金属环境中低能D(d,p)T反应的研究

近年来一系列实验表明, 金属环境中的低能带电粒子引起的核反应截面与气体靶中的相比出现明显增大, 这种现象通常被归结为电子屏蔽效应。 全面介绍了金属环境中D(d, p)T反应电子屏蔽效应的测量方法、 数据分析和实验结果的规律性, 并简要论述了包括德拜等离子体模型在内的各种理论模型对实验结果的解释。 通过研究, 可以获得有关核物理、 核天体物理和凝聚态物理的宝贵知识。 The cross sections σ(E) of low energy nuclear reactions induced by charged particles in metallic environment are much larger than that in gas. Generally, it was taken as the effect of the electron screening. In this work, the experimental method of the D(d, p)T reaction in metallic environment was introduced. The data analysis and the regularity of experimental results were also discussed. All kinds of theoretical models including the Debye model were discussed, which can roughly explain the results of the experiments. The valuable knowledge of nuclear physics, nuclear astrophysics and condensed state physics can be obtained in the study of low energy nuclear reaction in metallic environment.     

厚靶低中能9Be(d,xn)反应加速器中子源特性研究

利用PHITS程序评价计算了厚靶9Be(d, xn)反应加速器中子源的能谱和角分布数据，重点讨论了JQMD、INCL和INCL/DWBA三种核反应物理模型计算厚靶9Be(d, xn)反应中子辐射场分布的适用性。研究结果显示，基于INCL/DWBA耦合模型的PHITS程序计算所得到的厚靶9Be(d, xn)反应中子能谱和角分布数据能够较好地与实验数据符合，可以为厚靶9Be(d, xn)反应中子源特性研究及应用提供较为准确的中子辐射场数据。此外，设计了水冷大面积旋转铍靶的方案，并在5~25 MeV/5 mA入射氘能量下条件下，开展了靶面温度模拟研究，结果显示，靶面最高温度可控制在100 oC以下。     

应用SVRT模型对氢与氘代甲烷反应的四维量子散射计算

应用SVRT(Semirigid Vibrating Rotor Target)模型和含时波包法对H CD4→HD CD3反应体系进行了量子散射计算,得出了该体系基态的反应几率,散射截面和热速率常数等量子结果,并比较了靶分子氘代甲烷中氘对氢的替代效应。     

氘化对KH2PO4晶体微观缺陷影响的正电子湮没研究

采用传统降温法从不同程度氘化(x=0, 0.51, 0.85)的生长溶液中生长氘化KH₂PO₄(KDP) 晶体, 利用正电子湮没技术(正电子寿命谱和多普勒展宽谱)、结合X射线衍射谱(XRD) 结构分析, 对KDP晶体氘化生长的微观缺陷进行了研究, 讨论了氘化程度对晶体内部微观结构特性、缺陷类型和浓度的影响. XRD结果显示晶胞参数a, b值随氘含量的增加而增加, c值无明显变化; 正电子寿命谱结果发现随着氘化浓度的提高, KDP晶体内部中性填隙缺陷以及氧缺陷不断增加, 引起晶体晶格畸变; 氢空位、K空位、杂质替位缺陷不断发生缔合反应形成复合缺陷, 缺陷浓度不断减少; 团簇、微空洞等大尺寸缺陷也在不断发生聚合反应, 缺陷浓度表现为不断减少. 多普勒实验结果表明随着氘化程度的提升, 晶体内部各类缺陷表现为同步变化. 实验结果表明, KDP晶体在低浓度氘化生长(50%以内)下缺陷反应较弱, 而在高浓度氘化(50%以上)下的缺陷反应显著增强.     

厚靶D（d,n）^3He反应加速器中子源的产额、能谱和角分布

给出一种计算氘钛厚靶D(d,n)3He反应加速器中子源的产额、能谱和角分布的方法,并发展了一个计算机模拟程序,程序能够计算氘束流能量小于1.0 MeV的中子源的产额、能谱和角分布.计算时使用推荐的D(d,n)3He反应截面数据和来自SRIM-2003程序的氘在氘钛靶中的阻止本领数据.给出一些典型计算结果,包括中子积分产额、中子能谱和角分布.     

