Calculation of pixel detector capacitances through threedimensional numerical solution of the Laplace equation

A method for the solution of the three dimensional Laplace equation is presented. The method applies to planar geometry cases, such as pixel detector devices, characterized by mixed boundary conditions. Through this algorithm the capacitances associated with pixel detectors are calculated. These capacitances, which are the pixel to substrate and the interpixel capacitances, are of great importance in the design of a pixel detector since they influence the noise and the cross talk effects between pixels. Capacitances for various pixel and interpixel dimensions are presented along with an analytical approximation for the calculation of the total pixel capacitance     

Ambient Storage Effects and Mounting Problems of Very Large Volume Ge LID Detectors

Ambient Storage Effects and Mounting Problems of Very Large Volume Ge LID Detectors, Guy Armantrout - In order to better understand the problems involved in mounting and handling a large volume Ge LID detector, a study was undertaken of the surface-setting procedure before mounting and the effect of diode storage for varying periods of time at the ambient temperature. The diode surface potential, diode capacitance, and diode V-I characteristics were taken as a function of different surface treatments before mounting. The results were correlated using an inversion layer model for the diode. Leakage currents less than 0.5 nA at 3 kV have thus far been obtained. The compensated region of Ge LID diodes is slightly supersaturated with lithium at room temperature. These diodes tend to revert back to the original P-type material because of lithium precipitation. The rate of precipitation was found for several diodes and was found to be a function of the effective lithium mobility.     

Generalized Model Analysis of Ionizing Radiation Effects in Semiconductor Devices

The necessity of analyzing complex semiconductor device behavior in the radiation environment requires improved analytical methods for accurate representation. The purpose of this discussion is to present work done on the applicability of the Linvill lumped model in a generalized model analysis. The advantages of the lumped model technique include flexibility in detail of device representation (i.e., accuracy), an intimate coupling to the well known radiation effects in bulk semiconductor material, and a unified analytical technique for a wide range of devices. It is shown that the lumped model analysis provides an effective technique for analyzing simple as well as complex devices in a pulsed ionizing radiation environment. Included is the representation of a simple p-n junction diode, a grown-junction transistor; and a planar-diffused transistor with its monolithic-chip substrate and isolation junction. The lumped-model behavior of the diode and grown junction transistor is compared to previously available analytical results. Using measured parameter values, the quantitative lumped-model predictions are compared to experimentally observed transient radiation response. The transistor response is investigated as a function of quiescent emitter current and external base resistance. The effect of the substrate junction in the monolithic-chip transistor is qualitatively presented as a function of the transistor parameters and the substrate proximity.     

Thermionic Analysis by Use of a Digital Computer

As accurate and rapid techniques for analytical performance prediction of thermionic plasma diodes are presently lacking, an IBM digital computer program has been developed to semiempirically predict diode performance. Experimental curves of voltage versus current are presented for tantalum, molybdenum, and rhenium for a wide range of emitter and cesium temperatures. These are processed by the program to determine the optimum efficiency characteristics for various emitter temperatures. Graphical presentations of the processed data indicate the maximum obtainable efficiencies using any of the three emitter materials. The corresponding values of cesium temperature and diode voltage necessary to obtain this efficiency and the corresponding power densities are also presented.     

Thermionic Analysis by Use of a Digital Computer

As accurate and rapid techniques for analytical performance prediction of thermionic plasma diodes are presently lacking, an IBM digital computer program has been developed to semi-empirically predict diode performance. Experimental curves of voltage versus current are presented for tantalum, molybdenum, and rhenium for a wide range of emitter and cesium temperatures. These are processed by the program to determine the optimum efficiency characteristics for various emitter temperatures. Graphical presentations of the processed data indicate the maximum obtainable efficiencies using any of the three emitter materials. The corresponding values of cesium temperature and diode voltage necessary to obtain this efficiency and the corresponding power densities are also presented.     

