实验核物理进展

本文回顾我所实验核物理科研人员在低能核反应机制、中子物理、核衰变性质及核结构研究中所做一系列工作,同时简单介绍了目前工作和设想． The paper reviews the research activities at SINR on experimental nuclear physics. The studies have been focused on mechanism of nuclear reactions, neutron physics,properties of nuclear decay and nuclear structure. Brief introductions are given to the ongoing research projects and future plans in the field of research.     

正电子寿命-动量关联技术

评述了国际正电子领域的新探测技术———寿命 动量关联技术.介绍了该技术的发展过程,讨论了该技术的分析方法,详细阐述了该技术在Ps形成和热化过程中的应用,并讨论了该技术在Ps化学上的应用.A new detection technique--age momentum correlation in international positron field is reviewed. The recent development is described and the analysis methods are discussed for the technique. The application of the technique in the positronium formation and thermalization processes are systematically summarized. Besides the application of the technique in Ps chemistry is discussed.     

小波分析及神经网络方法在核物理及核工程中的应用

介绍了小波分析和神经网络方法在核物理及核工程领域的应用现状。 分别对小波分析及神经网络方法的基本原理进行了介绍, 详细讨论了小波变换中的多分辨分析方法在γ能谱平滑以及核电站设备监测等方面的应用, 讨论了连续小波变换在γ能谱分析、 粒子种类鉴别以及核反应堆安全监测等领域的应用。 同时, 还详细介绍了神经网络方法在以上各领域的发展现状。 最后, 展望了两种方法在核安全检测、 核辐射防护以及核电站实时监控等领域的发展趋势。 Applications of wavelet analysis and neutral networks in the field of nuclear physics and engineering are reviewed. The principle of these two methods are introduced briefly, and then the applications of multiresolution analysis technique in the smoothing of γ ray spectroscopy, and in nuclear power plant monitoring are discussed in detail. Applications of the continuous wavelet analysis method in γ ray spectroscopy analysis, in particle identification , and in nuclear reactor safety monitoring are also talked over. In addition, the applications of neutral networks in above fields are introduced. Finally, the trends of the future development for these two methods are prospected.     

Laser output of radial-slab solid-state laser

In this letter, numerical simulation and experimental study of a radial-slab solid-state laser are presented. The laser includes four crossing-slabs pumped by four Xe flashlamps. The numerical simulation of coherent intensity in the near field and the far field indicates that the laser with the structure can improve the quality of output beam compared with incoherent beam combination. The radial-slab solid-state laser is fabricated, and initial experiments are carried out at a pulse repetition of 1 Hz. Nine beams in the near field and one combined beam in the far field are obtained in our initial experiment. The experimental results are consistent with the numerical analysis in the coherent condition. The results show that coherent beam combination is obtained by this laser.     

Study of the surface and far fields of terahertz radiation generated by large-aperture photoconductive antennas

We have studied analytically the temporal characteristics of terahertz radiation emitted from a biased largeaperture photoconductive antenna triggered by an ultrashort optical pulse. We have included the effects of the finite lifetime and transient mobility dynamics of photogenerated carriers in the analysis. Succinct explicit expressions are obtained for the emitted radiation in the surface field and in the far field. The dependence of the waveforms of the radiated field on the fluence and duration of triggering optical pulse, carrier relaxation time and carrier lifetime are discussed in detail using the obtained expressions.     

Investigation of electric fields inside and outside a magnetised cold plasma sphere

Based on the scales transformation of electromagnetic theory,the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic parameter.The obtained results are in good agreement with that in the literature.The angle between the direction of inside field and that of outside field is derived.In S wave band,calculations for the effects induced by parameters of the inner field are established.Simulations show that the angle between incident field and the outside magnetic field influences the inner field remarkably.The inner field will increase as the electron density increases.The inner field varies with frequency nonlinearly.There is an angle between the inner field and the incident field,it changes nonlinearly with the frequency.     

