X射线荧光分析中X射线管原级能谱分布的测定

确切知道X射线管激发的原级能谱分布是X射线荧光分析中的一个重要前提,所用能谱分布函数的准确度大大影响了最终的测量结果。提出利用间接测量法,选用合适的参量模型来描述X射线的原级能谱分布。依靠实验测得的厚靶纯元素样品的荧光强度,利用已知的理论公式,建立非线性方程,优化得到参量模型中的参量值。通过比较实验测得的元素的荧光强度值和利用得到的能谱分布函数计算的理论值,证明此种方法是可行的。     

钚体源样品γ能谱计算的蒙特卡罗方法

提出了钚体源样品γ能谱分步计算的蒙特卡罗模型和方法.采用分步和直接计算两种方法对球壳形钚体源样品的γ能谱进行了模拟计算.用实验测量的γ能谱验证了计算结果的可靠性，计算结果与实验测量值在10%的误差范围符合.通过对Steve Fetter模型的模拟计算表明：对于外面包有若干屏蔽层的钚体源样品大系统，采用分步方法进行能谱计算，可以使结果快速收敛.     

钚体源样品r能谱计算的蒙特卡罗方法

提出了钚体源样品r能谱分步计算的蒙特卡罗模型和方法．采用分步和直接计算两种方法对球壳形钚体源样品的r能谱进行了模拟计算．用实验测量的r能谱验证了计算结果的可靠性，计算结果与实验测量值在10％的误差范围符合,通过对Steve Fetter模型的模拟计算表明：对于外面包有若干屏蔽层的钚体源样品大系统，采用分步方法进行能谱计算，可以使结果快速收敛．     

α能谱峰形函数及其拟合参数初始值获取

(1. 西南科技大学 核废物与环境安全国防重点学科实验室, 四川 绵阳 621010;2. 四川理工学院 化学与环境工程学院, 四川 自贡 643000;3. 成都理工大学 地质灾害防治与地质环境保护国家重点实验室, 成都 610059;4. 中国工程物理研究院 核物理与化学研究所, 四川 绵阳 621900) 根据能谱的形成机理,建立了一种能谱峰形函数,提出基于矩估计法确定该峰形函数的拟合参数初始值的方法。以数理统计为基础,分别通过峰形函数和离散谱峰数据计算均值、方差和三阶中心矩建立方程组求解获取拟合参数的初始值。通过连续气溶胶检测仪探测的氡子体能谱和低本底能谱仪探测的238Pu面源能谱对该峰形函数模型和初始值获取方法进行了测试。结果表明:从低重合度到高重合度,该峰形函数模型都能得到较好的应用;基于矩估计法确定该峰形函数的参数初始值能够使该峰形函数较好地拟合能谱数据。该方法在采用计算机自动能谱拟合分析中具有较强的实用性。     

基于蒙特卡罗方法的α放射源能谱测量模拟北大核心CSCD

运用蒙特卡罗方法建立PIPS-α谱仪的腔室模型,模拟谱仪对α面源(238Pu)的能谱测量,通过改变放射源与探头之间的距离,模拟不同条件下α粒子的射线能谱,同时,对不同探源距条件对α射线能谱的影响进行分析;另一方面,使用谱仪在不同探源距的情况下进行α能谱实验测量,获得不同条件下α射线能谱;最后,将模拟与实验的结果进行对比,分析实验测量结果与模拟结果的相对误差,并对模拟过程及模型参数进行校正,对校正后的模型进行实验验证,使其能够应用到其他α放射源的能谱测量中,并且使其可用于单能α粒子的能谱研究,研究结果也可为α能谱测量技术提供依据,为α能谱解谱技术提供数据支持。     

294MeV 20Ne+159Tb反应中出射α粒子的研究

在294MeV Ne束轰击Tb靶的反应中,用ΔE-E望远镜测量了10°—150°发射的α粒子能谱,并用运动源模型拟合了所得的实验能谱,得到与前角度源、中等速度源、熔合蒸发源的有关参数.计算谱很好地复现了实验能谱的形状、峰位信数值,角分布也得到极好的模拟.实验所得的发射α粒子截面为3300mb,运动源模型计算值为3700mb.     

对10~(14)eV以上初级宇宙线成份的推论

拟合10~(14)eV以下初级宇宙线核成份能谱的实验数据,并将它们一直外推到发生拐折的能量。按“刚度切割模型”,适当选择拐折能量,使分成份能谱之和与总粒子谱相符,来推论10~(14)eV以上初级宇宙线成份。所得能谱与相互作用模型无关。     

微观核芯+两准粒子模型中热核148—158Sm的比热容及其相变

应用微观核芯+两准粒子模型制备偶148—158Sm同位素的零温度能谱, 其基态带、β带、γ带和部分高自旋态能谱值与最新实验结果符合得较好; 采用正则系综理论, 计算出核的有限温度比热容.基于比热容峰是相变信号，给出了统一描述核发生热激发模式相变、从核超流相到正常相相变和核形状相变的可能性.讨论了两准粒子顺排态能量和指认, 以及核形状的热稳定性.     

