重离子径迹模板中组装半导体CdS一维纳米材料

用重离子辐照的聚碳酸酯为模板,采用电化学沉积法制备了半导体CdS纳米线和纳米管.通过选用不同蚀刻时间的模板,得到了直径20～100 nm、长度20～30 μm范围、粗细均匀且具有纤维锌矿结构的CdS纳米线与纳米管.利用扫描电子显微镜(SEM)、X射线衍射(XRD)和透射电子显微镜(TEM)对CdS纳米线与管的形貌和晶体结构特征进行了表征.     

擦拭样品中铀微粒甄别技术的研究

基于裂变径迹原理对擦拭样品中微米量级铀微粒筛选技术进行了研究.研究内容包括擦拭样品与载体分离、样品在裂变径迹片上沉积、样品辐照以及化学刻蚀、铀微粒筛选等.文章中对各实验环节进行细致描述和讨论.研究发现:(1)以无尘滤纸、脱脂棉、Texwipe牌TX304型棉布为擦拭载体的样品经过400℃ 6 h灰化为较好的分离方法;(2)经热中子辐照和化学刻蚀后裂变径迹主要呈星状和坑状.其中235U含量高的微粒对应于坑状径迹,含量低的微粒对应于星状径迹;(3)采用新的定位方法能够筛选出铀微粒.     

低能氮离子注入香菇生物学效应的研究

本文用能量为 15 keV,而注量不同的氮离子注入对武香一号香菇进行诱变,分析了不同注量下菌丝长速,菌丝生物量以及多糖含量的变化,对该低能离子与微生物间的作用规律进行了初步探索,为进一步筛选出多糖高产菌株提供前提.实验结果表明菌丝长速,菌丝生物量及多糖含量随不同注量的变化情况基本遵循"马鞍型曲线".注量小时菌丝日均长速较快,随着注量的增大,菌丝日均长速呈下降趋势,但在1.5×1016cm-2附近,菌丝长速有短暂回升.在注量较小时,随着注量的增加,菌丝生物量及多糖含量先升高后降低,注量为4×1015cm-2时,两者均达到最大值,而后会出现小的波动,注量增加到1.5×1016cm-2时,菌丝生物量及多糖含量又会达到-个较大的峰值.通过发酵动力学分析,研究了香菇液体菌种培养过程中菌丝球数量及形态、摇瓶总重、pH值、多糖含量等指标的变化情况,绘制该菌发酵产糖的过程曲线,这将为诱变前后液体发酵过程的控制提供参数.     

放疗后早期肿瘤组织内99Tcm-rh-Annexin Ⅴ分布与Survivin、Caspase-3蛋白表达的相关性研究

采用99Tcm-rh-AnnexinⅤ作为核素凋亡显像示踪剂,观察小鼠放疗后早期肿瘤组织内Survivin、Caspase-3蛋白表达。结果显示,放疗组肿瘤组织内99Tcm-rh-AnnexinⅤ分布、TUNEL检测阳性细胞数及Caspase-3蛋白表达均明显多于对照组,Survivin蛋白表达A组明显高于B组,差异均存在显著性（P均<0.01）。相关性研究表明,肿瘤组织的放射性摄取与TUNEL阳性细胞数呈明显正相关（r=0.942,P=0.000）;肿瘤组织内Survivin蛋白表达与Caspase-3蛋白表达呈明显负相关（r=-0.836,P=0.000）。肿瘤组织内99Tcm-Annexin Ⅴ分布与Caspase-3蛋白表达呈明显正相关（r=0.948,P=0.000）,与Survivin蛋白表达呈明显负相关（r=-0.819,P<0.01）。以上结果提示,肿瘤组织内99Tcm-rh-AnnexinⅤ的分布可以反映放疗后早期肿瘤组织细胞凋亡的状况以及凋亡调控蛋白Survivin、Caspase-3表达水平的变化。     

放射治疗中肿瘤靶区勾画的主观差异性分析

为了解医生的主观因素在肿瘤靶区(GTV)勾画中产生差异性并分析其原因,对肿瘤处在身体不同部位的12例病人的CT定位图像,组织了来自放射治疗和影像诊断的6位医师进行了GTV勾画,计算病人GTV的体积值及其变化范围,比较两个学科和两次勾画所产生的差异性.结果表明,9位病人GTV体积最大值/最小值比值＜2,3位病人的项比值＞2;16%的体积值对体积平均数的变动范围＞±25%.在已知影响准确性的重要客观因素一致的条件下,造成差异性的主要原因是医生间学科的不同,影像科医生比放疗科医生的变异性小、准确性高.因此,在确定GTV时,对于因主诊医生主观因素产生的误差要引起重视,放射治疗医生加强影像诊断学知识学习与协作,建立、完善并认真执行相关的QA与QC规程是解决问题的主要方法.     

