核反应截面替代测量方法介绍

核反应截面替代测量方法是一种间接测定核反应截面的方法, 这种方法对于测定不稳定核的反应截面具有重要的意义。 详细介绍了替代方法的理论基础、 影响其精确性的重要因素, 以及基于该方法的3种变型方法: 外替代比率方法（ESRM）、 内替代比率方法（ISRM）和混合替代比率方法（HSRM）。 阐明了每一种方法的基本原理, 给出了相关的实验验证, 并且对每一种方法的优缺点进行了分析。发现在每一种方法中, 所求反应与替代反应之间的自旋 宇称不匹配始终是不可消除的一个影响因素。 但是经过实验验证, 替代方法（包括3种变型方法）也可以达到较高的精确度, 因而在不能够直接测定核反应截面的情况下, 该方法不失为一种很好的间接测量方法。The surrogate nuclear reaction approach plays an important role in the determination of nuclear reaction cross sections that are difficult to be measured directly. In this paper, we investigate its basis, factors affecting its accuracy, and its three variants: the external surrogate ratio method (ESRM), the internal surrogate ratio method (ISRM) and the hybrid surrogate ratio method (HSRM). Each method was described, and their applications or experimental tests were given, from which we could see their respective advantages and disadvantages. And it is found that the spin parity mismatch, or the (weak) Weisskopf Ewing limit equivalently, is an inherent limitation of the approach. It is also seen that the surrogate approach can reach a high accuracy, so it is a good indirect approach when the nuclear reaction cross sections are unavailable to be measured directly.     

Minimum audible movement angle as a function of signal frequency and the velocity of the source

Thresholds for the detection of the direction of travel of a moving sound source were determined in a single-interval, forced-choice paradigm. Both the rate at which the sound source is displaced (8 degrees-128 degrees/s) and the frequency of the signal to be localized (500-3700 Hz) affect dynamic spatial resolution. There is an inverse relationship between spatial resolution and the rate of travel, a finding that replicates an earlier observation on performance with sources displaced at high velocities [Perrott and Musicant, J. Acoust. Soc. Am. 62, 1463-1466 (1977)]. However, the magnitude of this effect depends on the actual velocities employed. Relatively small changes in spatial resolution are apparent for velocities below approximately 32 degrees/s. The significant frequency effect can be summarized as follows: Dynamic spatial resolution is better for signals below 1000 Hz than for signals above this value (within the range tested). Particularly poor resolution is evident for signals between 1300-2000 Hz. The present results indicate that signal frequency affects dynamic spatial resolution in a fashion similar to that which has been observed in the more common "static" localization test situation. There is no indication of an interaction between these two variables. These results provide additional support for the hypothesis that both static and dynamic spatial discrimination functions are dependent upon the same underlying mechanisms. The effects of velocity upon the spatial resolution problem, a unique aspect of the dynamic paradigm, can probably be explained without the necessity of additional hypothetical mechanisms in the auditory system (e.g., a specialized motion detector).     

Determination of time dependence of domain growth by direct observation of small metal clusters

The in situ growth of small gold clusters on amorphous carbon substrates has been measured by direct observation, utilizing high (single-atom) resolution scanning transmission electron microscopy. The time dependence of the width of the distribution of characteristic microscopic spatial frequencies in the samples was seen to obey a power-law behavior, HWHM = (t − t₀)^−a. The exponent measured, a = 0.15 ± 0.06, was in good agreement with scaling theories for domain growth. An excess of single atoms and small clusters was observed at all times, over that predicted by a uniform growth model of clusters. It is suggested that these support single-atom and few-atom cluster migration and activated accretion as important components of cluster growth at all times.     

Improved extended depth of focus full field spectral domain Optical Coherence Tomography

In Optical Coherence Tomography (OCT), both high axial and lateral resolutions are desired. While axial (z-axis) resolution is achieved by a broadband source, lateral (x-y axes) resolution is achieved by high NA lenses. However, high NA objectives result in decreased depth of focus (DOF). The small DOF makes it difficult to obtain single shot imaging of biological samples having large lateral dimension. In this work we incorporate special interfering phase mask allowing to extend the DOF of an OCT system and to allow imaging of samples without axial scanning.     