Binding Energies of Excitons in Square Quantum-Well Wires in the Presence of a Magnetic Field

The binding energies of the ground state of excitons in the GaAs/Ga1-xAlxAs square quantum-well wire in the presence of a magnetic field are investigated by using the variational method. It is assumed that the magnetic field is applied parallel to the axis of the wire. The calculations of the binding energy as a fimction of the wire size have been performed for infinite and finite confinement potentials. The contribution of the magnetic field makes the binding energy larger obviously, particularly for the wide wire, and the magnetic field is much more pronounced for the binding energy in a square quantum wire than that in a cylindrical quantum wire. The mismatch of effective masses between the well and the barrier is also considered in the calculation.     

Coupling of Acoustical Plane p-Wave to a Cased Borehole

Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot＇s theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively. The resonant characteristics of the scattering field are also analyzed from the physical sense.     

Positron-impact ionisation of atomic hydrogen in the presence of a bichromatic laser field

The positron impact-ionisation of atomic hydrogen in the presence of a linearly polarised bichromatic field is investigated in the first Born approximation.The field is composed of a fundamental frequency and its second harmonic.The state of positron in the field is described by the Volkov wavefunction,and the continuum state of the ejected electron is described by the Coulomb-Volkov wavefunction.The dressed ground state of target is a first order time-dependent perturbative wavefunction.The triple differential cross sections and their dependencies on laser field parameters are discussed and compared with the results modified by a monochromatic field.Numerical results show that the coherent phase control is significant and the laser-assisted ionisation cross sections caused by positron and electron are different.     

Full-vectorial analysis of optical waveguides by the finite difference method based on polynomial interpolation

Based on the polynomial interpolation, a new finite difference (FD) method in solving the full-vectorial guided-modes for step-index optical waveguides is proposed. The discontinuities of the normal components of the electric field across abrupt dielectric interfaces are considered in the absence of the limitations of scalar and semivectorial approximation, and the present FD scheme can be applied to both uniform and non-uniform mesh grids. The modal propagation constants and field distributions for buried rectangular waveguides and optical rib waveguides are presented. The hybrid nature of the vectorial modes is demonstrated and the singular behaviours of the minor field components in the corners are observed. Moreover, solutions are in good agreement with those published early, which tests the validity of the present approach.     

不同规范下横场与纵场的特性分析

文章按照矢量场分解为横场和纵场的方法,采用亥姆霍兹定理,研究电磁场的性质与结构.对不同规范下电磁场的横场和纵场特性进行分析与比较,讨论电磁场与源之间的对应关系.结果表明,电磁场问题由电荷场和电磁波动场两个相互独立的问题组成,远区辐射场由横场部分决定,纵场部分并不辐射出去;电磁势函数存在过多自由度可以归因于纵场分量的不唯一性,标量势所满足的方程并不独立于各自对应的矢量势所满足的方程.     

平面横电磁波模的初值问题

经典理论所描述的电场和磁场处处同相的平面电磁波模并不存在.Maxwell方程组的解依赖于 电磁场的初始值或边界条件,根据不同的初始条件解得的平面电磁波模是不同的.结果表明 ,平面电磁波是横波,在不同的位置,由变化的电场激发的磁场或由变化的磁场激发的电场 振幅不同,电场与磁场的相位差也不同. 关键词： Maxwell方程组 最优微分方程 初始条件 平面电磁波     

失谐量对多模场非简并多光子Jaynes-Cummings模型量子场熵演化的影响

利用Von Neumann约化熵理论研究了多模相干态场与二能级原子非简并多光子相互作用系统中量子场熵的时间演化特性,得到了含有失谐量的多模场熵的解析表达式,并通过数值计算讨论了光场为三模场时频率失谐量对场熵演化的影响.结果发现：当近共振时,失谐量几乎不影响场与原子之间的纠缠特性;而当远离共振时,量子场熵很强地依赖于失谐量的大小,特别是当失谐量足够大时,场与原子几乎总是处于纠缠态.     

