含单空位纯α-Zr晶体的结构、电子和能量性质的第一性原理研究

采用第一性原理方法,使用Win2k软件对含不同单空位浓度纯α-Zr体系的结构、电子和能量性质开展了研究,获得了含不同单空位浓度的纯α-Zr晶格常数的变化,并计算了其电子密度、态密度和能带结构。结果表明,随着单空位浓度的升高,纯α-Zr的晶格常数减小;当空位作为纯α-Zr晶格中Zr原子的第一近邻原子时,其电子密度在相邻Zr原子的方向上延伸,而不含空位的Zr原子的电子密度呈对称分布;随着体系空位浓度的降低,总态密度主峰升高,能带结构和费米面变得更加复杂。     

Pu-H2相互作用的反应机理及电子密度分析

通过量子力学中密度泛函理论的相关方法和相对论有效原子实模型(RECP),应用Gaussian09程序对钚与氢气的相互作用进行了计算和分析。计算得到了钚与氢气的详细微观反应机理：Pu+H2→FC→TS→PuH2,优化了沿反应路径的特殊结构（能量极小点及过渡态）,并通过能量分析画出了势能剖面图。基于优化的几何结构,通过多种拓扑分析方法分析了反应路径中所有特殊结构的电子密度相关性质,如自旋密度分析、Mulliken自旋布居分析、电子定域泛函理论分析,得到了电子密度在反应过程中的详细变化。     

中能重离子碰撞中的自旋轨道耦合

核的自旋轨道相互作用对解释原子核的幻数和壳结构十分重要。然而,一直以来,它只在核结构领域被广泛研究,在核反应过程中的效应通常被忽略。本文总结了近期第一次在描述中能重离子碰撞的IBUU(Isospin-dependent Boltzmann-Uehling-Uhlenbeck)输运模型中引入核子的自旋自由度和核自旋轨道相互作用所产生的自旋相关平均场势的研究工作。我们发现,可以利用横向自旋差分流来研究核自旋轨道耦合,中质子的自旋差分流之差可以用来研究自旋轨道耦合的同位旋依赖性,而不同束流能量下高横向动量的自旋差分流则可以用来提取自旋轨道耦合的密度依赖性。中能重离子碰撞在不久的将来有望成为研究核自旋轨道相互作用的另一条有效途径。     

PuO_2晶体结构、弹性和电子性质的第一性原理研究

采用基于密度泛函理论的全势能线性缀加平面波方法(FLAPW),在局域自旋密度近似(LSDA)和广义梯度近似(GGA)及LSDA/GGA+U(U为电子间的库仑排斥参数)下,系统研究了强关联5f电子体系PuO_2的晶体结构、电子态密度、电荷密度和弹性参数。优化计算结果表明,PuO_2的晶格参数和体变模量与实验结果吻合较好;LSDA/GGA+U使得体系从导体转变为绝缘体,与实验测定结果符合;加U后体系5f电子的定域性减弱,离域性增强,Pu—O之间有明显的成键特性。     

辐射聚合α-甲基丙烯酸的1H NMR研究

用1H NMR谱和质子自旋弛豫时间研究了γ射线辐射引发的α-甲基丙烯酸的聚合反应、其聚合转化率和聚合物链运动与吸收剂量和剂量率的关系.对比了聚合物在不同溶剂中各质子化学位移的变化.结果表明α-甲基丙烯酸聚合转化率随着吸收剂量的增加而增大,吸收剂量率则反之.从自旋-晶格弛豫时间(T1)和自旋-自旋弛豫时间(T2)测定中得知,自旋-晶格弛豫时间几乎不随剂量变化而变化.当聚合转化率较大时,聚合物链运动呈多指数弛豫特征.在重水溶剂中加入少量的氘代NaOH,不仅提高了谱图的分辨率,也使各质子化学位移发生了移动.     

奇—奇核^170Ta高自旋态及旋称反转研究

旋称反转（Signature inversion）研究是近年来奇-奇核高自旋态研究的热门课题之一。实验发现,稀土区奇-奇核普遍存在低自旋区旋称反转现象,即出现非优惠的旋称能态低于优惠旋称能态的反常能量劈裂。对这种反常现象有各种理论解释,目前仍无定论。因而,累积更多的实验成果,揭示其系统规律对澄清理论分歧是十分有益的。为此,在HI-13串列加速器上以能量为97MeV的19F束通过155Gd（19F,4n）170Ta反应研究了170Ta的高自旋态能级结构。将前人建立的3个转动带分别推向更高自旋态（图1）。在新建的能级纲图的A带中,增加了能量为311.5、319.5和680.9 keV的3条γ跃迁,并将前人结果中21-到19-的647keV     

基于β辐生伏特效应的同位素微能源研究

介绍了基于辐生伏特效应的放射性同位素微电池的理论研究,建立了p n型和n p型微电池能量转化结构的理论模型,分析了影响微电池性能的主要参数,并对两种能量转化结构的主要设计参数进行了优化.比较了p n型和n P型两种能量转化结构的性能.     