Phonons, rotons, and layer modes of liquid 4He in aerogel

We report the first observation of two-dimensional layer modes in both fully filled and partially filled aerogel. Using complementary high-energy resolution and high statistical precision neutron scattering instruments, and two different 87% porous aerogel samples, we show that the three-dimensional (3D) phonon-roton excitation energies and lifetimes of liquid 4He in aerogel are the same as in bulk 4He within current precision. The layer modes are the excitations that distinguish aerogel from the bulk rather than a difference in the 3D roton energy.     

Temperature,roughness and depth resolution in ion sputter profiles

The depth resolutions of evaporated silver layers on polished polycrystalline copper substrates are studied at various temperatures during argon ion sputtemg with AES. A detailed analysis of the profile shape at the interface reveals the nature of contributions to the terms governing interface resolution. The profiles are all accurately described by an error function leading edge followed by an exponential trailing edge. The characteristic of the trailing edge is governed by the development of roughness which depends on the depth, z, sputtered as z^0.875. The roughness is reduced at elevated temperatures by the action of surface diffusion such that the maximum reduction occurs at the highest temperature and the lowest sputtering rate. The characteristic of the leading edge is composed of three terms added in quadrature, (i) defect-enhanced diffusion of copper into the silver film, (ii) roughness as above, and (iii) a constant term due to film nucleation. In the present samples the increased interdiffusion at elevated temperatures and low sputtering rates largely offsets the improvements in topography so that, overall, the depth resolution appears to be a very weak function of temperature. However, in other systems where interdiffusion is small, the resolution could be greatly enhanced.     

PMP/Cu泡沫材料中Cu颗粒的三维分布

为观测和分析铜掺杂聚-4-甲基-1-戊烯(PMP/Cu)低密度泡沫材料中铜颗粒的三维空间分布,采用高分辨X射线断层扫描技术,扫描PMP/Cu泡沫材料样品,对铜颗粒在聚合物泡沫中的分布进行了成像分析。经过图像处理和三维重构,获得铜颗粒在PMP聚合物泡沫中的三维立体分布图。结果分析显示:铜纳米粒子在PMP泡沫中存在团聚现象;不同尺寸的团聚物形态呈现出明显的多样化特征,小颗粒团聚物趋于球形,大颗粒团聚物趋于不规则的短木棒状,与在电子显微镜下直接观测到的结果一致。研究表明,该技术可以在不破坏样品的前提下,实现对有机聚合物泡沫材料中掺杂金属颗粒空间分布情况的直接观测。     

Feasibility of Q-Band EPR Dosimetry in Biopsy Samples of Dental Enamel, Dentine and Bone

Electron paramagnetic resonance (EPR) dosimetry of tooth enamel in X-band has been established as a suitable method for individual reconstruction of doses 0.1 Gy and higher. The objective was to demonstrate the feasibility of using Q-band EPR in small biopsy tooth enamel samples to provide accurate measurements of radiation doses. Q-band spectra of small (<10 mg) irradiated samples of dentine and bone were studied to investigate the possibility of using Q-band EPR for dose measurements in those materials if there are limited amounts of enamel available, and there is no time for the chemical sample preparation required for accurate X-band measurements in dental enamel. Our results have shown that Q-band provides accurate measurements of radiation doses higher than 0.5 Gy in tooth enamel biopsy samples as small as 2 mg. Q-band EPR spectra in powdered dentine and bone demonstrated significantly higher resolution and sensitivity than in conventional X-band measurements.     

Detection threshold in muscovite mica: Influence of the observation tool

For the observation of nuclear tracks, Atomic Force Microscopy (AFM) is a useful technique. In our study, we have irradiated a muscovite mica sample using 600 keV oxygen ions. This ion's energy is well below the detection threshold predicted by the existing models. The samples were visualized at high resolution with an AFM device. Before chemical etching no tracks were visualized on the surface at an atomic level. However, defects must have been initiated because tracks became observable after a brief etching time. Our results confirm that the detection threshold is influenced by the observation tool. In this article we provide information concerning the “observability” and “etchability” of latent tracks.     