三代核电自主化依托项目的工程建造管理模式

2007年7月24日,国家核电技术公司、三门核电有限公司、山东核电有限公司、中国技术进出口总公司,与美国西屋联合体及分包商分别签订了第三代核电自主化依托项目4个机组的核岛设计及部分主设备采购合同;国家核电技术     

国外最新消息

伊朗总统宣布已开始安装6000台新离心机伊朗总统艾哈迈迪·内贾德2008年4月8日宣布,伊朗已开始在纳坦兹铀浓缩基地安装6000台新的离心机。(编译自法新社2008年4月8日报道)     

高压氘氚气氛下不锈钢吸附氚的初步研究

本工作对于氚在不锈钢表面的吸附和解吸行为进行了初步研究.样品在n(D)∶n(T)=1∶1,230℃时,15 MPa下恒温8 h后,接着在27 MPa下恒温6 h的情况下进行了氚的吸附,测量了室温下和加热到1173 K时的解吸氚量和总吸附量.其结果如下:不锈钢的总吸附氚量是857.4 MBq·cm-2,不锈钢的解吸氚量是722.2 MBq·cm-2;在本实验的条件下,在室温和加热条件下,不锈钢所释放的氚中,化学成分主要是HTO和HT两部分,大部分以HT形式存在;不锈钢的自由氚占吸附总氚量的7.34%;不锈钢的热解吸谱存在三个解吸峰,其解吸温度分别为439、530和843K.     

Continuous compositional spread investigation of SiC-based thin films prepared by MW-ECR plasma enhanced magnetron co-sputtering

A kind of combinatorial material methodology,also known as continuous compositional spread method,was employed to investigate the relationship between the optical band gap and composition of SiC thin films.A wide range of SixCy thin films with different carbon contents have been successfully deposited in a single deposition by carefully arranging the sample position on the substrate holder.The films were characterized by surface profiler,x-ray photoelectron spectroscopy,ultraviolet-visible spectroscopy,fourier transform infrared spectroscopy and Raman spectroscopy.The carbon content y increases linearly from 0.28 to 0.72 while the sample position changed from 85 to 175 mm,the optical band gap changed between 1.27 and 1.99 eV,the maximum value corresponded to the stoichiometric SiC sample at the position of 130 mm,which has the highest Si?C bond density of 11.7×10^22 cm^-3.The C poor and C rich SixCy samples with y value less and larger than 0.5 were obtained while samples deviated from the position 130 mm,the optical band gap decreased with the Si?C bond density.     

全国核与辐射设施退役学术研讨会简介

在国家政府有关部门及中核集团公司支持下,由中国核学会辐射防护分会会同相关学会于2007年11月5日至10日在四川绵阳召开了全国核与辐射设施退役学术研讨会.     

球坐标系下中子输运方程泄漏项的简便推导

采用一种恰当的方法，简便地推导出中子输运方程泄漏项在球坐标系下的表达式，该方法避免直接寻求二面角与中子飞行距离之间的复杂微分关系，转而寻求二面角与其他平面角之间的几何关系，再利用其他平面角与中子飞行距离之间的微分关系（通常是已知的或比较容易推导得到），便可间接推导出中子输运方程泄漏项在球坐标系下的表达式。该方法与传统方法推导得到的表达式完全一致，且推导过程直观、物理图像清晰。      

Application of forward and adjoint Monte Carlo coupling technique to detector system designs

Forward and adjoint Monte Carlo coupling technique has been developed for analyzing neutron streaming in a system with large geometry. Particles (neutron and adjoint particle) are scored by surface type estimators such as the next event surface crossing estimators and the boundary crossing estimators. The detector response is calculated by folding the calculated neutron and adjoint angular fluxes. The reliability and efficiency for this method were studied by solving a sample problem of neutron streaming through narrow sodium pipe embedded in an iron shield. This method turned out to give a figure of merit several times better than the conventional method. The applicability of the method to detector system design has been demonstrated by calculating the signal to noise ratio for the fuel failure detector with delayed neutron detection method, which is located behind the reactor shield of concrete. This method gives an advantage in clarifying the spatial channels for neutron streaming.     

