基于单片机的宽量程X-γ剂量率连续监测仪

本文介绍了一种基于单片机技术的宽量程X-γ剂量率连续监测仪的电子线路的设计思想,并描述了该电子线路部分的软、硬件设计方法,并着重介绍了软、硬件设计中若干难点的解决方法.     

束流位置探头用于束团电荷量测量的数值仿真研究

加速器常用的束流位置探头为电磁耦合型,其输出信号包括束流位置信息和束团电荷量信息.本文采用数值仿真方法研究探头电极和信号与束流位置之间的关系,基于Matlab开发一个用于仿真计算探头电荷量标定系数的软件包.对上海光源储存环束流位置探头的仿真结果表明,探头流强标定系数在2.5 mm半径内差值小于千分之二,在此精度范围内可认为流强标定系数为常数.     

基于CdZnTe探测器的核素探针探头的研制

为了解决在核医学手术中使用放射性核素进行病灶定位的难题,设计了一种基于碲锌镉(CdZnTe)探测器的核素探针探头。该核素探针探头主要包含CdZnTe探测器、低噪声电荷灵敏前置放大器和快驱动电路。考虑到环境本底和外界电磁干扰,对探针探头的结构作了特殊设计,该特殊设计能够提高核素探针探头的探测能力。探头中的放大器和快驱动电路能明显的放大核脉冲信号的幅度和提高核脉冲信号的信噪比,便于后端信号处理分析系统对信号的进一步处理。     

用于γ辐射场测量的差分电离室的设计

设计了一种用于测量γ辐射场的高气压差分电离室。采用双电离室、单输出的探头结构和添加铅屏蔽体相结合的方法,实现了强γ辐射场中特定方位γ辐射信号的差分测量技术。通过蒙特卡罗模拟和试验测试,在探头外包裹锡带的探测器获得了较好的能量响应线性。同时,还介绍了与差分电离室相配套的弱信号放大电路的设计。     

低场脉冲核磁共振仪探头的研制

探头是低场脉冲核磁共振仪中最灵敏的重要部件.与其他类型的探头相比,采用螺线管线圈的探头能获得高Q(品质因素)值与良好的磁场均匀性.本文通过对螺线管探头电路的分析,推导出了设计制作此类探头的理论公式,并以此设计制作了高品质的探头,同时对于设计中高性能元器件的选型以及探头的调试方法给出了详细的说明.     

核磁共振癌症诊断数据处理技术的研究与实现

分析了癌症临床诊断领域中MRI、MRS、PACS和小波变换技术的应用研究现状,针对目前主流核磁共振设备的特点,利用医疗图像存档与通信系统(PACS),提出了基于FTP/Telnet网络通讯技术从不同核磁共振设备获取NMR数据的方法.研究了FID信号的存储格式,以Philips Intera1.5T系统产生的FID信号向Windows标准格式的转换为例,给出了适用于目前主流核磁共振设备的核磁共振底层数据格式转换的方法,并给出了具体的程序实现.基于小波变换阈值去噪技术进行了FID信号的去噪研究,利用自行构造的小波滤波器组取得了较好的去噪实验效果.     

示波器探头种类及其工作原理

介绍了示波器探头的种类及其工作原理,主要从探头的负载效应、探头的补偿、探头的接地引线电感等方面论述了示波器探头在测量过程中对被测信号的影响和注意的一些问题.     

基于小波变换的低场脉冲核磁共振信号滤波

低场脉冲核磁共振信号在去除噪声的同时不能损失峰值与边沿有用信息.本文首先介绍了基于平稳小被变换的空域阚值滤波法,然后提出对小波系数先平移以保证边沿对齐再做相邻尺度乘积的改进,并给出新的空域相关阈值计算公式,试验表明该方法在有效保护核磁共振信号峰值与边沿的同时很好地抑制了噪声.     

