Determination of the thickness of a gold layer deposited onto silicon via reflected electron spectroscopy

The energy spectra of electrons reflected from a gold layer deposited onto a silicon substrate have been measured when the energy losses are comparable with the energy of a probe electron beam (5 keV) and the elastic energy losses correspond to an electron-beam energy of 14 keV. A subsequent theory for calculating the energy spectra of electrons and light ions reflected from a multilayer target, which is used to interpret the energy spectra measured in the wide range of energy losses, has been developed. It is found that the elastic scattering processes in the gold layer (the thickness of which is tens of monolayers) substantially affect formation of the energy spectra. The Au layer thicknesses calculated by means of the developed theory are compared with those determined from the spectra of elastically reflected electrons. The errors of the Au layer thickness measurements via the proposed method are discussed.     

The radiation impedance and the energy partition among wave fields generated by a normal force strip radiator on isotropic solid surface

I.IntroductionTheacousticbeams'f0cusingandscanninggeneratedbytransducerarraysonso1idsurfacep1ayaveryimportantroleinacousticimagingandultrasonoc1ectronicdevices.InourpreviouSworkt'-'],weinvestigatcdtheproperties0ftheacousticbeams'focusingandscanninga1ongthesymmetricalaxis,acousticfic1ddistributioninthewho1espaceandnearthefocus.Andwealsogaverigoroustheoretica1ana1ysis,numcrica1simu1ationandexperimenta1obscrvation.Butra-diationimpedanceandenergyofthesurfaceradiatorshavenotbeendiscussedyetbynow.…     

Radiative energy transfer I. General equations

A set of equations is derived which makes possible to study the radiative energy transfer process whereby the photons emitted by the energy donor are absorbed by the energy acceptor and so increase the efficiency of the overall energy transfer. It is shown that the coefficients describing the radiative transfer which appear in the expressions for the intensities of the energy donor and the energy acceptor are not the same, due to the fact that part of the fluorescence absorbed by the acceptor comes from radiation which is not detected as donor emission when there is no acceptor present. The general equations derived are applied to two particular cases commonly considered: measurements in reflection, where the fluorescence emission is observed from the same face of the absorption and measurements in transmission where the fluorescence emission is observed from the opposite face of the cell.     

超短脉冲超强激光与固体靶相互作用中高能离子的产生

 用2D3V PIC粒子模拟方法得到了超短脉冲超强激光与固体靶相互作用中高能离子产生的图像，并对其机理进行了研究。在靶前后表面都观察到了高能离子的产生，并诊断了离子能谱。模拟结果表明，在靶前表面所产生的高能离子，角分布较大，在向靶内输运过程中会损失能量；在靶后表面产生的高能离子，定向性很好，能获得很高的能量。模拟得到的离子能量和实验观测结果在量级上相符。     

高能脉冲X射线能谱测量

给出了高能脉冲X射线能谱测量的基本原理及实验结果.采用Monte-Carlo程序计算了高能光子在能谱仪中每个灵敏单元内的能量沉积,利用能谱仪测量了"强光Ⅰ号"加速器产生的高能脉冲X射线不同衰减程度下的强度,求解得到了具有时间分辨的高能脉冲X射线能谱,时间跨度57ns,时间步长5ns,光子的最高能量3.0MeV,平均能量1.04MeV,能量在0.2—0.9MeV之间的光子数目最多,占46.5%.也利用二极管的电压电流波形理论计算了光子的能谱,并与利用能谱仪测得的能谱进行了比较,两种方法所得结果基本一致.     

THE STUDIES FOR ADJUSTABLE ENERGY OF PROTON BEAMS FROM PROTON LINEAR ACCELERATOR

In this paper, the principle of adjusting the proton energy from the linear accelerator with energy adjusting cavities is proposed. The requirements to energy adjusting cavities for tuning the proton energy efficiently and continually are studied. The energy range adjustable and the energy spread are calculated for 35 MeV proton linac which is in the course of construction at the Institute of High Energy Physics, as an example. The energy spread as a function of electric parameters of energy adjusting cavities are also discussed. A specific and economical method to supply rf power to energy adjusting cavities is presented.     