表面峰强度的Monte Carlo模拟计算

本文介绍用Monte Carlo模拟方法对入射He~+离子能量在0.1—2.OMeV范围内,硅、铝单晶在几种不同表面结构条件下的表面峰强度进行了计算。讨论了离子入射能量、入射角度、晶格原子热振动幅度、相关系数、表面增强因子、原子位移和吸附原子等因素对计算结果的影响。     

聚变堆中第一壁材料钨的紧束缚理论研究

为研究辐照时处于电子激发态下第一壁材料钨（W）的结构演化规律和热力学性质,采用紧束缚方法对聚变堆中W的物理性质进行理论研究。结果表明,体系在高能粒子辐照下诱导的电子激发导致了体系中被辐照的区域自发出现微孔、晶格急剧膨胀、熔点下降等现象。具体地,在中等电子温度（~5 000 K）以下,W的晶格膨胀主要由晶格温度驱动,但在电子温度较高时电子温度导致被辐照区域的晶格膨胀效应不可被忽略。特别是当电子温度很高（>10 000 K）时,即便晶格温度不高,电子温度也会导致很大程度晶格膨胀。这对认识聚变堆中第一壁材料W在服役过程中的物理状态十分重要。     

Wien2k电子结构计算程序及其部分应用

近年来,基于密度泛函理论的第一性原理计算方法得到了很大的发展,并被广泛应用。第一性原理的Wien2k程序用于计算键能和态密度,电子密度和自旋密度,电场梯度,超精细场,自旋极化,自旋-轨道耦合,费米面等。根据扰动角关联和角分布、β-NMR和β-NQR研究材料微观结构、磁性和电性需要计算材料的电场梯度、超精细场、自旋极化,引进了Wien2k程序。Wien2k是由Fortran90语言编写的,在UNIX系统中运行。采用Wien2k正在计算LaFeO纳米磁性材料的电场梯度和超精细场。Wien2k电子结构计算程序及其部分应用@杜恩鹏 @郑永男 @周冬梅 @袁大…     

Calculation of the field spectrometer response and calibration for the operational and accidental monitoring of nuclear power plant neighbourhood

A method and computer codes for the modelling of a field spectrometer response versus the arbitrary mixture of radionuclide activities on the ground are presented. The problem is solved in two steps:

1. 1) Monte Carlo simulation of the photon field at a given level in air above a semiinfinite source that represents contaminated ground,

2. 2) Monte Carlo modelling of the scintillation detector response in the photon field with calculated characteristics.

Calculations make it possible to construct the detector response matrix for purposes of the analysis and processing of the data from air spectrum monitoring. Results for the real detection system obtained in cooperation with Research Institute for Nuclear Power Plants in Jaslovské Bohunice are discussed.     

航空放射性测量的模拟计算

航测系统刻度主要有实验刻度法、模拟实验刻度法、Beck法和蒙特卡洛法.将模拟实验刻度法与蒙特卡洛方法结合,通过MCNP4c程序对系统进行模拟,计算不同高度下对点源的计数,并与木板模拟实验结果对比,得到航测系统在不同高度下计数率的变化规律,并计算出转换因子公式,对今后航空放射性测量高度校正的研究具有指导意义.     

X射线源针孔成像系统优化设计研究

为提高X射线源针孔成像系统的性能,对成像能区为10~100 keV的X射线源针孔成像系统进行了优化设计研究。综合应用了理论分析和蒙特卡罗模拟的方法,首先根据X射线波长、准直器角响应和X射线穿透效应对针孔成像的不同影响结果设计了可有效控制成像分辨率和成像面积变化的船底型准直器,随后用蒙特卡罗方法对使用该准直器的针孔成像系统进行了模拟验证。结果表明,对于100 keV以下的X射线,经船底型准直器后,成像的空间分辨率和亮斑亮度较稳定,能得到相对准确的X射线源定位、定量信息。     

HTR-10 full core first criticality analysis with MCNP

Experimental facilities like HTR-10, HTTR, and ASTRA serve as the source of information for the currently designed high temperature gas-cooled nuclear reactors. It is also desired to verify the existing codes against the data obtained in such facilities. In this study, first criticality calculations of a pebble bed gas-cooled reactor, HTR-10, is performed with MCNP-4B, a code system for Monte Carlo particle transport simulation. HTR-10 has rather unique characteristics in terms of the randomness in geometry as in the case of all pebble bed reactors. The geometrical model of the full reactor is obtained by using lattice and universe facilities provided by MCNP. Modeling details are discussed with necessary simplifications. Results obtained by Monte Carlo simulations are compared with available data. It is observed that Monte Carlo simulations yield sufficiently accurate results in terms of initial criticality of the HTR-10 reactor.     