Atomic structures of silicon and metal surfaces; pulsed-laser tof atom-probe and field ion microscopy

The atomic structure of a solid surface can be imaged with the field ion microscope and the chemical species of surface atoms can be identified by the time-of-flight atom-probe. By combining a pulsed-laser technique to field ion microscopy, atomic processes in surface reconstruction and growth of thin films can be studied with a resolution of 2.5 Å, and in time steps of a few nanoseconds. The mass resolution and material applicability of a pulsed-laser time-of-flight atom-probe are greatly improved. Thus materials of poor conductivity such as high purity silicon can be analyzed with excellent mass resolution. It is also ionion energy analyzer with an accuracy and resolution of 2 parts per 100 000 and an ion reaction and dissociation time analyzer of 20 fs time resolution. Some recent studies with these techniques such as (1) surface reconstruction of Pt and Ir(001) and (110) surfaces, (2) observation of well ordered and atomically resolved images of pure silicon surfaces and surface reconstruction of many surfaces of silicon, and (3) formation of multiple charge cluster ions and dissociation of compound ions by atomic tunneling in an electric field etc., will be briefly described. We want to emphasize that recent studies of Si and metal surfaces are concerned with atomic structures of thermally equilibrated surfaces, and not with field evaporated surfaces as in earlier studies.     

Observation of subcellular nanostructure of single neurons with an illumination mode photon scanning tunneling microscope

We report about the observation of microtubules lying underneath the cell membrane of neural process in neurons with a resolution as high as that of an electron microscope by an illumination mode photon scanning tunneling microscope. Nanoapertures used in our observations were fabricated by means of selective chemical etching and metal coating of an optical fiber. The narrowest observed tube has got an average diameter of 26 nm. Comparing this with its nominal value of 25 nm, the difference which is considered as a measure of resolution (δ) is 1 nm implying a resolution comparable to that of an electron microscope in imaging dielectric specimens. This was possible due to the presence of a boundary between the glass and the metal coating and also due to the use of an aperture of almost the same size as that of the microtubule that enhances the detection.     

实现同步轨道（GEO）高分辨力对地观测的技术途径（上）

在地球静止同步轨道（GEO）上实现高分辨力对地观测，具有一系列独特优点，远为其它轨道所不及。然而，对于36000km的远程高分辨力可见波段观测，要求望远镜必须具备20m以上口径的主镜。传统的空间相机，如果要有如此大的口径，其总质量将超过1000t，无法发射到GEO上。无支撑薄膜望远镜和大口径衍射望远镜，可以大幅度降低主镜质量面密度，从而降低整个相机系统的总质量，可算是一种极好的技术途径。分步发射与在轨装配，则提供了可供此类观测系统实施从地面转运到GEO的技术手段。基于变换成像原理的傅里叶望远镜，将高分辨力的取得，由增大接收口径转变为加大发射间隔，用大面积回波能量探测加上傅里叶分量重构，取代常见的目标图像直接探测，突破了远程高分辨力观测的致命瓶颈。近完美透镜为突破衍射极限提供了可能性，从而为超分辨力观测开拓出一片科学的新天地。负折射率材料（左手型材料）可制成完美透镜，而光子晶体是负折射率材料的热门选择之一，基于表面等离子激元（SPP）的光子器件则是其另一种选择。     

Quantitative XPS imaging—new possibilities with the delay-line detector

X-ray photoelectron spectroscopy (XPS, ESCA) is an ideal tool for identifying differences in surface chemistry. In the past, it has lacked the spatial resolution as well as the performance of elemental or even chemical state imaging, to be of significant use in detecting most microscopic surface phenomena. The recent development of improved micro- or small spot-XPS systems with near-micron spatial resolution as well as outstanding chemical state image performance has opened up a significant opportunity to undertake more detailed studies of micro-structured or micro-patterned surfaces or technical samples with locally distributed impurities. The introduction of a new detector type, the delay-line detector (DLD), to XPS-equipments allows for the first time the acquisition of quantifiable XPS images. This study is intended primarily to explore the capabilities of quantitative ESCA-imaging with respect to the possibilities and limits.     

Theoretical analysis of the surface thermal wave technique for measuring the thermal diffusivity of thin slabs

We present a theoretical analysis of a photothermal radiometry method of measuring thermal diffusivity, in which thermal radiation is detected from a small area, displaced by known distances from an area of modulated optical excitation. Expressions for evaluating the measurements and their main systematic errors have been worked out for thermally thin slab samples. The measurements, data and error analysis techniques are illustrated with experiments on metallic and polymeric samples. These show that the main systematic errors are associated with the spatial resolution of the apparatus and heat losses to air and thermal radiation.     