120~430 MeV/u 碳离子的微剂量学特性研究(英文)

单粒子微剂量谱在放射治疗中是一个极其重要的参数,它可以用来评估辐射场的生物学效应。利用蒙特卡洛程序FLUKA模拟计算了由碳离子产生的混合辐射场能量沉积的微观模式。从已公开发表的文献中选取了实验测量300 MeV/u 碳离子的线能能谱,并与相同物理条件下模拟计算得到的线能能谱相比较,结果吻合得很好。此外,还计算了120~430 MeV/u 的碳离子的剂量平均线能能谱、频率平均线能和剂量平均线能。所得到的频率平均线能值为185~ 28.3 keV/m而剂量平均线能值则为272~ 64.1 keV/m。本文的结果对于制定碳离子放射治疗的治疗计划有着重要的意义.Microdosimetric single event spectrum is a significant parameter in radiotherapy, which can be used to evaluate the radiation biological effect. In this paper, microscopic patterns of energy deposition are simulated with Monte Carlo code FLUKA at mixed radiation fields during carbon ions therapy. The results are compared with experimental measured results at 300 MeV/u carbon ion and good agreement has been found. Meanwhile, dose-weighted lineal energy spectra, frequency averaged lineal energy values and dose averaged lineal energy values of carbon ion with energy from 120 to 430 MeV/u were calculated,too. The frequency averaged lineal energy values are from 185 to 28.3 keV/m while the dose averaged lineal energy values are from 272 to 64.1 keV/m. These studies are useful for treatment plan in carbon ion radiotherapy.     

Specular and diffuse reflections of rays in coupled thin plates at high frequencies

The flexural energy distribution in two right-angled point-excited thin plates at high frequencies is investigated by means of an integral energy flow approach. The fields of energy averaged over time and frequency are described by the superposition of uncorrelated cylindrical waves stemming from both boundaries and direct sources. Specular and diffuse laws are considered for the reflection and transmission of rays, giving rise to two kinds of energy equations. The diffuse law leads to a Fredholm integral equation over the boundary sources while the specular law is shown to allow an image source solution when the plates have identical propagation properties. The algorithm for computing the image position, magnitude and directivities is described. Then, some comparisons between the results from the both energy formulations and also from the statistical energy analysis and the numerical solution of the equations of motion are performed with two damped plates at high frequency. The non-diffuse pattern of the averaged flexural energy fields is well described by the energy flow approaches.     

Energieverlustmessungen mit 60 keV Elektronen an amorphem und polykristallinem Selen und Tellur und Bestimmung optischer Konstanten

The energy loss functions Im—(1/?) of amorphous and polycrystalline Selenium and Tellurium are determined from energy loss spectra of 60 keV electrons in the energy range up to 30 eV. The optical constants ?₁ and ?₂ are calculated from the energy loss function by Kramers Kronig analysis. The energy difference in the position of the volume plasma loss of amorphous and polycrystalline foils is compared with the calculated change in free electron plasma energy resulting from density change. Characteristic structure dependence of the optical constants are found to be similar for Selenium and Tellurium. They are discussed in terms of the results of band structure calculations.     

The nuclear symmetry energy from relativistic Brueckner-Hartree-Fock model

The microscopic mechanisms of the symmetry energy in nuclear matter are investigated in the framework of the relativistic Brueckner-Hartree-Fock (RBHF) model with a high-precision realistic nuclear potential, pvCDBonn A. The kinetic energy and potential contributions to symmetry energy are decomposed. They are explicitly expressed by the nucleon self-energies, which are obtained through projecting the G-matrices from the RBHF model into the terms of Lorentz covariants. The nuclear medium effects on the nucleon self-energy and nucleon-nucleon interaction in symmetry energy are discussed by comparing the results from the RBHF model and those from Hartree-Fock and relativistic Hartree-Fock models. It is found that the nucleon self-energy including the nuclear medium effect on the single-nucleon wave function provides a largely positive contribution to the symmetry energy, while the nuclear medium effect on the nucleon-nucleon interaction, i.e., the effective G-matrices provides a negative contribution. The tensor force plays an essential role in the symmetry energy around the density. The scalar and vector covariant amplitudes of nucleon-nucleon interaction dominate the potential component of the symmetry energy. Furthermore, the isoscalar and isovector terms in the optical potential are extracted from the RBHF model. The isoscalar part is consistent with the results from the analysis of global optical potential, while the isovector one has obvious differences at higher incident energy due to the relativistic effect.     