230MeV超导回旋加速器磁场测量装置

<正>磁场等时性和聚焦性是衡量230 MeV超导回旋加速器性能优劣的关键指标之一,其判断标准必须通过测量加速器中心平面磁场来确定。为得到准确可靠的磁场测量数据,本文设计了一套能同时搭载霍尔探头和感应线圈两种测量方式的磁场测量装置。该套磁场测量装置包括核磁共振探头驱动机构、角向驱动及定位机构、径向驱动及定位机构、搭载霍尔探头和感应线圈的滑动机构、测量臂和     

BEPCⅡ亮度监测系统前端电子学

针对北京正负电子对撞机第二期(BEPCⅡ)基于每个束团亮度监测的快速亮度监测系统对探测器前端电子学的性能要求,设计和实现了包括大动态输入范围的高速前放、程控高速信号甄别、双探头信号反符合,以及信号整形和传输在内的前端电子学系统.测试结果显示前端电子学能够满足4 ns间隔的bunch-by-bunch的快速亮度监测系统的应用要求.     

Interaction between point defects in the Si–SiO2 system during the process of its formation

The results of the studies of the point defect generation kinetics in the Si–SiO₂ system by means of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) are presented. It has been established that the EPR and NMR signal intensities change non-monotonously with oxide film thickness and the maximum of the EPR and minimum of the NMR signals occur at the same oxidation time. This can be connected with the competition between the generation and transformation of the point defects, the formation of Si–O bonds and strained bonds rupture in the Si–SiO₂ system during the process of its formation. The defect structure of the Si–SiO₂ system depends on the point defects density in initial wafers. A possible mechanism to explain this interdependence has been discussed.     

Study of R.f., Gradient Pulse and Magnet Instability Effect in NMR Tomography

Newly emerged NMR imaging requires careful studies on r. f. pulse shapes and sequencing for the selection of the region, gradient pulsing for the 2- or 3-D spatial coding, and suitable signal handling technique for the compensation of the inherent instability of the system, especially fluctuation of the static magnetic field. Above subjects are discussed in detail and a new method which would be useful for the line integral projection reconstruction is proposed. The method could equally be applied to other 3-D NMR imaging techniques such as KWE (Kumar-Welti-Ernst) direct Fourier reconstruction or planar integral projection type reconstruction.     

Behaviors of Electron Heat Transportation in HT-7 Sawtoothing Plasma

It is found that in HT-7 ohmic plasma, main energy loss comes from electron heat conduction, hence quantitative data of electron heat diffusivity is a very important issue for investigation of electron heat transportation behavior in different target plasmas so as to get high performance plasma. A time-to-peak method of the heat pulse propagation originating from the sawtooth activity on the soft x-ray intensity signal has been adopted to experimentally determine electron heat diffusivity χe^HP on the HT-7 tokamak. Aiming to improve the signal-to-noise (S/N) ratio of the original signal to get a stable and reasonable electron heat diffusivity χe^HD value, some data processing methods, including average of tens of sawteeth, is discussed. The electron heat diffusivity χe^HP is larger than χe^PB which is determined from the balance of background plasma power. Based on variation of the measured electron heat diffusivity χe^HP , performances of different high confinement plasmas are analyzed.     

应用小波分析估计核磁共振测井信噪比

核磁共振的信噪比在T2谱反演中起着重要作用,但是常规的估计方法依赖于奇异值的截断值选取以及控制方程组的系数矩阵,因而给噪声方差的估计带来一定的任意性,并且不能自适应于信号的变化。提出了一种小波估计方法,该方法估计的噪声方差仅仅与信号有关,与控制方程组无关,并且能够自适应于信号的变化,由其给出的噪声信号具有高斯分布特性。     

Limited Angular View Planar-Integral Projection Reconstruction in NMR Imaging

Limited angular view planar-integral projection reconstruction for fast multislice imaging in NMR is proposed and its efficacy is studied. Alghough it is known that the planar-integral projection reconstruction (PPR) method has advantages in signal to noise ratio improvement in NMR imaging, necessary data acquisition time is too long to be of practical value. In this paper, a study is undertaken on the variations of the PPR method which would lead to a shorter data acquisition time than the orginal PPR method. Also a new method which provides high quality multislice images through the use of limited angular view data acquisition mode is introduced. Computer simulation results and experimentally obtained images are presented for the demonstration of the potential of the method for clinical applications.     

