(n,2n)反应同质异能态截面比

在统计理论及考虑角动量守恒的激子模型的基础上,运用Monte Carlo方法计算(n,20)反应同质异能态截面比. 以⁵⁹Co(n,2n)⁵⁸Co、⁹³Nb(n,2n)⁹²Nb和¹⁸¹Ta(n,2n)¹⁸⁰Ta的3个反应道为例,计算从其阈能到20MeV能区的同质异能态截面比,并和已有实验数据做了比较,结果符合较好. 这表明本文提供的方法是计算(n,2n)反应同质异能态截面比的一种有效方法.     

奇—奇核114Pm高自旋同质异能态及其衰变纲图的研究

用高自旋同质异能态次级束流线实验装置,对¹⁴⁴Pm的高自旋同质异能态进行了快速分离,并做了γ射线的符合测量.结合γ射线激发函数和各向异性的测量结果,首次建立了奇—奇核¹⁴⁴Pm的高自旋同质异能态的衰变纲图,其中19条高自旋能级和29条γ射线是由本工作指定的.离子γ射线关联测量确定了¹⁴⁴Pm的高自旋同质异能态的半衰期大于2μs.通过系统性比较以及变形的独立粒子模型理论计算,指定了高自旋同质异能态的粒子组态可能为π(1h²_11/2d_5/2)v(1i_13/21h_9/22f_7/2),自旋宇称为J^π=27⁺,并具有形变参数为β=－0.18的扁椭球形状.     

中子反应同质异能态截面比的系统学

提出了中子反应同质异能态截面比的半经验公式.该公式含有一系统学参数,适应于产物核质量数44≤A≤197、同质异能态自旋0≤J_m≤12和基态自旋0.5≤J_g≤8的中子反应.在入射中子能量E_n<20MeV能区,对该系统学参数进行了系统学研究.通过获得的半经验公式和系统学参数,可以很好地再现已有实验数据,也可较好地预言无实验数据的同质异能态截面比或同质异能态截面.     

40Ca和208Pb快中子辐射俘获过程研究

对快中子引起的核反应作预平衡修正,即考虑直接–半直接俘获作为统计平衡前1激子态和3激子态的γ发射过程,5个及5个以上激子态的粒子(中子、质子及α粒子等)及γ发射过程用达到统计平衡的复合核过程描述,在中子入射能量3MeV至20MeV能区对⁴⁰Ca和²⁰⁸Pb的辐射俘获截面进行了理论计算并与实验结果作了比较,得到了较好符合的结果.同时,对统计平衡前后γ发射对(n,γ)截面的贡献及直接俘获、半直接俘获和两者的相干项的特性进行了讨论     

恒星能量下核子俘获反应率的晕核效应

恒星能量下俘获截面很难直接测量。¹⁰Be（n，γ）¹¹Be俘获反应涉及到非均匀宇宙大爆炸核合成，无直接测量实验截面数据。利用转移反应¹⁰Be（d，p）¹¹Be的渐近归一化系数（ANC）方法，计算了¹⁰Be（n，γ）¹¹Be俘获反应截面和反应率。¹¹Be是中子晕核。研究表明，在恒星能量下俘获到晕态的截面和反应率显著增大。     

同质异能靶核的中子核反应计算

基于光学模型和带宽度涨落修正的Hauser-Feshbach理论编写了程序OMHFISO, 该程序适用于计算靶核处于同质异能态并且入射粒子能量小于5MeV的核反应, 入射粒子和出射粒子均可以是n,p,d,t,³He和⁴He 6种.迄今还很少有人计算过同质异能靶核的全套核数据.利用程序UNF, OMHFISO以及DWUCK4计算了不稳定同位素⁹⁰Rb和^{91,93,96,97,98}Y的同质异能靶核在入射粒子能量低于20.0MeV的全套中子反应数据, 并且得到了合理的结果.     

在轻核区核反应中的强非统计效应

本文研究²⁷Al(n,γ)和²⁸Si(n,γ)反应的非统计效应.考察的中子能量范围为热能至2MeV.所研究的非统计过程在低能区(热中子至第一共振前)包括位阱俘获、价俘获、以及两者的干涉;在高能区(共振区、研究对能量平均的截面)包括直接-半直接俘获,复弹性散射道及复非弹性散射道的俘获.计算结果表明,与中重质量核相比,这两个核的非统计效应在总的(n,γ)截面中所占的比例特别高:在热中子能量范围约为50%;在共振区区80%.本文指出,这一现象是与实验上观测到的关联系数相一致的.     

描述中子辐射俘获截面非统计效应的统一表象

基于对俘获态及终态波函数的自洽描述,建立了计算核子辐射俘获反应非统计效应的统一表象.应用这一模型对²⁷Al、⁵⁵Mn、⁸⁹Y和²⁰⁸Pb等四个核素在中子能量为0。1—20MeV能区计算了中子辐射俘获截面,并与实验值进行了比较.     

近垒及垒下12C+93Nb的蒸发剩余核截面

使用离线γ测量技术在实验室系28.3MeV至45.7MeV的能区首次测量了¹²C+⁹³Nb反应产生的8个核素及同质异能态的激发函数.使用包括非弹性激发和α转移道的简单耦合道模型,结合统计蒸发程序对实验结果进行拟合.计算结果能较好地重现强截面的中子蒸发道(xn)的激发函数.而对于弱的质子(xpyn)特别是α粒子(xαyn)蒸发道的截面,实验测量明显高于模型计算结果.α转移道与入射道耦合作为熔合反应的门庭态使垒下能区重离子熔合截面有很大的加强,实验测量与理论计算的比较表明对于¹²C+⁹³Nb反应系统在垒下能区可能存在着很强的α转移截面.     

用基态特征γ射线计算同质异能态反应截面的公式及其应用

根据人工放射性的生长与衰变规律, 推导出一个在特殊情况下用基态特征γ射线计算同质异能态反应截面的公式, 并据此公式用活化法以⁹³Nb(n,2n)^92mNb反应截面为中子注量标准对¹²⁸Te(n,2n)^127mTe反应截面进行了测量. 由能量为(14.1±0.2)和(14.6±0.3)MeV的中子引发的¹²⁸Te(n,2n)^127mTe反应截面值分别为(737±69)和(853±82)mb. 单能中子用T(d,n)⁴He反应获得, 其能量用铌锆截面比法测定. 为减小热中子的(n, γ)反应的影响, 在辐照过程中对样品进行了包镉处理.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.