中子在大气中产生氮俘获γ的蒙特卡罗模拟研究

为了精确计算早期核辐射,建立了中子及次级γ在大气中输运的蒙特卡罗计算模型,并利用几何分裂算法与时间分裂算法等减方差技巧提高计算效率,计算得到了距源点不同距离球面上中子与中子次级γ的信息,给出了不同位置不同时间的氮俘获γ能量释放率。开展了氮俘获γ能量释放率的规律性研究,并分析了中子能量对氮俘获γ的影响。结果表明,氮俘获γ能量释放率先随源点的距离增加而增大,在距源点约500 m达到峰值,而后随距离增加指数衰减。氮俘获γ能量释放率在时间上服从指数衰减规律,衰减时间在0.1 s左右。引入表征氮俘获γ辐射强度参数a和特征衰减时间参数τ,拟合得到了不同距离不同时间氮俘获γ能量释放率的快速计算公式。研究表明,氮俘获γ辐射强度、衰减时间及其空间分布均与中子能量密切相关。     

Broadband spectral conversion due to cooperative and phonon-assistant energy transfer from ZnO to Yb3+

The broadband spectral conversion from near-UV absorption into near-infrared emission around 1???m is reported in the ZnO?CLiYbO₂ hybrid phosphor, which is the benefit from the efficient energy transfer from ZnO to the Yb³⁺ ions that are specifically located at the interfacial diffusion regions between ZnO and LiYbO₂, rather than those in LiYbO₂ crystals. The Li⁺-related and Yb³⁺-related defect energy levels are formed inside the ZnO band gap in the ZnO?CLiYbO₂ hybrid phosphor; the former act as the quenching centers for the excitons in ZnO and meanwhile the efficient energy donors for Yb³⁺ ions, and the latter are responsible for the red shift of ZnO visible emission when the excitation energy is lower than E _g. The excitation power dependence of Yb³⁺ emission intensities is measured to investigate the number of photons that are involved in the energy transfer process, which reveals that there are two channels for the sensitizing of Yb³⁺: One is due to the energy transfer by the recombination of electrons and holes, which is a cooperative energy transfer process, and the other is via the energy feeding from the Li⁺-related energy levels, which is a phonon-assistant energy transfer process.     

Radiative energy transfer II. The effect of radiative transfer on the monomer to excimer ratio in a binary system

The equations derived in part I of this series to obtain the correction for radiative energy transfer when the observation of the fluorescence emission is made from the same face of the cell where excitation takes place are applied to the case where pyrene (Py) is the energy donor and 9,10-diphenylanthracene (DPA) is the energy acceptor. It is shown that the magnitude of the correction is quite large and that to neglect it could lead to important errors, when analysing the results regarding the possibility of a nonradiative energy transfer from Py excimers. Different methods of correcting the overall energy transfer efficiencies already published are critically reviewed.     

Calibration of centre-of-mass energies at LEP1 for precise measurements of Z properties

The determination of the centre-of-mass energies from the LEP1 data for 1993, 1994 and 1995 is presented. Accurate knowledge of these energies is crucial in the measurement of the Z resonance parameters. The improved understanding of the LEP energy behaviour accumulated during the 1995 energy scan is detailed, while the 1993 and 1994 measurements are revised. For 1993 these supersede the previously published values. Additional instrumentation has allowed the detection of an unexpectedly large energy rise during physics fills. This new effect is accommodated in the modelling of the beam-energy in 1995 and propagated to the 1993 and 1994 energies. New results are reported on the magnet temperature behaviour which constitutes one of the major corrections to the average LEP energy. The 1995 energy scan took place in conditions very different from the previous years. In particular the interaction-point specific corrections to the centre-of-mass energy in 1995 are more complicated than previously: these arise from the modified radiofrequency-system configuration and from opposite-sign vertical dispersion induced by the bunch-train mode of LEP operation. Finally an improved evaluation of the LEP centre-of-mass energy spread is presented. This significantly improves the precision on the Z width. Received: 25 March 1998 / Revised version: 3 August 1998 / Published online: 29 October 1998     

A direct transmissibility formulation for experimental statistical energy analysis with no input power measurements

An experimental statistical energy analysis method is proposed that requires neither input power measurements nor strong restrictive hypothesis on the nature of coupling between subsystems. Coupling loss factors are obtained from direct or blocked energy transmissibilities provided that total or internal loss factors are known, for instance, from application of the energy decay rate method. In turn, direct transmissibilities are computed from standard measurable energy transmissibilities, following the ideas of the direct transfer approach to transmission path analysis. The theoretical background of the proposed formulation is presented together with a numerical example to indicate how it could be applied in a practical case.     

