Hyperfine switching triggered by resonant tunneling for the detection of a single nuclear spin qubit

A novel detection mechanism and a robust control of a single nuclear spin-flip by hyperfine interactions between the nuclear spin and tunneling electron spin are proposed on the basis of ab initio non-equilibrium Green's function calculations. The calculated relaxation times of the nuclear spin of proton in a nano-contact system, Pd(electrode)-H₂-Pd(electrode), show that ON/OFF switching of hyperfine interactions is effectively triggered by resonant tunneling mediated through the d-orbitals of Pd. The relaxation times at ON-resonance are ∼¹⁰³ times faster than those at OFF-resonance, indicating that ON-resonance is suitable for the detection (read-out) of nuclear spin states. In addition, the effectiveness of bias voltage applications at OFF-resonance for selective operations on the proton qubit is demonstrated in the calculations of the resonant frequencies of proton using the gauge-invariant atomic orbital method.     

The inhomogeneous Schrödinger equation for the off-shell wave function

A method has been developed for calculating the off-shell wave function by solving the inhomogeneous Schrödinger equation with allowance for the nuclear and Coulomb interactions. The off-shell wave function makes it possible to construct the off-shell scattering amplitude in order to solve the problems for three or more particles. An important application of the method is the Trojan Horse calculations of nuclear reactions that are important in nuclear astrophysics. Specific calculations are performed for neutron and proton scattering on the ⁷Be nucleus. The Woods-Saxon potential is used and the spin-orbital interaction is taken into account.     

The stability of cones and pyramids on sputtered surfaces of copper

A new modification of an earlier published model for the calculation of energy spectra of primary knocked atoms formed in the material under neutron, proton or other particle irradiation is being considered in the present paper. The new approach takes into account the angular momenta of interacting particles within the limits of the compound nucleus model. It is found that the model allows to carry out more accurate estimation of the quantities of nuclear reaction products. It also modifies the shape of the PKA energy spectrum. Control calculations for the nuclear reactions caused in proton irradiated copper have been made. The results of these calculations are in good agreement with the excitation functions for the nuclear reactions.     

Proton radioactivity with a Yukawa effective interaction

The half-lives of proton radioactivity of proton emitters are investigated theoretically. Proton-nucleus interaction potentials are obtained by folding the densities of the daughter nuclei with a finite-range effective nucleon-nucleon interaction having Yukawa form. The Wood-Saxon density distributions for the nuclei used in calculating the nuclear as well as the Coulomb interaction potentials are predictions of the interaction. The quantum mechanical tunneling probability is calculated within the WKB framework. These calculations provide reasonable estimates for the observed proton radioactivity lifetimes. The effects of neutron-proton effective mass splitting in neutron-rich asymmetric matter as well as the nuclear matter incompressibility on the decay probability are investigated.     

T-REX

The potential barrier impeding the spontaneous emission of protons in the proton radioactive nuclei is calculated as the sum of nuclear, Coulomb and centrifugal contributions. The nuclear part of the proton-nucleus interaction potential is obtained in the energy density formalism using the Skyrme effective interaction that results into a simple algebraic expression. The half-lives of the proton emitters are calculated for the different Skyrme sets within the improved WKB framework. The results are found to be in reasonable agreement with the earlier results obtained for more complicated calculations involving finite-range interactions.     

Nuclear interface energy at finite temperatures

The thermodynamic properties at finite temperatures of the plane interface between two phases of nuclear matter in equilibrium are examined theoretically, and explored numerically. The microscopic hamiltonian, the Skyrme I′ interaction, is used in the Thomas-Fermi approximation to obtain the finite-temperature extensions of earlier zero-temperature results which used the Hartree-Fock and Thomas-Fermi methods. Approximate analytic fits are given to the χ_i (proton fraction on the dense-matter side) dependence of the critical temperature, and to the T and χ_i dependences of the surface thermodynamic potentials, the density of surface neutrons, the surface entropy and the neutron and proton chemical potentials at phase equilibrium. These fits are an ingredient in a compressible liquid-drop nuclear model, the basis of an equation of state for hot, dense matter needed in certain astrophysical applications.The liquid-drop model is used here to construct an isolated, low-T nucleus, whose properties are compared with the original zero-T Hartree-Fock calculations which lead to the Skyrme I interaction, and with other mass formulae. The low-temperature expansion of the surface energy is compared with that obtained in other calculations. The nuclear level density at the Fermi surface, related to the low-T expansion of the entropy of the whole nucleus, is also discussed.     