基于精密太阳光谱辐射计的气象辐射观测

目前,气象业务观测普遍采用的积分型太阳辐射观测仪器存在观测数据信息量少、数据差异大的观测瓶颈,已无法满足目前众多应用科学研究领域对太阳光谱辐射精细化观测的需求,具有高光谱分辨率的精密光谱辐射计的仪器研制及观测方法与技术已成为太阳辐射观测的前沿科技问题。在此背景下,为解决气象领域太阳辐射的精细化观测问题,开展了深入的科学研究与技术开发工作。重点阐述了仪器开发成果和数据观测分析方法,首先介绍了开发研制的用于地基太阳光谱辐照度观测的光谱辐射计系统。光谱辐射计的分光系统采用了平场凹面光栅结构,具有低杂散光、高收光效率和高可靠性的特点,尤其适用于长期无人值守的户外观测。系统所采用的平场凹面光栅的像差校正特性对于300～1 100 nm这种宽谱段的应用来讲更为合适,在整个谱段范围内光谱分辨率变化很小,不同波长通道的带宽基本一致,使用25 μm狭缝时光谱分辨率(FWHM)约为2 nm,像素采样间隔小于0.5 nm。对于太阳辐射观测来讲,这是一种谱段范围和分辨率都与需求十分匹配的专用光谱辐照度观测仪器。其次,在观测数据的基础上,阐述和分析了气象等领域的光谱应用观测方法。太阳辐射照度分布的能量通过不同参数化模型约束的接收系统收集,将太阳光谱辐射在半球天穹中的变化及分布进行约束并划分为水平总辐照度(GHI),法向直接辐照度(DNI)和水平散射辐照度(DHI)三种光谱辐照度辐射分量,阐述了基于GHI,DNI和DHI三种观测形式下的数据特征与用途。其中,GHI是地表实际辐照度水平,适用于太阳能资源评估;DHI反映大气和云态;DNI作为直接透射形式,可用于计算日照时数和分析大气参量。并且,进一步分析了观测形式、光谱特征与地理(经度、纬度、海拔高度、大气质量)及气象参数(云量、大气吸收)之间的互易演算关系。与传统的波长积分式辐射观测相比,太阳光谱辐射计为辐射能量观测增加了波长信息维度。从DNI形式的光谱辐照度数据中可以看出,不同波长之间的辐射能量变化显著,而这些变化与大气变化密切相关。因此,太阳光谱辐照度数据不仅仅是为业务观测提供更精细化的太阳辐射信息,更提供了丰富的辐射能量的变化信息通道,利用特征波长维度的辐射信息,可进一步通过模型反演计算气溶胶光学厚度、臭氧、水汽等大气参数。通过精密太阳光谱辐射计,可将纳米分辨率水平的太阳光谱辐照度作为基础业务运行数据,提供精细化的太阳辐射分布及变化信息用于气象与气候模型、光伏资源评估与生态环境等研究;同时也为辐射波长分布中所蕴含的气候、农业、生态等领域关心的各种通量监测和演化关系研究提供了有力的数据信息及观测工具。     

Studies of imaging experiment for photon scanning tunneling microscopy

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High resolution study of the group V impurities absorption in silicon

High resolution spectra of P-, As- and Sb-doped Si have allowed the determination of the “natural” width of the impurity lines for concentration in the range of 10¹⁴ at cm^?3 and below. The width of the P-lines makes possible the observation of the 5p₀ line, very close to the 4p_± line. In the Sb- and As-doped samples, an effect similar to concentration broadening is observed. Results on P- and Bi-doped samples at lower resolution give evidence of the observation of the 3d₀(P) line and of internal Stark effect in the Bi-doped sample.     

