钛酸钡中极化团簇的特征弛豫时间随温度的变化规律

BaTiO3中存在极化团簇已经被大量实验所证明,并且极化团簇的空间、时间信息以及随温度的演化信息对介电性质有着重要影响。因此探测BaTiO3中极化团簇的相关信息对于理解其功能和揭示相变机理具有重要意义。本实验利用光子相关谱方法,在精确温控的条件下,观测到BaTiO3中300nm周期长程极化团簇微秒量级的特征弛豫时间τc,并揭示了该时间在TC附近4K温度范围内变化的细节特征。实验表明光子关联谱是研究铁电动力学的有效方法。     

3 超短脉冲激光与原子团簇相互作用实验研究

实验研究了超短脉冲激光与原子团簇相互作用过程中各种实验条件对团簇吸收激光能量的影响。实验发现高Z稀有气体（Xe）以及较高的气体压力都更易形成大团簇，对激光能量的吸收较高。还研究了激光波长（744与248nm）、激光强度以及偏振态等对吸收效率的影响。结果表明，短波长激光更易被团簇吸收；在一定强度范围内（10^15～10^16W／cm^2），随激光强度的增强，团簇对激光的吸收效率也增高；P极化光比S极化光更易被团簇吸收。     

超短脉冲激光与原子团簇相互作用实验研究

实验研究了超短脉冲激光与原子团簇相互作用过程中各种实验条件对团簇吸收激光能量的影响。实验发现高Z稀有气体(Xe)以及较高的气体压力都更易形成大团簇,对激光能量的吸收较高。还研究了激光波长(744与248nm)、激光强度以及偏振态等对吸收效率的影响。结果表明,短波长激光更易被团簇吸收;在一定强度范围内(1015~1016W/cm2),随激光强度的增强,团簇对激光的吸收效率也增高;P极化光比S极化光更易被团簇吸收。利用能量计测量了不同实验条件下激光的吸收效率,室温下,2MPa Xe气体形成团簇对激光的吸收效率达50%,并利用飞行时间谱仪测量了离子…     

荷能团簇碰撞沉积装置中飞行时间质谱仪的物理设计

介绍了荷能团簇飞行时间质谱仪的原理及其在荷能团簇碰撞沉积装置中的物理设计。对实验中出现的若干问题进行了探讨,并提出了解决的措施。     

基于AKMC方法研究Mn对Cu团簇析出的影响

Cu团簇析出是影响FeCu合金体系安全服役的主要因素之一。本文基于原子动力学蒙特卡罗（AKMC）方法研究了热老化条件下,合金元素Mn对Fe-1.34at.%Cu-Xat.%Mn（X为0、0.27、1.2、3、5）合金中Cu团簇析出的影响。研究结果表明,随着体系中Mn含量的增加,析出形核的纳米级Cu团簇的数密度不断增加;Mn含量对形核Cu团簇的平均尺寸影响不大。团簇中主要成分为Cu;团簇中Mn含量随初始基体中Mn含量的增加而增加。合金元素的成团参与百分比决定了团簇平均尺寸。Cu-Vac复合体较强的扩散能力及其较远的扩散距离是造成Cu团簇析出的主要因素;而Mn的加入会抑制Cu-Vac复合体的可移动距离和可移动能力,从而提高Cu团簇的数密度。合金元素Mn的加入会影响形核Cu团簇的尺寸、数密度,从而影响Cu团簇引起的硬化效应。     

氘团簇离子(d3+)固体与相互作用过程中的团簇行为研究

讨论了由三个氘原子组成的氘团簇离子(d3+)束与独立氘离子束在轰击固体靶时,在原子过程和D-D核聚变过程中体现出的差别.对氘团簇与固体靶相互作用的机理进行了分析.     

碳团簇C+n(n=1—5)注入NaCl晶体的研究

能量为 0 .6MeV/C荷能碳团簇离子Cn+(n =2— 5)注人到NaCl单晶 ,利用TRIM程序对碳团簇在NaCl单晶中的射程进行模拟 ,碳团簇NaCl单晶内存在一定长度的“团簇区域”。光学吸收谱表明 :由于团簇区域的存在 ,不同碳离子团簇辐照产生的缺陷种类浓度都有很大不同 ,较大团簇会产生V2 和V3色心 ,色心浓度也较大。     

重金属团簇运移实验研究

设计一套可以观测重金属运移的装置,实验发现：当重金属中加入U、Th等α放射源后,放射源的α衰变能够使重金属产生明显的向上运移,这是因为重金属与He核形成团簇,当团簇的密度比空气小时,重金属团簇便可以向上运移。     

碳团簇Cn+(n=1-5)注入CR39树脂的吸收光谱研究

利用2×1.7串列加速器产生的团簇离子Cn+(n=l-5)注入到CR39树脂中,树脂的光吸收性质因注入的团簇离子的剂量、剂量率以及团簇中所含原子的个数不同而有不同的变化.该项研究表明团簇与固体相互作用时团簇效应是通过电子阻止来体现的.     