Spherical harmonics method for neutron transport equation based on unstructured-meshes

Based on a new second-order neutron transport equation, self-adjoint angular flux (SAAF) equation, the spherical harmonics (PN) method for neutron transport equation on unstructured-meshes is derived. The spherical harmonics function is used to expand the angular flux. A set of differential equations about the spatial variable, which are coupled with each other, can be obtained. They are solved iteratively by using the finite element method on unstructured-meshes. A two-dimension transport calculation program is coded according to the model. The numerical results of some benchmark problems demonstrate that this method can give high precision results and avoid the ray effect very well.     

非结构网格中子输运方程的球谐函数解法研究

从新的二阶自共扼角通量密度(SAAF：Self-Adjoint Angular Flux)中子输运方程出发．利用球谐函数对角度变量进行展开,导出了一组关于空间变量的偏微分方程组,中子通量密度的各个分量相互耦合,应用一定的迭代策略进行迭代求解。针对每一个方程,应用有限元方法对非结构网格进行离散求解。据此编写了二维球谐函数方法输运计算程序,对一系列基准题进行校算的数值结果表明,该方法具有较高的计算精度,克服了射线效应,并能用于非结构网格。     

Cellular neural network to the spherical harmonics approximation of neutron transport equation in x–y geometry. Part I: Modeling and verification for time-independent solution

This paper describes a novel method based on using cellular neural networks (CNN) coupled with spherical harmonics method (P_N) to solve the time-independent neutron transport equation in x–y geometry. To achieve this, an equivalent electrical circuit based on second-order form of neutron transport equation and relevant boundary conditions is obtained using CNN method. We use the CNN model to simulate spatial response of scalar flux distribution in the steady state condition for different order of spherical harmonics approximations. The accuracy, stability, and capabilities of CNN model are examined in 2D Cartesian geometry for fixed source and criticality problems.     

A least-squares finite-element Sn method for solving first-order neutron transport equation

A discrete ordinates finite-element method for solving the two-dimensional first-order neutron transport equation is derived using the least-squares variation. It avoids the singularity in void regions of the method derived from the second-order equation which contains the inversion of the cross-section. Different from using the standard Galerkin variation to the first-order equation, the least-squares variation results in a symmetric matrix, which can be solved easily and effectively. To eliminate the discontinuity of the angular flux on the vacuum boundary in the spherical harmonics method, the angle variable is discretized by the discrete ordinates method. A two-dimensional transport simulation code is developed and applied to some benchmark problems with unstructured geometry. The numerical results verified the validity of this method.     

Identification and properties of the fundamental expansion functions for neutron transport in an infinite homogeneous medium

Starting from the basic expression for the neutron flux due to a point source in an infinite homogeneous scattering and absorbing medium, the first few fundamental expansion functions corresponding to successive collisions are identified, and their analytic properties are presented, in spherical and plane geometry. Various representations of the functions are obtained in the form of power series, an expansion in a series of exponential integrals, and other integrals. The adequacy of traditional asymptotic forms is considered.     

Lattice Boltzmann method for simulation of time-dependent neutral particle transport

In this paper,a novel model is proposed to investigate the neutron transport in scattering and absorbing medium.This solution to the linear Boltzmann equation is expanded from the idea of lattice Boltzmann method (LBM) with the collision and streaming process.The theoretical derivation of lattice Boltzmann model for transient neutron transport problem is proposed for the first time.The fully implicit backward difference scheme is used to ensure the numerical stability,and relaxation time and equilibrium particle distribution function are obtained.To validate the new lattice Boltzmann model,the LBM formulation is tested for a homogenous media with different sources,and both transient and steady-state LBM results get a good agreement with the benchmark solutions.     

Lattice Boltzmann method for simulation of time-dependent neutral particle transport

In this paper,a novel model is proposed to investigate the neutron transport in scattering and absorbing medium.This solution to the linear Boltzmann equation is expanded from the idea of lattice Boltzmann method (LBM) with the collision and streaming process.The theoretical derivation of lattice Boltzmann model for transient neutron transport problem is proposed for the first time.The fully implicit backward difference scheme is used to ensure the numerical stability,and relaxation time and equilibrium particle distribution function are obtained.To validate the new lattice Boltzmann model,the LBM formulation is tested for a homogenous media with different sources,and both transient and steady-state LBM results get a good agreement with the benchmark solutions.