基于基效应分解的多谱投影序列盲分离算法研究

在常规CT成像系统中,发出的X射线是连续能谱的,导致重建图像出现硬化伪影,影响了材料组分区分,无法进行定量表征。解决这一问题的关键在于实现多能谱CT成像,利用多个窄能谱段或单能量CT图像,提高组分与图像灰度的对应性。相对于传统CT,能谱CT具有更强的组分区分能力,有利于实现物体组分的定量分析。现有的基于光子计数探测器多谱CT在成像时间分辨率和空间分辨率存在局限,基于能谱滤波的多谱CT能谱区分度受限。而基于变电压多谱投影序列盲分离的多谱CT,通过分解连续能谱投影,获取窄能谱投影,进而实现能谱CT成像,确保物质组分与重建图像灰度值的对应性,实用性较强。但是由于X射线能谱和物体组分的未知,在盲分离过程中,衰减系数未知,并且能谱划分是不确定的,导致窄能谱CT重建图像的能量指向性不强,对应能量值与参考能量偏差偏大,影响组分定量分析。因此,针对盲分离中能谱划分不确定性和重建图像能量指向性问题的开展研究。利用衰减系数的光电效应和康普顿效应分解,构建能量约束,消除能量的不确定性,降低分解所得投影重建图像的能量与参考能量值的偏差。在基于以残差的局部方差和最小为优化目标的分解模型中,将分解模型中的衰减系数按光电效应和康普顿效应分解为能量项和材料项,利用能量项的可预知性,依据预先划分的窄能谱段设置其值,固定各分解投影对应的窄能谱段,作为对能量的约束条件。求解所得各分解投影为能量已知投影,对其重建可得到能量确定的各窄能谱段的图像。选择衰减系数相近的硅铝材质构成外硅内铝圆柱体进行实验验证,在有能量约束的求解结果中,硅铝衰减系数与参考值偏差小于无能量约束,所得重建图像中硅铝变化率与理论值趋势较一致,能量指向性强,与参考能量偏差降低。结果表明,所提方法解决了基于变电压序列盲分离多谱CT成像的能量指向问题,能谱分辨率更高,组分表征更准确。     

关于引入拆对几率概念探索原子核高自旋态

根据原子核转动系统中科氏力反对对力和转动重排,本文提出了拆对几率的物理概念探索原子核高自旋态.我们认为,拆对过程是从渐变到突变又到渐变的过程.按照拆对几率 P_I 的概念和粒子加转子模型,可以得到原子核的转动能谱公式?用这个公式计算了五十多个原子核的能谱,计算结果与实验值满意符合,并能再现出实验上观察到的?_eff～ω_eff²图的各种反弯现象.     

Reversal of Magnetisation in Ising Ferromagnet by the Field Having Gradient

We have studied the reversal of magnetisation in Ising ferromagnet by the field having gradient along a particular direction. We employed the Monte Carlo simulation with Metropolis single spin flip algorithm. The average lifetime of the metastable state was observed to increase with the magnitude of the gradient of applied field. In the high gradient regime, the system was observed to show two distinct region of up and down spins. The interface or the domain wall was observed to move as one increases the gradient. The displacement of the mean position of the interface was observed to increase with the gradient as hyperbolic tangent function. The roughness of the interface was observed to decay exponentially as the gradient increases. The number of spin flip per site was observed to show a discontinuity in the vicinity of the domain wall. The amount of the discontinuity was found to diverge with the system size as a power law fashion with an exponent 5/3.     

Fim observation of an iron deposited tungsten tip

An iron-deposited tungsten tip was observed with a field ion microscope. The observed features were classified into five types corresponding to the various substrate temperatures. Epitaxial growth was observed at substrate temperatures ranging from 100°C to 500°C, though the parallelism was not perfect. An epitaxially grown film was observed only on one side of a tip cap at a low temperature. The film spread to the entire tip cap at a higher temperature. Diffusivity of the deposited iron was estimated from the observed migration of the iron atoms. Images which implied the formation of an alloy of kon and tungsten were obtained at 550–660°C. When the substrate temperature exceeded 700°C, iron atoms were not observed on the tip cap. These sequential change corresponding to the substrate temperatures will be discussed in relation to the surface diffusion of the deposited iron and substrate tungsten atoms.     

Ultra high energy cosmic rays

The current status of Ultra High Energy Cosmic Rays (UHECR) is reviewed, with emphasis given to theoretical interpretation of the observed events. The galactic and extragalactic origin, in case of astrophysical sources of UHE particles, have the problems either with acceleration to the observed energies or with the fluxes and spectra. Topological defects can naturally produce particles with energies as observed and much higher, but in most cases fail to produce the observed fluxes. Cosmic necklaces and monopole-antimonopole pairs are identified as most plausible sources, which can provide the observed flux and spectrum. The relic superheavy particles are shown to be clustering in the Galactic halo, producing UHECR without Greisen-Zatsepin-Kuzmin cutoff. The Lightest Supersymmetric Particles are discussed as UHE carriers in the Universe.     

