X射线屏的理论效率和实验效率

作者计算了新、老X射线磷光体屏的射线检测理论效率。对于给定的X射线能量来说,X射线量子检测效率定义如下: QDE_E=A_E·η·λ_(Em)·C_E·Dλ     

Reduction of PDF uncertainty in the measurement of the weak mixing angle at the ATLAS experiment

We investigate the parton distribution function(PDF) uncertainty in the measurement of the effective weak mixing angle sin ~2θ_(eff)~l at the CERN Large Hadron Collider(LHC).The PDF-induced uncertainty is large in proton-proton collisions at the LHC due to the dilution effect.The measurement of the Drell-Yan forward-backward asymmetry(AFB) at the LHC can be used to reduce the PDF uncertainty in the sin~2θ_(eff)~l measurement.However,when including the full mass range of lepton pairs in the A_(FB) data analysis,the correlation between the PDF updating procedure and the sin~2θ_(eff)~l extraction leads to a sizable bias in the obtained sin ~2θ_(eff)~l value.From our studies,we find that the bias can be significantly reduced by removing Drell-Yan events with invariant mass around the Z-pole region,while most of the sensitivity in reducing the PDF uncertainty remains.Furthermore,the lepton charge asymmetry in the Wboson events as a function of the rapidity of the charged leptons,A_±(η_l),is known to be another observable which can be used to reduce the PDF uncertainty in the sin~2θ_(eff)~l measurement.The constraint from A_±(η_l)is complementary to that from A_(FB),and thus no bias affects the sin~2θ_(eff)~l extraction.The studies are performed using the error PDF Updating Method Package(ePump),which is based on Hessian updating methods.In this article,the CT14 HERA2 PDF set is used as an example.     

用Judd-Ofelt理论计算YAG:Er~(3 )晶体中Er~(3 )的光谱参数

本工作根据Jndd-Ofelt理论,利用28个吸收光谱支项,19组方程计算了实验与理论振子强度,均方根偏差仅为1.9×10~(-7).用最小二乘法拟合实验与理论振子强度所得到的三个Ω_λ唯像强度参数为:Ω_2-0.19×10~(20)cm~2;Ω_4=1.68×10~(-20)cm~2;Ω_6=0.62×10~(-2)cm~2.然后,计算了自发辐射电偶和磁偶跃迁几率,辐射寿命,荧光分支比与各激发态的辐射电偶和磁偶振子强度.并示出了0.3～0.2μm波段内的荧光光谱.     

~(12)C离子引起裂变反应的碎片角分布

本工作采用固体核径迹探测器(天然白云母)和金硅面垒型半导体器测量了72.7,69.6,67.4,65.4,63.4和61.4MeV~(12)C离子轰击~(169)Tm,~(175)Lu,~(181)Ta,W,Re,pt,~(197)Au,Pb和~(209)Bi裂变反应的碎片角分布.建立在鞍点模型基础上的裂变碎片角分布理论能够很好地解释碎片角分布实验数据.对于不同的可裂变参数Z~2/A,本工作给出了K_0~2随核激发能E的变化趋势.由碎片角分布各向异性提取的(?)_0/(?)_(eff)值与转动液滴模型的计算值做了比较.     

α-蒎稀光电离和离解动力学的同步辐射研究（英文）

为研究α-蒎稀的光电离解离机制,采用同步辐射光电离质谱,在7.9~15.5 e V能量范围内研究了α-蒎稀的紫外光电离解离,对α-蒎稀的电离解离能及其碎片离子的出现势进行了理论分析.实验测得光电离效率曲线,从光电离效率曲线中获得α-蒎稀C_(10)H_(16)的电离能和碎片离子C_9H~+_(13),C_7H~+_(10),C_3H_6~+及CHH_3~+的出现势.用Gaussian 03理论方法计算了C_(10)H_(16)和主要的光解离碎片的总能量,用高级能量计算方法计算了C_(10)H_(16)的电离能和部分碎片离子的出现势及主要的解离通道的离解能.根据实验和理论计算结果,分析了产生碎片离子的主要的解离通道.分析表明实验测得的结果与理论计算提出的C_(10)H_(16)的光解离通道获得的解离能符合得较好.     