团簇尺度的瑞利散射测量中光电倍增管信号刻度与归一化处理

利用光电倍增管测量团簇的瑞利散射,信号幅度与团簇源背压有关,也与光源强度和光电倍增管工作电压有关.当团簇源背压变化范围较大时,散射信号幅度变化可能导致光电倍增管信号超出线性范围.为此,在不同的光源强度、不同的工作电压下对光电倍增管输出信号进行了刻度,得到了输出信号幅度随光源强度、工作电压之间的关系.用此关系.对不同条件下的实验数据进行归一化处理,得到了团簇散射因子随团簇源背压的关系曲线,与同类实验和理论结果相符.     

Growth of 4" diameter polycrystalline diamond wafers with high thermal conductivity by 915 MHz microwave plasma chemical vapor deposition

Polycrystalline diamond (PCD) films 100 mm in diameter are grown by 915 MHz microwave plasma chemical vapor deposition (MPCVD) at different process parameters,and their thermal conductivity (TC) is evaluated by a laser flash technique (LFT) in the temperature range of 230-380 K.The phase purity and quality of the films are assessed by micro-Raman spectroscopy based on the diamond Raman peak width and the amorphous carbon (a-C) presence in the spectra.Decreasing and increasing dependencies for TC with temperature are found for high and low quality samples,respectively.TC,as high as 1950 ± 230 W m-1 K-1 at room temperature,is measured for the most perfect material.A linear correlation between the TC at room temperature and the fraction of the diamond component in the Raman spectrum for the films is established.     

Electrical and optical properties of MWNTs/HDPE composites in Terahertz region

Optical and electrical properties of composites,prepared by filling of high density polyethylene(HDPE) with two kinds of multi-walled carbon nanotubes(MWNTs) differing in diameters,were explored by terahertz time-domain spectroscopy(THz-TDS) in the frequency range from 0.2 to 1.6 THz.It is found that composite with larger-diameter MWNTs possesses larger absorption coefficient and conductivity at the same concentration.The real part of the ac conductivity of the composites follows a power law dependence on frequency.And the power index is around 0.75 regardless of the MWNT concentration and diameter.The experimental data were analyzed with Cole-Cole equation under the assumption that the conductive clusters dispersed in the polymer matrix behave like dipoles and contribute mainly to the dielectric loss.It is found that both of the composites have similar values of relaxation time and distribution parameter.With increase of the MWNTs concentration,the relaxation time increases and tends to saturate at 0.7 ps after passing through the percolation threshold.     

Characterization of crystallisation processes with electrical impedance spectroscopy

The surfaces of crystalline particles are often charged and therefore crystals have an electrical double layer associated with their surfaces when, for example, suspended in an aqueous medium. Under the influence of an external electric field, an electrical dipole moment can be induced due to polarization of the electrical double layer. The complex impedance, conductivity, relaxation time and phase shift caused by the polarization are all related to particle characteristics, e.g. the size, polymorph and concentration. The method of electrical impedance spectroscopy (EIS) provides, potentially, a capability for characterizing the particles in colloidal suspensions. Here some preliminary observations of physical-chemistry fundamentals relating to the use of electrical impedance spectroscopy, potentially, for particle sizing in crystallisation processes are reported. Firstly, the effects of l-glutamic acid (LGA) solids concentration, solute concentration and temperature on the measured EIS spectra were studied. The results show that the effects of solid LGA concentration and solute concentration on the relaxation frequency and phase angle are very small. Secondly, the temperature effect was analysed. By deducting the contribution due to the changes in concentration and temperature from the total change in relaxation frequency, the experimental observations, although preliminary in nature, suggest that the crystal size can be related directly to relaxation frequency (in this study, the shape of LGA crystals is assumed to be spherical so the crystal size means the diameter of the sphere). The experimental observations can be explained with either static polarization models or particle vibration models. On-line measurement of electrical impedance spectra associated with LGA nucleation-growth processes are presented. The information content of the complex electrical impedance, phase angle shift and relaxation times of the crystal suspensions during a crystallisation process is assessed. The results show that during nucleation the imaginary part of the electrical-impedance response changes significantly and the relaxation frequency decreases during the growth of crystals. The longer-term objective is to develop a new spectroscopic measurement method and further, a spectroscopic tomography technique for on-line measurement of the spatial distribution of particle size in particle suspensions in liquid media.     

Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

Two experimental techniques have been used to quantify the atomic oxygen density in the case of hot air plasma generated by a microwave (MW) resonant cavity. The latter operates at a frequency of 2.45 GHz inside a cell of gas conditioning at a pressure of 600 mbar, an injected air flow of 12 L/min and an input MW power of 1 kW. The first technique is based on the standard two photon absorption laser induced fluorescence (TALIF) using xenon for calibration but applied for the first time in the present post discharge hot air plasma column having a temperature of about 4500 K near the axis of the nozzle. The second diagnostic technique is an actinometry method based on optical emission spectroscopy (OES). In this case, we compared the spectra intensities of a specific atomic oxygen line (844 nm) and the closest wavelength xenon line (823 nm). The two lines need to be collected under absolutely the same spectroscopic parameters. The xenon emission is due to the addition of a small proportion of xenon (1% Xe) of this chemically inert gas inside the air while a further small quantity of H₂ (2%) is also added in the mixture in order to collect OH(A¬X) and NH(A-X) spectra without noise. The latter molecular spectra are required to estimate gas and excitation temperatures. Optical emission spectroscopy measurements, at for instance the position z=12 mm on the axis plasma column that leads to a gas measured temperature equal to 3500 K, an excitation temperature of about 9500 K and an atomic oxygen density 2.09×1017± 0.2×10¹⁷ cm ⁻³ . This is in very good agreement with the TALIF measurement, which is equal to 2.0×10¹⁷ cm ⁻³ .     