Normal Unenhanced Raman Spectra of CO and CH4 Adsorbed on Cobalt(poly)

Abstract

Normal unenhanced Raman spectra (NURS) of low-polarizability CO molecules were observed for the first time on cobalt at R. T. and residual gas pressure. We assign five bands observed between 2030–2130 cm^?1 to linear chemisorbed CO species, while those observed between 1840–2010 cm^?1 have been ascribed to the 2-fold chemisorbed species. The three bands observed between 1740–1830 cm^?1 we believe are due to the 3-fold species. The corresponding fourteen Co-C stretches were observed and assigned. A model based upon electron backdonation is proposed for each of the three structures. NURS were also observed at R. T. for physisorbed CH₄ and assignments are made to the four frequencies of CH_4.     

TL response of a natural fluorite

A batch of a naturally occurring fluorite (CaF₂) from the Middle Benue Valley region of Nigeria has been studied in some detail for its thermoluminescence (TL) properties. TL glow peaks are observed at 119, 144 and 224°C at a heating rate of 10°C s⁻¹. The TL response is observed to increase with increasing dose, as expected, over the dose range examined. Variations are observed in the decay curves of the various glow peaks with storage at room temperature. While the lower temperature peaks are observed to decay, enhancement of the TL signal is observed for the 224°C glow peak when stored for four weeks. A low-level radioactivity measurement showed no evidence of self-irradiation from naturally occurring radionuclides. UV exposure was suppressed by storage in a black sealed container to exclude sunlight contribution to the observed TL response. A scheme involving the formation of large defect complexes, from smaller ones, during storage, as possible route leading to loss of signal in low temperature glow peaks and a corresponding enhancement at higher temperature, is suggested.     

LDS751染料的受激喇曼散射

报道了用532nm激光抽运LDS751染料产生720—780nm可调谐染料激光输出的同时,观察到喇曼频移为102和45cm-1的反斯托克斯线,前者谱线较强,后者较弱.与这两条强线对应的斯托克斯线未能观察到.另外,还观察到喇曼频移为34cm-1的一级和二级斯托克斯线与反斯托克斯线 关键词： LDS751染料 受激喇曼散射 喇曼位移 斯托克斯线 反斯托克斯线     

High resolution x-ray study of microstructural changes in semiconductors and insulators subject to high electric fields

Using a high-resolution X-ray diffractometer, microstructural changes have been observed in Si-, LiF- and CdS-crystals subject to high d.c. and a.c. fields. At high fields the diffraction peaks are unstable due to inhomogeneous distribution of the electric current in the specimen. The inhomogeneous regions have been directly observed in high-resolution topographs. A correlation between current fluctuations and the diffracted beam intensity has been observed. Changes in peak shapes as a result of field have been observed.     

Observing Nanometre Scale Particles with Light Scattering for Manipulation Using Optical Tweezers

Nanometre-scale particles can be manipulated using optical tweezers, but cannot be directly observed. We present a simple method that nanoparticles can be directly observed using optical tweezers combined with dark field microscopy. A laser beam perpendicular to a tightly focused laser beam for trap illuminates specimen and does not enter objective, nanoparticles in focal plane all can be directly observed in dark field because of light scattering. It is implemented that the polystyrene beads of diameter lOOnm can be directly observed and trapped.     

Electroluminescence from modulation-doped pseudomorphic AlGaAs/InGaAs/GaAs quantum wells

Low-temperature electroluminescence (EL) is observed in n-type modulation-doped AlGaAs/InGaAs/GaAs quantum well samples by applying a positive voltage between the semitransparent Au gate and alloyed Au-Ge Ohmic contacts made on the top surface of the samples. We attribute impact ionization in the InGaAs QW to the observed EL from the samples. A redshift in the EL spectra is observed with increasing gate bias. The observed redshift in the EL spectra is attributed to the band gap renormalization due to many-body effects and quantum-confined Stark effect.     

Shadow images and observed luminosity of the Bardeen black hole surrounded by different accretions

In this paper, by exploring photon motion in the region near a Bardeen black hole, we studied the shadow and observed properties of the black hole surrounded by various accretion models. We analyzed the changes in shadow imaging and observed luminosity when the relevant physical parameters are changed. For the different spherical accretion backgrounds, we find that the radius of shadow and the position of the photon sphere do not change, but the observed intensity of shadow in the infalling accretion model is significantly lower than that in the static case. We also studied the contribution of the photon rings, lensing rings and direct emission to the total observed flux when the black hole is surrounded by an optically thin disk accretion. Under the different forms of the emission modes, the results show that the observed brightness is mainly determined by direct emission, while the lensing rings will provide a small part of the observed flux, and the flux provided by the photon ring is negligible. By comparing our results with the Schwarzschild spacetime, we find that the existence or change of relevant status parameters will greatly affect the shape and observed intensity of the black hole shadow. These results support the theory that the change of state parameter will affect the spacetime structure, thus affecting the observed features of black hole shadows.