Er_xY_(1-x)Al_3(BO_3)_4晶体的生长和光谱性质

采用助熔剂法生长出了掺杂均匀的Er_xY_(1-X)Al_3(BO_3)_4厘米级优质单晶.测定了晶体的吸收、激发光谱.用Judd_Ofelt理论计算了晶体中Er~(3+)的十一条谱带的振子强度(ρ_(ad)和ρ_(md)以及Er~(3+)的强度参数Q_λ(λ-2、4、6).并由此计算了Er~(3+)不同能级之间跃迁的爱因斯坦自发辐射系数A_r、辐射寿命r、荧光分支比β_3以及积分发射截面Σ.根据这些参数讨论了在EYAB晶体中可能实现激光输出的通道.     

Measurements of effective delayed neutron fraction in a fast neutron reactor using the perturbation method

A perturbation method is proposed to obtain the effective delayed neutron fraction β_(eff) of a cylindrical highly enriched uranium reactor.Based on reactivity measurements with and without a sample at a specified position using the positive period technique,the reactor reactivity perturbation △ρ of the sample in β_(eff) units is measured.Simulations of the perturbation experiments are performed using the MCNP program.The PERT card is used to provide the difference dκ of effective neutron multiplication factors with and without the sample inside the reactor.Based on the relationship between the effective multiplication factor and the reactivity,the equation β~(eff)=dκ/△ρ is derived.In this paper,the reactivity perturbations of 13 metal samples at the designable position of the reactor are measured and calculated.The average β_(eff) value of the reactor is given as 0.00645,and the standard uncertainty is 3.0%.Additionally,the perturbation experiments for β_(eff) can be used to evaluate the reliabilities of the delayed neutron parameters.This work shows that the delayed neutron data of ~(235)U and ~(238)U from G.R.Keepin's publication are more reliable than those from ENDF-B6.0.ENDF-B7.0,JENDL3.3 and CENDL2.2.     

A型超导体的近似临界温度公式(Ⅰ)μ~*=0情形

本文用数值解方法从Eliashberg方程计算出超导临界温度T_c,并考察T_c对有效声子谱的依赖关系。在这个研究中,a~2F(ω)被取为双δ函数谱,并允许其中的谱参数可以在很宽范围内改变。作者发现在λ<∧区域(即在T_c级数解的收敛圆外),T_c除了依赖λ和矩比外,还依赖T_c级数解的收敛半径倒数Λ;它们之间的关系是有规律的。在这些结果的启示下,本文在μ=0情形,用弥合数值解的方法得到一个适用于λ<Λ区域的T_c近似公式。 接着,本文作者对吉光达和吴杭生的一篇文章进行了研究,指出:该文提出的超导体分类建议及其工作的主要结论是对的。但其中对决定A型超导体临界温度主要参量问题进行的分析,只适用于这样一些A型超导体,它们的收敛半径倒数Λ或者比λ_0小,或者虽比λ_0大、但λ又小于λ_0,其中λ_0是个依赖谱形状的参量,它的定义在正文中给出。对另一些A型超导体(λ_0<λ<Λ),决定T_c的主要参量不再是λ,而是δ=1/∧~(0.5)(_(1/2)/ω_(log))~(5.5)λ~(1.55)。     

燃料电池系统最大热力学电效率及对氢气、甲烷和丙烷的应用结果（英文）

燃料电池系统的最大电效率(η_e~(max))对理解和发展燃料电池技术至关重要.本文通过对燃料电池系统的热力学分析,在考虑加热燃料与空气至燃料电池工作温度的热量需求的基础上,建立了燃料电池运行过程的能量平衡关系,进而推导出了η_e~(max)的显式理论表达式.结果表明,与卡诺效率不同,η_e~(max)与燃料有关.由于除氢燃料外,计算η_e~(max)需要进行化学平衡计算,本文推导了烷烃燃料化学平衡态的解析解.所得理论模型被用于分析温度(T)与燃料水含量及废热回收率对η_e~(max)的影响.结果表明,甲烷和丙烷燃料的η_e~(max)随温度的升高而显著降低.此外,对中等废热回收率且运行于700℃≤T≤900℃的燃料电池系统,氢气燃料的η_e~(max)要高于甲烷和丙烷燃料的η_e~(max).     