The need for a state dependent interaction in proton inelastic scattering from 24Mg

The calculated angular distributions for proton elastic and inelastic scattering can be greatly improved by using an imaginary potential which depends upon the nuclear state. We demonstrate that this is just the effect expected from the coupling of deuteron channels and the phenomenon therefore provides a signature for multistep processes which is not dependent on detailed calculations. The obvious application to the usual DWBA calculations of inelastic proton scattering is mentioned.     

Short range correlations between nucleons in finite nuclei

The short-range correlation between nucleons in finite nuclei is investigated in high energy protonnucleus and α-nucleus elastic scattering in the framework of Glauber multiple scattering theory without any free parameters. The effects on the p-4He and 4He-12C elastic scattering, and in particular on the proton elastic scattering off hallo-like nuclei, 6,8He, are estimated. Our calculations show that the short-range correlations play an important role in reproducing experimental data and could be also thought of as being possible origin and nature of halo-like phenomena in the nuclear structure. More accurate calculations along this line are needed.     

Nucleon elastic scattering from 40Ca between 11 and 48 MeV

Differential cross sections for the elastic scattering of neutrons from ⁴⁰Ca have been measured in the 19–26 MeV region. The neutron elastic scattering data, previous neutron measurements and additional proton elastic scattering data are analyzed using three different approaches to the optical model potential: Woods-Saxon parameterization, model independent analysis and microscopic calculations. The difference between the phenomenological neutron and proton real potentials is studied in terms of Coulomb effects, nuclear polarization and charge symmetry breaking in the nuclear mean field.     

Nuclear Short range correlations in finite nuclei

The short-range correlations between nucleons in finite nuclei are investigated in the framework of Glauber multiple scattering theory without any free parameters. The effects on proton-nucleus and nucleus - nucleus interactions such as p - {4}He$ and {4}He- {12}C elastic scattering, and in particular the proton elastic scattering off hallo-like nuclei, {6,8}He, are estimated. Our calculations show that the short-range correlations play an important role in reproducing experimental data and could be also thought of as being the origin and nature of halo-like phenomena in the nuclear structure. More accurate calculations along this line are needed.     

Proton radioactivity — spherical and deformed

The proton drip line defines one of the fundamental limits to nuclear stability. Nuclei lying beyond this line are energetically unbound to the emission of a constituent proton from their ground states. For near-spherical nuclei in the region of the drip line between Z=69 (Tm) and Z=81 (T1), proton decay transition rates have been shown to be well reproduced by WKB calculations using spectroscopic factors derived from a low-seniority shell model calculation [2]. Another approach using spectroscopic factors obtained from the independent quasiparticle approximation has also proved successful in this region [3]. These interpretations have allowed the extraction of nuclear structure information from nuclei well beyond the proton drip line.     

利用GEANT4和FLUKA研究质子诱发散裂反应出射中子双微分截面

在中高能质子诱发散裂反应相关核工程设计中,可靠的蒙特卡罗模拟程序结合核反应理论模型具有较好的理论指导意义。本工作中,利用GEANT4耦合INCL4和ABLA理论模型以及FLUKA耦合PEANUT模型模拟计算了几百MeV至几个GeV质子轰击Be,Al,Fe,W,U等靶后30°,60°,120°,150°出射角产生的散裂中子双微分截面,并与现有实验数据进行了比较。结果发现,FLUKA和GEANT4模拟计算较好地再现了Al,Fe,W,U等靶实验测量数据。然而,模拟结果明显低估了Be靶出射中子能量小于10 MeV能区的实验数据。For the design of nuclear engineering related with medium-high energy proton induced spallation reaction,the reliable Monte Carlo simulation codes coupled with nuclear reaction models have a good theoretical guidance.In this work,the production spallation neutron double differential cross sections at 30°,60°,120°,150°emission angle for Be,Al,Fe,W,U target materials at incident proton energies between several hundred MeV and GeV are theoretically calculated by using the GEANT4 coupled INCL4 and ABLA,and the FLUKA coupled PEANUT.The calculated results were compared with the available experimental data.It is found that the GEANT4 and FLUKA calculations well reproduced the experimental measurement of Al,Fe,W,U target materials.However,calculations obviously underestimated the emission neutrons of Be target for lower than 10 MeV energy range.     

Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter based on improved approximation schemes

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the proton-neutron mass splitting in a more consistent way. The proton properties are particularly sensitive to this adaption and its consequences, whereas the neutron properties remains almost unaffected in neutron-rich matter. Although at present full Brueckner calculations are still too complex to apply to finite nuclei, these relativistic Brueckner results can be used as a guidance to construct a density-dependent relativistic mean-field theory, which can be applied to finite nuclei. It is found that an accurate reproduction of the Dirac-Brueckner-Hartree-Fock equation of state requires a renormalization of these coupling functions.     

与散裂中子靶物理相关的理论计算程序探讨I薄靶计算

利用中能强流质子加速器形成的散裂中子源作为外加中子源驱动次临界反应堆的洁净核能系统是目前国际上的一个研究热点 .散裂中子源是这个系统的一个重要部分 ,也是一个急需解决的重点.有关散裂靶物理的理论计算程序的建立和基准检验是目前工作的一个重点.The research for intermediate energy proton accelerator driven radiologically clean nuclear power system has attracted considerable attention. The spallation neutron source induced by intermediate energy proton nucleus interaction is a key point and has not solved yet for the transmutation and applications. The theoretical programs related to the spallation neutron source for accelerator driven system (ADS) are discussed at present work.     

Surface and curvature properties of neutron-rich nuclei

We use the extended Thomas-Fermi approximation and Skyrme-type interactions to describe the energy density of a semi-infinite slab of neutron-rich nuclear matter at zero temperature. We allow for the existence of a drip phase at low proton fractions in addition to the more dense nuclear phase. We determine various bulk properties of both phases when the system is in equilibrium. We extend the usual definition of the surface energy to apply to the case where drip is present. Assuming the density profile has the form of a Fermi function to a power, we perform a constrained variational calculation to determine the parameters of the density profile. The surface and curvature energies are calculated for proton fractions ranging from 0.5 (symmetric nuclear matter) to 0 (pure neutron matter) for typical Skyrme-type interactions. We find significantly different asymmetry dependences for different interactions. For proton fractions close to 0.5, our results are in close agreement with the predictions of the droplet model. We also present results of calculations for fission barrier properties and phase transitions between nuclei and bubbles to highlight the role of surface and curvature energies in the neutron-rich regime.     

Microscopic three-body force for asymmetric nuclear matter

Brueckner calculations including a microscopic three-body force have been extended to isospin-asymmetric nuclear matter. The effects of the three-body force on the equation of state and on the single-particle properties of nuclear matter are discussed with a view to possible applications in nuclear physics and astrophysics. It is shown that, even in the presence of the three-body force, the empirical parabolic law of the energy per nucleon vs. isospin asymmetry β = (N - Z)/A is fulfilled in the whole asymmetry range 0≤β≤1 up to high densities. The three-body force provides a strong enhancement of the symmetry energy which increases with density in good agreement with the predictions of relativistic approaches. The Lane's assumption that proton and neutron mean fields linearly vary vs. the isospin parameter is violated at high density due to the three-body force, while the momentum dependence of the mean fields turns out to be only weakly affected. Consequently, a linear isospin split of the neutron and proton effective masses is found for both cases with and without the three-body force. The isospin effects on multifragmentation events and collective flows in heavy-ion collisions are briefly discussed along with the conditions for direct URCA processes to occur in the neutron star cooling. Received: 18 February 2002 / Accepted: 16 May 2002     

质子化学位移各向异性的测量

测量质子化学位移各向异性（CSA）有助于表征分子结构与其动力学,但由于¹H-¹H同核偶极耦合相互作用很强及质子各向异性化学位移较小,测量质子化学位移各向异性仍具有巨大挑战,特别是对含有多种质子的生物大分子,如蛋白质.本文简要综述了测量质子化学位移各向异性的方法,包括同核去耦慢速魔角旋转方法、超快魔角旋转方法、对称重耦（RN_n^v）方法、xCSA方法以及量子化学计算方法.我们重点介绍了在高速魔角旋转条件下蛋白质氨基质子化学位移各向异性的测量及它们与氢键长度、蛋白质二级结构之间的关系.     

Skyrme Forces and Their Applications in Low Energy Nuclear Physics

This paper reviews the present status of Skyrme forces and their applications in the field of low energy nuclear physics as an effective nucleon-nucleon interaction. Their applications in the following five domains are presented:1). Hartree-Fock (HF), selfconsistent semiclassical (SCSC) calculations and nuclear ground state properties;2). random phase approximation (RPA), sum rule approach and properties of nuclear giant resonances;3). calculations of microscopic nucleon-nucleus optical potentials and related quantities;4). calculations of nucleus-nucleus optical potentials and fusion barriers;5). multifragmentation, liquid-gas phase transition and instability of hot/compressed nuclei.