奇异核的实验研究

总结了兰州放射性束实验小组在兰州放射性次级束流线上近几年来利用产生的放射性束流,轰击Si或C等靶子,测量它的反应总截面.并利用经验公式将这些结果归一到相同的能量和靶子,与其相邻的核相比较,发现了⁹C,¹¹Be,¹⁴Be,⁸B,¹⁴B 和¹²N等核素的反应总截面值有奇异增大的现象.利用微观的Glauber模型进行了计算,对有奇异结构的核采用核芯加价核子的密度分布形式,理论计算和实验结果符合得很好,可以给出奇异核的弥散的密度分布.     

22Na放射源慢正电子束流插入装置的研制

北京慢正电子强束流是利用北京正负电子对撞机电子直线加速器电子打靶产生的高强度低能单色正电子束流. 为了提高强束流的机时利用效率和节省强束流用于新建实验站的调试机时, 设计了一套基于²²Na放射源的慢正电子束流装置插入到强束流输运线上. ²²Na放射源慢正电子束流插入装置主要包括²²Na放射源及慢化体、E×B能量选择器、多级静电加速管、磁场输运系统、真空系统、高压绝缘和辐射防护措施等.     

22Na(p,γ)23Mg反应的实验研究

讨论了目前有关²²Na(p,γ)²³Mg反应的实验研究工作,结合兰州放射性束流线上的放射性束流²³Al的β⁺延发质子衰变实验的测量结果,给出了²³Al延发衰变的质子能谱,并比较了近期实验给出的相关能级的自旋、宇称值,正是由于这种自旋、宇称和能级部分宽度的不确定性,导致了反应率计算的不确定性.计算了同位旋相似态的共振强度.对于测量到的新的延发衰变能级E_d=8.916MeV,由于没有相应的能级宽度值,实验仅给出其相对共振强度值.     

40Ca+58Fe,58Ni反应中的径向膨胀流研究

利用同位旋相关的Boltzmann-Langevin方程研究了⁴⁰Ca+⁵⁸Fe和⁴⁰Ca+⁵⁸Ni两个反应系统在53,100,150和200MeV/u入射能量下对心碰撞的径向膨胀流.发现对于丰中子系统⁴⁰Ca+⁵⁸Fe的径向膨胀流系统性地小于稳定系统⁴⁰Ca+⁵⁸Ni的径向膨胀流.在假定轰击能量与反应体系的压缩密度呈抛物线关系时,能够解释入射能量和径向膨胀流之间呈现的直线关系.提取了出现径向膨胀流的轰击能量阈值,发现对丰中子系统⁴⁰Ca+⁵⁸Fe得到的能量阈值小于稳定系统⁴⁰Ca+⁵⁸Ni所得到的能量阈值.     

径向膨胀流的同位旋效应

利用同位旋相关的量子分子动力学模型,研究了¹²⁴Ba+¹²⁴Ba和¹²⁴Sn+¹²⁴Sn两个系统在不同入射能量下对心碰撞的径向膨胀流.发现丰中子系统¹²⁴Sn+¹²⁴Sn的径向膨胀流系统性地小于系统¹²⁴Ba+¹²⁴Ba的径向膨胀流.同时发现这种差别主要来自于核子–核子碰撞截面的同位旋相关性而几乎与对称能无关.     

中能重离子碰撞中集体流的同位旋效应

在同位旋相关的量子分子动力学模型的基础上,利用Skyrme–Hartree–Fock计算所得的中子、质子密度,同时利用费米气体模型得到相应的中子、质子费米面,抽样出稳定的⁵⁸Fe和⁵⁸Ni初始核.仔细研究了55MeV/u ⁵⁸Fe+⁵⁸Fe和55MeV/u⁵⁸Ni+⁵⁸Ni两个反应中集体流的同位旋效应.在不同碰撞参数下对不同类型的碎块,观察到丰中子反应系统⁵⁸Fe+⁵⁸Fe比⁵⁸Ni+⁵⁸Ni有更强的集体流,并能与实验结果定性符合.同时,研究了同位旋相关的对称能与核子–核子碰撞截面对集体流的影响.     