Bipolaron in a quasi-0D quantum dot

Bipolaron states in a quasi-0D quantum dot with a spherical parabolic confinement potential are investigated by applying the Feynman variational principle. The bipolaron coupling energy and self-action potential energy are found to increase with an increase in the Fröhlich electron–phonon-coupling constant. There is also a non-monotonic dependence of the bipolaron coupling energy on the quantum dot radius. With decreasing structure radius the bipolaron coupling energy increases. However, from a critical radius it starts decreasing as the radius decreases, due to the dominance of the coulomb-to-phonon mediated interaction. When electrons in the bipolaron are forcefully neighboured, the polarization of the structure is intensified and consequently there is Coulomb repulsion. The possibility of bipolaron formation depends on the strength of the direct Coulomb repulsion which, in turn, depends on the quantum dot radius. The main contribution to the bipolaron coupling energy comes from the self-action potential. This self-action potential energy influences the energy state of the bipolaron considerably. The ratio of optical-to-static dielectric constants significantly affects the bipolaron coupling energy.     

光谱法测HT-7托卡马克诊断中性束的束成分

 实验测量了诊断中性束(DNB)中H0的4种主要能量成分(全能量，半能量，1/3能量，1/18能量)，运用光谱法来分析中性束的束成分所占百分数。根据多普勒效应，中性束中的氢粒子发出的Ha波长偏离本底的Ha波长，波长偏移量与氢粒子的能量相关，从而在光谱仪上得到多峰Ha谱线。通过编写程序并以此对实验的原始谱线进行了初步和精确拟合，最终准确有效地分析出中性束的束成分和束能量。实验测得DNB束流的中性氢粒子的全能量、半能量、1/3能量和1/18能量4种成分分别占15%,42%,35%,8%。     

A new energy source originating from extra dimensions

In this work the Einstein gravitational field equations and the Lichnerowicz boundary formalism in the extra dimensions are used to build up our black hole model from 6-dimensional space－time. From the internal stress－energy tensor the solutions with energy levels and semiclassical space-quantization are obtained, which combines with only one metric condition outside the defect. We show a new type of energy source, which originates from extra dimensions. A part of the energy source of quasi-stellar object (QSO) maybe come from extra dimensions in that way. The theoretical arithmetic upper limit is identical to that of the output energy of QSO.     

Angular and energy distributions of low energy electrons from backscattered-conversion electron Mössbauer spectroscopy

Angular and energy distributions of backscattered-low energy resonant and nonresonant electrons from iron films are studied both theoretically and experimentally. The results indicate that relatively few emerging resonant or nonresonant electrons are observed/predicted between 600 eV and 50 eV kinetic energy. A significant fraction of the total electron signal emerges, however, below 50 eV, which is shown to result from low energy Auger cascades, low energy shake-off electrons and secondary electrons attributed to higher energy events. The large number of low energy electrons permits relatively short acquisition times (ca. 1h) and enhanced surface sensitivities. They may be especially useful in future depth-deconvolution efforts.     

Ion temperature and hydrodynamic-energy measurements in a Z-pinch plasma at stagnation

The time history of the local ion kinetic energy in a stagnating plasma was determined from Doppler-dominated line shapes. Using independent determination of the plasma properties for the same plasma region, the data allowed for inferring the time-dependent ion temperature, and for discriminating the temperature from the total ion kinetic energy. It is found that throughout most of the stagnation period the ion thermal energy constitutes a small fraction of the total ion kinetic energy; the latter is dominated by hydrodynamic motion. Both the ion hydrodynamic and thermal energies are observed to decrease to the electron thermal energy by the end of the stagnation period. It is confirmed that the total ion kinetic energy available at the stagnating plasma and the total radiation emitted are in balance, as obtained in our previous experiment. The dissipation time of the hydrodynamic energy thus appears to determine the duration (and power) of the K emission.