离子电离与次级反应耦合的蒙特卡罗模拟方法研究与应用

氘或氚离子在靶物质中电离输运的同时会发生次级反应,为模拟这一过程,开发了耦合蒙特卡罗工具RSMC。程序用详细历史法和浓缩历史法模拟电离过程,调用ENDF或TENDL中D、T核数据计算次级反应,同时使用“强迫次级粒子产生”降方差技巧提高模拟效率。对中子深度分析问题、加速器单能中子源问题和热中子-聚变中子转换靶问题进行研究,验证了RSMC的正确性。     

Defect distribution in ion implanted silicon: comparison between Monte Carlo simulation and triple crystal X-ray measurements

Depth distributions of excess vacancies and interstitials, obtained by a Monte Carlo simulation in self-ion implanted silicon, are compared with lattice strain profiles deduced by triple crystal X-ray rocking curves.     

Monte Carlo simulation of the Greek Research Reactor neutron irradiation facilities

A Monte Carlo simulation of the Greek Research Reactor was carried out using MCNP-4C2 code and continuous energy cross-section data from ENDF/B-VI library. A detailed model of the reactor core was employed including standard and control fuel assemblies, reflectors and irradiation devices. The model predicted neutron flux distributions within the core in good agreement with calculations performed using the deterministic code CITATION and measurements using activation foils. The model is used for the prediction of the neutron field characteristics at the reactor irradiation devices and enables the design and evaluation of experiments involving material irradiations.     

过滤X射线参考辐射场特性的蒙特卡罗模拟研究及实验验证

为研究过滤X射线参考辐射场特性,利用蒙特卡罗方法对中国原子能科学研究院计量测试部过滤X射线参考辐射场的原级谱、均匀性及散射辐射进行了模拟,并利用PTW球形电离室进行了实验测量。结果表明,蒙特卡罗模拟结果与实验结果符合较好,验证了所建模型的正确性及蒙特卡罗方法对模拟过滤X射线参考辐射场的有效性,为后续模拟研究工作奠定了基础。     

Calculation of track and vertex errors for detector design studies

The Kalman filter technique has come into wide use for charged track reconstruction in high-energy physics experiments. It is also well suited for detector design studies, allowing for the efficient estimation of optimal track covariance matrices without the need of a hit level Monte Carlo simulation. Although much has been published about the Kalman filter equations, there is a lack of previous literature explaining how to implement the equations. In this paper, the operators necessary to implement the Kalman filter equations for two common detector configurations are worked out: a central detector in a uniform solenoidal magnetic field, and a fixed-target detector with no magnetic field in the region of the interactions. With the track covariance matrices in hand, vertex and invariant mass errors are readily calculable. These quantities are particularly interesting for evaluating experiments designed to study weakly decaying particles which give rise to displaced vertices. The optimal vertex errors are obtained via a constrained vertex fit. Solutions are presented to the constrained vertex problem with and without kinematic constraints. Invariant mass errors are obtained via propagation of errors; the use of vertex constrained track parameters is discussed. Many of the derivations are new or previously unpublished     

Energy-Space Dependent Error Propagation in Monte Carlo Coupling Calculation

A new formulation of energy-space dependent propagation of errors has been derived for the Monte Carlo-Monte Carlo coupling technique which is applied to analysis of radiation streaming through a long path. In this formula, it is considered that the source uncertainty due to the statistical error of the preceding Monte Carlo calculation is handed down to a particle as an uncertainty of the particle weight. In the succeeding Monte Carlo calculation, the propagated weight error is scored together with the particle weight by flux estimators. The method has been implemented in the MORSE-ALB code system. As a sample problem, calculation of reaction rates in the main pump room of the primary coolant system of JOYO is performed with the Sn-AMC-AMC coupling technique. As a result, the present method turned out to be significant in estimating the Monte Carlo statistical error of the final value taking into consideration of the energy-space dependence of error propagation.