Bd0→φK0极化反常和Bd→φKS CP不对称的研究

在模型Ⅲ下, 仅考虑来自于中性规范玻色子H⁰, h⁰和 A⁰产生的树图阶味改变中性流的贡献, 并利用QCD因子化方法, 对B_d⁰→φK^*0衰变过程的极化反常和 B_d→φK_S衰变过程的CP不对称进行了研究, 经过计算发现, 在147<|λ_bsλ_ss|<165的参数范围内, 这两个过程中存在的反常现象能够同时给予解释.     

RIBLL束流诊断

描述了兰州放射性离子次级束流线(RIBLL)上研制并安装使用的放射性束流(RIB)诊断装置的种类、结构、性能及在AIBLL上的位置和功能.重点叙述了以光纤为基础的几种诊断元件,它们探测效率高、响应时间快、制作容易、性能稳定.给出了RIB¹⁷N等高图,说明诊断装置辅助MBLL得到RIB的水平.     

同位旋非对称核物质性质与扩展的BHF方法(Ⅶ)中子星物质中质子和中子的1S0态超流性

利用Brueckner Hartree Fock和BCS理论方法,计算了β稳定中子星物质中处于¹S₀ 态的质子和中子的对关联能隙,着重研究和讨论了三体核力的影响.结果表明三体核力对β稳定中子星物质中¹S₀态中子超流性的影响相对较小,但对¹S₀态质子超流性具有重要影响,而且其效应随核子数密度增大而迅速增强.三体核力的主要作用是强烈地抑制了高密度β稳定中子星物质中的1S0态质子超流性.     

相对论重离子碰撞中的K+产生及集体流

用自洽的相对论BUU模型研究了相对论重离子碰撞的K⁺产生及流,研究结果表明K⁺集体流在相对论重离子碰撞中对核态方程(EOS)和K–N标量吸引项(∑_KN)是敏感的,在对K⁺流中心度依赖的研究中发现在大碰撞参数时有反向流出现,可为确定∑_KN值提供更为有效的信息.对K⁺产生的总产额及各个不同道的贡献与EOS和∑_KN关系进行了细致分析,表明N△道对K⁺产生的贡献和影响都是最显著的; 不同道的贡献对∑_KN的灵敏程度不同,其中∑_KN对N△道的影响要比对πB道的大.     

Flaw location errors in extruded stainless steel piping

Refracted shear waves in extruded stainless steel pipes were found to change their velocity and direction (beam skewing) as they propagated through the pipe thickness. These variations in refracted angles and velocities result in flaw location errors during ultrasonic examination. Two techniques, one using refracted shear waves in pitch-catch mode and the other refracted longitudinal waves in pulse-echo mode, are discussed as to their feasibility in determining the flaw location accurately in these pipes. The result of the work was that a two-scan approach using refracted shear waves in pulse-echo for flaw detection and refracted longitudinal waves in pulse-echo for flaw location was recommended.     

Propagation properties of partially polarized Gaussian Schell-model beams through an axis-unsymmetric paraxial ABCD system

By using the beam coherence-polarization (BCP) matrix approach, analytical propagation equations of partially polarized Gaussian Schell-model (PGSM) beams through an axis-unsymmetric paraxial optical ABCD system are derived, which enable us to study the propagation-induced polarization changes and irradiance distributions at any propagation distance of PGSM beams through axis-unsymmetric systems within the framework of the paraxial approximation. Detailed numerical results for a PGSM beam passing through a bifocal lens are presented to illustrate the propagation properties of PGSM beams. A comparison with the previous work is also made.     

Propagation of the radiation field excited on discontinuities of optical waveguides

Numerical and semi-analytical techniques widely used to model the complicated structure of the radiation field excited on sharp and smooth discontinuities of a dielectric slab are reviewed. Comparative analysis of the radiation field modelling by the fast Fourier transformation-beam propagation method (FFT-BPM) and the finite difference (FD)-BPM is presented. Propagation of a higher-order mode through the cut-off cross-section of smooth and sharp discontinuities is simulated numerically by the FD-BPM, the total field is analysed using the leaky mode approach.     