电子垂直入射电离氦原子碰撞机理的理论研究

用3C模型和修正后的3C模型在低能、两个出射电子等能分享几何条件下,对电子垂直入射碰撞电离氦原子的三重微分散射截面进行了理论计算,并把计算结果与实验测量结果进行了比较,系统研究了(e,2e)反应中各种屏蔽效应对氦原子三重微分散射截面的影响,同时对截面中形成各峰的碰撞机理做了详细的探讨.研究结果表明:在入射能较低时,各种屏蔽效应对氦原子的三重微分散射截面幅度以及角分布均存在一定影响,并且形成各峰的碰撞机理直接影响截面的变化规律.     

利用时间分辨Ar的K壳层发射光谱诊断内爆靶丸芯区电子温度的时间演化过程

在神光Ⅱ装置上的内爆实验中,通过在充氘气(D2)的靶丸中掺入氩(Ar)元素,利用晶体谱仪配条纹相机测量得到了内爆停滞阶段Ar的K壳层发射光谱随时间的变化。在实验中,观测到Ar的Heα,Heβ以及Lyα线发射,持续时间大约200ps。用Heα线与Lyα线强度比值来推断靶丸芯区电子温度。利用碰撞辐射模型,从理论上计算出Heα线与Lyα线强度比值随电子温度、数密度的变化。通过将实验上观测到的Heα线与Lyα线强度比与理论计算值相比较,获得了芯区电子温度随时间的演化。并计算比较了不同电子密度条件下推断出来的电子温度的差异,证明诊断电子温度的方法对电子数密度的变化不敏感。利用逃逸因子修正了自吸收效应,从计算的结果可以看出在目前的实验中Heα线和Lyα线是光学薄的。     

氦原子(e,3-1e)反应中未探测电子屏蔽效应的理论研究

在DS3C模型的基础上,对氦原子(e,3-1e)反应的末态He+2场中未探测电子的屏蔽效应进行了研究.计算了(e,3-1e)过程中入射能为640 eV时,电子入射双电离He原子的四重微分截面(4DCS);讨论了非一级效应对截面结构的影响.所得结果与其他理论计算进行比较发现:文中结果与最新测量的实验数据较好地吻合.     

等离子体效应对碳的类氢离子能级的影响

通过在狄拉克方程中考虑德拜休克尔(Debye-Hückel)屏蔽势,研究了类氢离子C5 低能级能量1s(2S1/2),2s(2S1/2),2p(2P1/2和2P3/2)随等离子体电子温度及电子密度的变化规律,计算得到类氢离子C5 能级能量及能级电离势随等离子体环境的变化关系。同时,拟合得到了基于德拜休克尔屏蔽势下相当好的束缚态能级能量随等离子体环境变化的解析公式,利用该公式得到了类氢离子C5 相应各能级发生压致电离的临界电子密度,其结果与其它文献比有很好的可比性。结果表明:束缚态能级能量随等离子体电子温度的升高而减小,随等离子体电子密度的增大而增大。能级能量百分漂移量的对数值与等离子体电子密度的对数值以及等离子体电子温度的对数值之间均呈现出近似线性关系。对计算等离子体电离态分布及光谱模拟具有一定的意义。     

Mo(d,x)~(95m)Tc,Mo(d,x)~(96g),Tc和Mo(d,x)~(97)Tc反应的激发函数

用活化法和迭靶技术,测量了入射氘核能量从3.2到13.3MeV范围内,Mo(d,x)~(95m)Tc,Mo(d,x)~(96g)Tc和Mo(d,x)~(97m)Tc反应的激发函数,并与复合核统计模型理论计算作了比较。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.