Parametrization of the total photon mass attenuation coefficients for photon energies between 100 eV and 1000 MeV

A convenient way of generating mass attenuation coefficients for data analysis in various fields of X-ray spectroscopy is by means of semi-empirical schemes. However, the validity of most of the existing schemes is limited to relatively narrow energy intervals (typically 1–50 keV) and their accuracy is usually poor especially in regions near absorption edges. A few years ago, we use a new semi-empirical scheme that enabled us to fit, for the first time, photon data for all elements in the very wide energy range, i.e. between 0.1 and 1000 keV. The scheme was found flexible enough to provide excellent fit to the most recent compiled photon cross section data in the entire energy range. It was based on fitting data to an exponential function with the addition of a Klein–Nishina term to account for dominant incoherent scattering at higher energies. In the present work, our former scheme is extended beyond the pair-production threshold (1.02 MeV) all the way to 1000 MeV. An interactive MS Windows based computer program for generating, printing and displaying mass attenuation coefficients based on the proposed scheme has been developed.     

Subject index

In 1965 eight surveillance subassemblies were placed in row 12 of the EBR-II sodium-cooled fast breeder reactor with an irradiation temperature near the sodium-inlet temperature of 371°C. At the same time, two other surveillance subassemblies were placed in the primary storage basket, which receives minimal neutron exposure but is immersed in primary sodium and experiences a temperature of 371°C. Each of the subassemblies contained 18 preloaded springs made of Inconel X750. Springs from four of the in-core subassemblies and one subassembly from the storage basket have been evaluated to determine irradiation-enhanced deformation rates to neutron exposures of 4.2 dpa.It was found that the creep coefficient derived from the stress relaxation measurements on Inconel X750 springs was 1.0 × 10^?12 (Pa-dpa)^?1 for springs irradiated up to 4.2 dpa (3751 d) at an in-reactor temperature of 371°C. The relaxation behavior was adequately described by a creep law that was linear in neutron fluence and applied stress. Springs encapsulated in helium showed identical in-reactor relaxation rates to springs exposed to the flowing primary sodium. The creep coefficient derived from the present work on Inconel X750 springs was shown to be the same as the creep coefficients determined from various austenitic stainless steel alloys.     

Vacancy-type defects near Al surface studied by slow positron annihilation spectroscopy before and after He implantation

The vacancy-type defects He_nV_m near Al surface before and after He⁺ implantation and their evolutions with annealing temperatures and aging time have been investigated by mono-energy slow positron annihilation spectroscopy (SPAS) with S parameters. The results show that many vacancies are produced during the sample preparation process, which can be re-occupied by Al atoms during annealing, Al⁺ and MeV He⁺ implantation. S parameters denote the concentration and size of He_nV_m clusters induced by He⁺ implantation in Al. The higher fluence of He implanted, the larger S parameters will be, indicating more He_nV_m clusters produced. S parameters decrease with the increase of annealing temperatures until the fastest change temperature, and then an opposite or minor change occurs depending on the fluence of He implanted in Al, showing that the concentration and size of He_nV_m clusters will vary with the annealing temperatures. Aged at RT for some time, the concentration and mean size of He_nV_m clusters in Al will get smaller and larger, respectively, resulting in the decrease of S parameters with the aging time. In conclusions, the evolution of vacancy-type defects He_nV_m near Al surface after He⁺ implantation depends on the annealing temperatures, He concentration and aging time.     

Improvement of a temperature response function for divertor heat flux monitoring in fusion devices

Temperature response functions have been developed to investigate sensor design and divertor heat flux estimation in magnetically confined plasmas. The time-dependent heat flux can be derived by fitting the response function to experimental thermocouple(TC) data. Because the TC signals have a time delay to transit events such as discharge start or confinement transition, the time delay is taken into account in a temperature response function. Such a function accurately describes the signal from ...     

用光子源敷贴治疗时血管瘤中剂量分布的蒙特卡罗计算

用蒙特卡罗法计算了用10-366keV的光子源敷贴治疗时一种简化血管瘤模型中的剂量分布。计算结果表明,临床治疗时,光子能量应选在30keV附近,这样既有很好的治疗效果,又可适当减少对正常组织的照射。用~(125)I对30余例混合型、海绵状血管瘤进行的治疗疗效显著,随访中没有发现皮肤溃烂等现象。同时给出了10Gy的瘤体平均剂量对应的各种能量下的光子数。