Real-time detection of focal position of workpiece surface during laser processing using diffractive beam samplers

The real-time fabrication of microgrooves on a curved surface using a laser beam, without preprogramming their shapes into the machining instructions, is a major challenge in laser processing owing to limitations associated with the real-time detection of the focal position. A new approach using a sampled fraction of the beam from a diffractive beam sampler (DBS) is therefore presented in order to overcome this limitation. By considering the sampled fraction of the beam an analysis of the results allows for precise positioning of the specimen for focal-point identification. This allows for the determination of the focus for a broad variety of laser types and laser powers, thereby providing stringent focusing conditions with high numerical apertures. This approach is easy to implement, inexpensive, independent of the roughness or granularity of the workpieces, and more importantly does not require auxiliary lasers and displacement sensors for real-time measurement during the fabrication process.     

Scatter correction for cone-beam computed tomography using self-adaptive scatter kernel superposition

The authors propose a combined scatter reduction and correction method to improve image quality in cone beam computed tomography (CBCT). The scatter kernel superposition (SKS) method has been used occasionally in previous studies. However, this method differs in that a scatter detecting blocker (SDB) was used between the X-ray source and the tested object to model the self-adaptive scatter kernel. This study first evaluates the scatter kernel parameters using the SDB, and then isolates the scatter distribution based on the SKS. The quality of image can be improved by removing the scatter distribution. The results show that the method can effectively reduce the scatter artifacts, and increase the image quality. Our approach increases the image contrast and reduces the magnitude of cupping. The accuracy of the SKS technique can be significantly improved in our method by using a self-adaptive scatter kernel. This method is computationally efficient, easy to implement, and provides scatter correction using a single scan acquisition.     

Propagation of the radiation field excited on discontinuities of optical waveguides

Numerical and semi-analytical techniques widely used to model the complicated structure of the radiation field excited on sharp and smooth discontinuities of a dielectric slab are reviewed. Comparative analysis of the radiation field modelling by the fast Fourier transformation-beam propagation method (FFT-BPM) and the finite difference(FD)-BPM is presented. Propagation of a higher-order mode through the cut-off cross-section of smooth and sharp discontinuities is simulated numerically by the FD-BPM, the total field is analysed using the leaky mode approach.     

Focusing of a singular beam in the presence of spherical aberration and defocusing

Focusing of a singular beam by a lens in the presence of spherical aberration and defocusing is studied by using Fresnel–Kirchhoff diffraction integral for two different values of topological charge. Results of intensity distribution and encircled energy are plotted for defocused observation planes. Spherical aberration spreads the dark core and reduces the intensity at maxima. The results have been verified by the optical transfer function (OTF) approach.     

利用共振辐射压力获得准单一速度原子束

报道了利用行波场的共振辐射压力获得准单一速度原子束的实验研究结果，并进行了理论分析。实验上利用斜入射失谐为－１００ＭＨｚ行波光场共振作用原子束可使准单一速度原子束偏转１．７ｍｍ，速度宽度小于５８ｍ／ｓ。     

Multi-objective optimisation of laser beam cutting process

This paper presents a hybrid Taguchi method and response surface method (TMRSM) for the multi-response optimisation of a laser beam cutting process. The approach first uses the Taguchi quality loss function to find the optimum level of input cutting parameters such as assist gas pressure, pulse width, pulse frequency and cutting speed. The optimum input parameter values are further used as the central values in the response surface method to develop and optimise the second-order response model. The two quality characteristics Kerf width (KW), and material removal rate (MRR), that are of different nature (KW is of the smaller-the-better type, while MRR is of the higher the better type), have been selected for simultaneous optimisation. The results show considerable improvement in both the quality characteristics when the hybrid approach is used, as compared the results of a single approach.     

The aperture effect on the propagation of partially polarized Gaussian Schell-model beams

Based on the beam coherence-polarization (BCP) matrix approach and propagation law of partially coherent beams, the propagation of partially polarized Gaussian Schell-model (PGSM) beams through an aperture is studied. Numerical calculation results are given to illustrate the propagation-induced polarization changes and irradiance distribution of PGSM beams for the apertured case.