高分辨率及高灵敏度小动物PET研究进展

作为一种高灵敏度且具有定量测量能力的功能分子影像技术,小动物PET越来越广泛地用于各种生物医学研究,例如疾病动物模型研究、新药物研发和新治疗方法评估等。首先回顾小动物PET成像系统的发展历史、效率和空间分辨率等性能的改进和产业化;其次,讨论了影响PET空间分辨率和效率的各种因素,包括晶体大小、探测器几何、正电子射程、光子非共线效应、图像重建算法和阻碍PET系统同时达到高空间分辨率和高效率的相互作用深度不确定效应;最后,介绍了小动物PET成像系统在以下几个方面的取得的最新进展:（1）高密度、小的光衰减常数和高光产额的闪烁晶体;（2）体积小、增益大、时间性能好、工作电压低和磁兼容的新型硅光电倍增管光探测器;（3）各种深度测量PET探测器,详细介绍了一个可达到分辨0.43 mm×0.43 mm×20 mm晶格和达到2.4 mm深度分辨率的双端读出探测器;（4）使用深度测量探测器的小动物PET成像系统,详细介绍了一个使用高分辨率双端读出探测器,全视野达到0.55 mm平均位置分辨率的小动物PET原型系统;（5）磁兼容插件式小动物PET成像系统和PET/MRI同时成像的优点;（6）小动物PET图像重建和数据校正的特点、传统的滤波反投影算法和新的迭代算法的优缺点和PET图像重建算法未来的发展方向。As the most sensitive and quantitative molecular imaging technique,small animal positron emission tomography (PET) has become a widely used tool in biomedical research such as in animal model of human disease,development of new drugs and the evaluation of new therapeutics.In this paper,first the history,the efforts to improve the spatial resolution and sensitivity as well as the commercialization process of small animal PET scanner are reviewed.Then the factors that affect the spatial resolution and sensitivity of PET scanner such as crystal size,detector geometry,positron range,photon noncollinearity and imaging reconstruction are discussed in detail.The depth of interaction effect which hinders the simultaneous achievement of PET spatial resolution and sensitivity are also discussed.Finally the recent progress made in the following areas of small animal PET instrumentation are introduced:(1) high density,short light decay constant and bright scintillator,(2) compact,high gain,good timing resolution,low bias voltage and MRI compatible silicon photomultiplier,(3) depth encoding detectors by using different methods,a detector using dual-ended readout,identifying 0.43 mm×0.43 mm×20 mm crystals and achieving a 2.4 mm depth of interaction resolution was introduced in detail,(4) small animal PET scanners using depth encoding detectors,a prototype scanner using high resolution dualended readout detectors and achieving an average of 0.55 mm spatial resolution in the whole field of view was introduced in detail.(5) MRI compatible small animal PET inserts and the advantage of simultaneous PET/MRI imaging,(6) image reconstruction and data correction of small animal PET,the filter back projection and iterative reconstruction algorithms are compared and a few key directions of PET image reconstruction will be presented.     

实现同步轨道(GEO)高分辨力对地观测的技术途径(下)

在地球静止同步轨道(GEO)上实现高分辨力对地观测,具有一系列独特优点,远为其它轨道所不及。然而,对于36 000 km的远程高分辨力可见波段观测,要求望远镜必须具备20 m以上口径的主镜。传统的空间相机,如果要有如此大的口径,其总质量将超过1 000 t,无法发射到GEO上。无支撑薄膜望远镜和大口径衍射望远镜,可以大幅度降低主镜质量面密度,从而降低整个相机系统的总质量,可算是一种极好的技术途径。分步发射与在轨装配,则提供了可供此类观测系统实施从地面转运到GEO的技术手段。基于变换成像原理的傅里叶望远镜,将高分辨力的取得,由增大接收口径转变为加大发射间隔,用大面积回波能量探测加上傅里叶分量重构,取代常见的目标图像直接探测,突破了远程高分辨力观测的致命瓶颈。近完美透镜为突破衍射极限提供了可能性,从而为超分辨力观测开拓出一片科学的新天地。负折射率材料(左手型材料)可制成完美透镜,而光子晶体是负折射率材料的热门选择之一,基于表面等离子激元(SPP)的光子器件则是其另一种选择。     

A history of scanning electron microscopy developments: towards "wet-STEM" imaging

A recently developed imaging mode called "wet-STEM" and new developments in environmental scanning electron microscopy (ESEM) allows the observation of nano-objects suspended in a liquid phase, with a few manometers resolution and a good signal to noise ratio. The idea behind this technique is simply to perform STEM-in-SEM, that is SEM in transmission mode, in an environmental SEM. The purpose of the present contribution is to highlight the main advances that contributed to development of the wet-STEM technique. Although simple in principle, the wet-STEM imaging mode would have been limited before high brightness electron sources became available, and needed some progresses and improvements in ESEM. This new technique extends the scope of SEM as a high-resolution microscope, relatively cheap and widely available imaging tool, for a wider variety of samples.