Calculation of critical states of superconducting multilayers based on numerical solution of the Ginzburg-Landau equations for superconducting plates

Numerical methods are used to analyze the Ginzburg-Landau equations for a superconducting plate carrying transport current in a magnetic field. Critical current is calculated as a function of the applied magnetic field strength for superconducting plates with different thicknesses. The relations between the field dependence of critical current and the distributions of order parameter, magnetic field, and supercurrent in a plate are analyzed. The field-dependent critical currents computed for plates are used to determine the critical current as a function of the applied magnetic field strength and local magnetic field and current distributions for multilayers in parallel magnetic fields. The constituent superconducting layers are assumed to interact only via magnetic field. A simple method is proposed for analyzing the critical states of multilayers in magnetic fields of arbitrary strength, based on elementary transformations of the critical current-density distribution over individual layers in zero applied magnetic field. The method can be used to analyze experimental results.     

声诱导电磁场的赫兹矢量表示与多极声电测井模拟

在假设声场不受电磁场影响的前提下，将Pride声电耦合方程组化为具有电流源的麦克斯韦方程组.与空间位置固定的电流源产生的电磁场不同，孔隙地层中声波诱导的电磁场是由空间波动的电流源产生的.通过引入赫兹矢量，将求解麦克斯韦方程组问题转化为求解关于赫兹矢量的非齐次矢量赫姆霍兹方程组.通过求解该方程组，得出电磁场表达式.利用此方法，针对声电效应测井，分别计算了由单极声源、偶极声源、四极声源激发的井内声场及其诱导电磁场的全波波形. 关键词： 孔隙介质 诱导电磁场 测井 多极声源     

Properties of an adiabatically cooled SK spin glass

Some physical properties of an SK spin glass subject to slow cooling are investigated. Among those are Edwards-Anderson order parameter, energy, field cooled and zero field cooled susceptibilities. The results are compared with predictions from Parisi's solution. Different values are obtained for the field cooled susceptibility whereas other quantities are identical in both calculations. Ultrametricity results in a natural way if adiabatic temperature changes involving cooling and heating periods are considered. Some results are also given for adiabatic cooling in a finite external field and for adiabatic changes of the field at constant temperature. The present setup allows to investigate explicitly the dependence on history at least for adiabatic changes of temperature and external field.     

耦合双原子Jaynes-Cummings模型的腔场谱H

研究了处于激发态的两原子与高Q腔场相互作用单光子过程的腔场谱,给出了初始光场为光子数态、相干态、压缩真空态时的腔场谱数值计算结果,分析了原子间偶极-偶极相互作用强度gα对腔场谱结构的影响.发现真空场Rabi峰,当gα较弱时为4峰,gα较强时为3峰结构;弱场数态(n＞0)时为5峰,强场时为3峰结构.相干态和压缩真空态时,谱结构与光子数分布有关,一般为复杂的多峰结构.结果表明,gα对峰位峰高都有影响,破坏了谱结构的对称性,但这种影响只在真空场和弱场时才较明显.     

Interstellar Magnetic Fields

Methods of investigating interstellar magnetic fields in spiral galaxies are reviewed. Linearly polarized radio continuum emission yields information about strength and structure of the field. Data are available for our Galaxy and several nearby galaxies. The field strengths vary between 3 and 13 , ?G; a correlation with the average surface mass density of the galaxies is indicated. The field of M31 is probably concentrated in a ring-like torus, as predicted by the dynamo theory. The field structure of M33, however, appears to be bisymmetric as expected in the primordial theory of field origin. Other candidates for a bisymmetric field structure are M51, M81, M83, NGC 2903, and NGC 6946, but the observations are not yet conclusive. The magnetic field in IC 342 is too complicated to be described in terms of a simple model. The interaction processes between the field and the various components of interstellar gas should be investigated in more detail.     

Rapid magnetization reversal in magnetic small particles induced by non-static bias field

Magnetization reversal processes by a switching field in single-domain nano-sized magnetic particles in the presence of a small transverse non-static bias field are studied. Applying an oscillating bias field instead of a static field, the reversal time becomes much shorter when the switching field is slightly stronger than the effective anisotropy field. A pulsed bias field of a suitably chosen duration in the nanosecond scale is found to induce a rapid switching, even when the switching field is smaller than the anisotropy field. The dependence of the reversal time on the frequency of an oscillating bias field and the duration of a pulsed bias field are studied. The present work thus complement the earlier studies on switching in the presence of a static bias field.