EXPERIMENTAL TESTS OF GRAVITATIONAL THEORY

<正>Revised September 2013 by T.Damour(IHES,Bures-sur-Yvette,France).Einstein's General Relativity,the current"standard'theory of gravitation,describes gravity as a universal deformation of the Minkowski metric:gμv(x~λ)=η_(μv)+h_(μv)(x~λ),whereη_(μv)=diag(-l,+l,+l,+l).(21.1)General Relativity is classically defined by two postulates.One postulate states that the Lagrangian density describing the propagation and self-interaction of the gravitational field is     

Calculation algorithm of high-precision two-dimensional broadband laser warning parameters北大核心CSCD

High precision grating diffraction laser warning system is a photoelectric countermeasure equipment to judge and locate the incoming laser function. In order to improve the positioning accuracy, an improved algorithm for calculating and fitting the calculation parameters of the spot center was proposed. Firstly, the laser spot was preprocessed, and the center coordinates of the connected area were obtained by using the improved connected area marking algorithm and spot center extraction algorithm. Secondly, the azimuth angle and pitch angle were set, the images were collected and the spot center was calculated, and the pixel horizontal and vertical coordinates in x and y direction as well as fitting surfaces of laser parameters were fitted, so as to judge the azimuth angle, pitch angle and wavelength of the incoming laser. Finally, the improved connected area marking algorithm, spot center extraction algorithm and parameter fitting calculation results were compared with the traditional algorithm. The experimental results show that the pitch angle error between the fitting calculation results and the real data is less than 0.4°, and the azimuth angle error is less than 0.2°, which greatly improves the accuracy of laser direction recognition. Copyright ©2022 Journal of Applied Optics. All rights reserved.     

A study of antineutrino spectra from spent nuclear fuel at Daya Bay

The Daya Bay Reactor Antineutrino Experiment is designed to determine the as yet unknown neutrino mixing angle, θ₁₃, by measuring the disappearance of electron antineutrinos from several nuclear reactor cores. The projected sensitivity in sin²(2θ₁₃) of better than 0.01 at a 90% CL should be achieved after three years of data-taking. Antineutrinos emitted from spent nuclear fuel (SNF) distort the soft part of the energy spectrum. In this article, a calculation of the antineutrino spectra from the long-life isotopes in SNF is performed. A non-equilibrium generation of long half-life isotopes during the running time of the reactor is also analyzed. Finally, we show that the antineutrino event rate contribution from SNF, which has been stored in the SNF pool for several years, may be non-negligible.     

Theoretical investigation of the electronic structure of a ferroelectric SbSI cluster at a phase transition

This paper presents the theoretical investigation of energy levels of valence bands (VB) and core levels (CL) of the ferroelectric SbSl single crystals in antiferroelectric and ferroelectric phases. Since the best approximation for the deep VB levels is a calculation by the Hartree-Fock method, the molecular model of a SbSI crystal was used for calculations. This model of the crystal was also used for calculations of the total density of states. It was found that the VB and CL of this ferroelectric semiconductor are sensitive to the small lattice distortion at the phase transition, and that an average of the total density of states, when all atoms participate in oscillations of all normal modes, are more similar to the experimental X-ray photoelectron spectra (XPS). The experimental splitting of CL obtained by XPS was compared with the theoretically calculated one by two different methods. The cluster model calculations showed that the splitting of the CL in SbSI might be caused by photoelectron emission from the atoms, which have different valence state, at the surface.     

