physics framework with modern three-dimensional codes are discussed. Recent applications to nuclear dynamics, from collective vibrations to heavy-ion collisions are presented. Particular attention is devoted to the interplay between collective motions and internal degrees of freedom. For instance, the harmonic nature of collective vibrations is questioned. Nuclei are also known to exhibit superfluidity due to pairing residual interaction. Extensions of the theoretical approach to study such pairing vibrations are now available. Large amplitude collective motions are investigated in the framework of heavy-ion collisions leading, for instance, to the formation of a compound system. How fusion is affected by the internal structure of the collision partners, such as their deformation, is discussed. Other mechanisms in competition with fusion, and responsible for the formation of fragments which differ from the entrance channel (transfer reactions, deep-inelastic collisions, and quasi-fission) are investigated. Finally, studies of actinide collisions forming, during very short times of few zeptoseconds, the heaviest nuclear systems available on Earth, are presented.     

Jacobi no-core shell model for p-shell hypernuclei

The European Physical Journal A - The ternary cluster decay of heavy nuclei has been observed in several experiments with binary coincidences between two fragments using detector telescopes (the...     

Baryon decays and gamma-spectroscopy of hypernuclei

The applicability of (K ^–,^–) - and (K ^–,^– N)-reactions on^13,14C and^14,15N nuclei to the study of -transitions in primary and daughter -hypernuclei is discussed. The intensity of -deexcitation of ¹³C state |S ¹²C(15·11 MeV; 1⁺1): 1/2⁺ has been shown to be comparable with the intensity of baryon decay. Isospin selection rules are used to distinguish excitation energy ranges of primary hypernuclei, where the identification of the secondary -lines is probable.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Nuclear magnetic relaxation and dynamics of biopolymers

A model is proposed in which the NMR relaxation dispersion profiles of biomolecule water solutions are interpreted in terms of magnetic field fluctuations due to the backbone vibrations involving the biopolymer paramagnetic nuclei. This model, which takes into account the experimental evidence which has appeared in the literature for a “fractal-like” density of vibrational state for the protein backbone, has been used to fit some experimental NMR relaxation profiles of biomolecule water solutions. The results obtained are discussed critically in connection with the data reported in the related literature.