Analysis of Enhanced Laser-Induced Breakdown Spectroscopy with Double Femtosecond Laser Pulses

In this paper,an experimental study of collinear geometry double-pulse femtosecond LIBS was performed on a Ni sample in ambient air in an effort to clarify the contributing processes responsible for the signal enhancement observed in comparison with the single-pulse case.Doublepulse LIBS spectra show a very clear enhancement when an optimum inter-pulse delay was used.The influences of the inter-pulse delay between two pulses on the LIBS signal intensity,electron temperature and density were investigated.It is most remarkable that the evolutions of signal enhancement and electron temperature versus the inter-pulse delay showed the same behavior and revealed two main regimes of interaction.These results provide additional insight into the possible emission enhancement mechanisms in the double pulse configuration.     

EPICS interface to Libera electron beam position monitor

SSRF diagnostics system will adopt a new generation digital electron beam position processor,Libera,as the signal condition,signal processing and data acquisition device for beam position monitor.In order to provide a uniform data and control interface for users,we developed an EPICS interface based on Control System Programming Interface(CSPI)layer,allowing the performance of the electron beam to be monitored through EPICS channels.In this interface a new record type for BPM was defined and its associated support routines were implemented.     

Analysis and Characterization of Pre-Diffusion in Multi-Linear Silicon Drift Detectors

Multi-linear silicon drift detectors (MLSDD) are silicon detectors in which signal electrons are confined within parallel drifting columns at few micrometers from the anodes' surface and transported towards point-like anodes by an electrostatic field. During the initial motion across the thickness the signal electrons spread in all directions to a given width - we call this phenomenon pre-diffusion - until the signal electrons are focused in the drift channels which suppress any further spread into adjacent channels. This work is devoted to the study of the initial motion of the electron cloud when the electrons are being focused toward the minimum of the potential energy. We developed an analytical model to predict the initial charge spread and carried out a detailed measurement campaign to evaluate the impact of the detector operating conditions and of the charge injection level on the initial charge spread. The design of the electron spread during pre-diffusion allows optimization of MLSDD for different applications.     

量程至MGy的石英剂量计性能研究

为建立剂量可至MGy超高剂量范围的新型剂量计,本研究以石英为敏感材料,利用电子自旋共振（ESR）方法测量样品经γ射线或电子束辐照后产生的信号强度,开展石英种类选择、辐照后的线性、稳定性研究。结果表明,高纯石英适合作为超高剂量范畴的工作剂量计原材料。石英样品辐照后经15 min、300 ℃的热处理,信号强度在一年内能保持较好的稳定性,变化<3% ,且其吸收剂量与石英E′信号强度在10~10³ kGy剂量范围内成一定的函数关系,两者之间的拟合系数>0.99,相比于未经热处理的高纯石英样品,稳定性及拟合函数R²均得到明显提升。以上结果表明,石英剂量计适合作为超高剂量范畴的工作剂量计。     

Research on the Real-Time Phase Jump Process Method for Plasma Electron Density Measurement in HL-2A Tokamak

In the real-time plasma electron density measurement using far infrared(FIR) laser interferometry, the plasma electron density can be calculated by measuring the real time phase difference between the reference signal and the probe signal. A novel Real-time Phase Jump Process(RPJP) method is applied to the HL-2A tokamak. With this method, the phase difference precision is up to1/3600fringe(1 fringe is equal to a phase shift of 2π), and the dynamic measurement range is extensible 65536 fringes. The time resolution of the phase difference is 80 ns, while the feedback delay is 180 μs.