五棱镜转动时出射光角度的变化

为了对大口径平面镜面形轮廓的五棱镜扫描法测试进行误差分析和修正,对五棱镜转动时出射光角度的变化进行了分析与精确计算。首先建立了合适的坐标系并规定了角度的正负,然后由入射光的偏摆角和俯仰角计算入射光向量,接着介绍了五棱镜的作用矩阵与坐标转换矩阵,在此基础上详细分析了五棱镜转动的整个过程并且计算了出射光向量。然后计算出射光的偏摆角和俯仰角,再计算当五棱镜没有转动时出射光的偏摆角和俯仰角。最后计算出射光偏摆角和俯仰角的变化。特别分析了当入射光垂直入射五棱镜的情况。随后进行了实际计算与实验,总结了出射光角度变化的一些规律。将计算数据与实验数据进行了比较,结果最大偏差为1"。最大偏差在实验精度范围内,证明了计算方法是正确的。     

Auger electron/X-ray photoelectron and cathodoluminescent spectroscopic studies of pulsed laser ablated SrAl2O4:Eu,Dy thin films

Auger electron/X-ray photoelectron and cathodoluminescent (CL) spectroscopic studies were conducted on pulsed laser deposited SrAl₂O₄:Eu²⁺,Dy³⁺ thin films and the correlation between the surface chemical reactions and the decrease in the CL intensity was determined. The Auger electron and the CL data were collected simultaneously in a vacuum chamber either maintained at base pressure or backfilled with oxygen gas. The data were collected when the films were irradiated for 14 h with 2 keV electrons. The CL emission peak attributed to the 4f⁶5d¹ → 4f⁷ transitions was observed at ∼521 nm and the CL intensity of the peaks degraded at different rates in different vacuum conditions. X-ray photoelectron spectroscopy (XPS) data collected from degraded films suggest that strontium oxide (SrO) and aliminium oxide (Al₂O₃) were formed on the surface of the film as a result of electron stimulated surface chemical reaction (ESSCR).     

Synchrotron radiation computed laminography using an inclined detector

Synchrotron radiation computed laminography (SR‐CL) has been in use in three‐dimensional non‐destructive imaging of flat objects for several years. A new set‐up is proposed based on the traditional SR‐CL method but with the detector inclined at the same angle as the sample inclination to collect projections. The results of computer simulations and real‐sample experiments demonstrate that reconstructions acquired using an inclined detector are of better quality compared with those acquired using ordinary detecting methods, especially for the situation of few projections and small difference of attenuation ratio of the sample. This method could be applied to obtain high‐quality images of weak‐contrast samples with short measurement time and mild radiation damage.     

铅球最佳投掷角的精确方程及数值解

指出关于铅球最佳投掷角计算公式中存在的问题,提出了计算这一角度的精确方程和数值解。     

Search for {\rm B_s}^0 oscillations using inclusive lepton events

A search for oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991–95. Compared to previous inclusive lepton analyses, the proper time resolution and b-flavour mistag rate are significantly improved. Additional sensitivity to mixing is obtained by identifying subsamples of events having a purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed to derive a lower limit of at the 95% confidence limit (95% CL). Combining with the ALEPH -based analyses yields at 95% CL. Received: 20 July 1998 / Published online: 19 February 1999     

Regge closed string scattering and its implication on fixed angle closed string scattering

We calculate the complete closed string high energy scattering amplitudes (HSA) in the Regge regime for arbitrary mass levels. As an application, we deduce the complete ratios among closed string HSA in the fixed angle regime by using Stirling number identities. These results are in contrast with the incomplete set of closed string HSA in the fixed angle regime calculated previously. The complete forms of the fixed angle amplitudes, and hence the ratios, were not calculable previously without the input of zero-norm state calculation. This is mainly due to the lack of saddle point in the fixed angle closed string calculation.     

MOLECULAR DYNAMICS SIMULATION ON LOW ANGLE GRAIN BOUNDARIES

Molecular dynamics simulation has been performed to investigate the microstructure and properties of low angle grain boundaries, employing the embedded atom method(EAM) type interatomic potential for Ni-Al alloy. The energies of the low angle grain boundaries with different dislocation densities were calculated, and the results indicate that the low angle grain boundary energy varies as a function of misorientation angle. The simulation was found in good agreement with the calculation on the basis of the dislocation theories in the low angle scale. The low angle grain boundary energy goes up with the increase of misorientation angle and tends to go down after reaching a maximum. An energy cusp exists when the misorientation angle increases further, but in this scale the dislocation theories are invalid for energy calculation due to the strong interaction of the dislocations at the boundaries. The simulation results also indicate that the microstructure of low angle grain boundaries can still be described as dislocations when the misorientation angle is larger than 10°.