Efficient modeling of Compton diode gamma radiation detectors

The CEPXS/ONELD code package proved to be significantly more efficient than electron Monte Carlo for computing spherical Compton diode response to gamma irradiation. The authors review the mechanism responsible for the production of electric currents in Compton diodes, describe the calculation method, and present results for a few representative Compton diodes. The adjoint capability of CEPXS/ONELD allows the complete energy-angle response of a Compton diode to be determined with a single transport calculation. The calculated results compare well with measurement for energies between 0.5 MeV and 4.4 MeV. Because the calculations are so fast, many potential Compton diode designs with different dimensions and materials can be modeled, and the best design chosen for production     

Gamma Dosimetry by the Microplasma Phenomenon

The feasibility of employing commercially available, microwave P-N avalanche diodes as gamma radiation dosimeters was investigated. The detection method used to determine the magnitude of the radiation dose consisted of measuring the microplasma pulse counte-rate before and after the irradiation. The feasibility of this approach was established. The technique that was determined as suitable fcr this purpose consists of recording the peak on the pulse count-rate versus diode noise voltage curve. This count-rate peak was found to vary linearly with the gamma radiation dose between two dose limits, both of which are determined from the physical characteristics of the diode used. Three types of microwave diodes were used, and criteria were developed for selecting the most efficient microwave diode size for the radiation dose range of interest. In the course of the investigation it was also shown that the defect center introduction rate was dependent upon the physical size of the dosimeter for devices in the size range of the avalanche diodes used in this study. The specific diodes used had a Junction area range of from 0.6×10-4 to 7×10-4 cm2. By introducing the diode size as a variable in the damage data equation it was possible to obtain a reasonable correlation with silicon radiation damage data from the period 1963 to 1967. The size of the microplasma in the avalanche region was estimated from the data of this investigation and the estimate was found to correlate well with experimental data from the mid-1960' s.     

Simplified Engineering Techniques for Predicting Diode Tree Responses

The feasibility of predicting equilibrium photocurrents in silicon switching diodes entirely from nondestructively measured electrical parameters is shown. The prediction method is derived from the basic theoretical equation for diode photocurrent. Junction areas and depletion widths are related to avalanche voltages and capacitance-voltage characteristics by a general solution to McKay's avalanche condition integral equation. Diffusion lengths are related to storage times. The feasibility of the prediction method is demonstrated by comparing predicted and measured values of equilibrium photocurrents in 46 test diodes.     

四路并联二极管辐射X射线场参数计算

利用二极管的电压、电流计算了发射电子束能谱参数,建立了四路并联二极管阳极靶蒙特卡罗粒子输运计算模型,给出了辐射X射线场参数;将四路并联二极管的每个二极管划分为若干小单元,将其作为点源,采用数值积分的方法计算了辐射X射线剂量分布,并分析了空间不同位置处每路二极管对剂量的贡献。结果表明:真空中,距离四路并联二极管阳极靶5cm位置处,X射线注量为3.55mJ/cm2,光子平均能量为62.18keV,120keV以下的光子占辐射X射线谱总能量的81.84%,电子束转换效率为0.30%;在2 700cm2范围内,中轴线和对角线上的剂量均匀性分别为3.20和6.31;在2 000cm2范围内,中轴线和对角线上的剂量均匀性均小于2。     

Optimum Design of Sensitive Tunnel Diode Discriminators

A new and useful theory was developed to characterize switching properties of the tunnel diode. Expressions for time delay and time variance for small signals in the presence of amplitude noise were developed for the tunnel diode in the discriminator mode. The expression for time variance is used to determine the parameters of the tunnel diode, and the tunnel diode bias condition to obtain the optimum time resolution for a specified signal and noise. The minimum charge necessary to switch the tunnel diode is calculated for a given signal current pulse width and tunnel diode bias condition. The expressions characterizing the properties of the tunnel diode were developed after the author discovered experimentally that the positive resistance region of the device could be represented very accurately by a sine function in voltage. Since this region of the characteristic curve is responsible for the significant delay and time variance, it is sufficient to describe these properties of the tunnel diode discriminator. The usual equivalent circuit is used to represent the tunnel diode. The second order nonlinear differential equation which is necessary to describe the equivalent circuit is simplified by excluding terms which were insignificant for this particular mode of operation. The simplified differential equation is solved to determine the time for the tunnel diode to switch from its stable bias point to the negative resistance region. This switching time, or delay time, is then used to calculate the time variance.     

Neutron radiation effects in GaAs planar doped barrier diodes

The degradation of GaAs planar doped barrier diodes subject to neutron irradiation is discussed. It is shown that for fluences as high as 10¹⁵ cm^-2, the diode characteristics are very well preserved, which strengthens the rationale for using these devices in place of Schottky diodes in harsh working environments such as nuclear instrumentation and space     

Tunnel Diode Analog to Digital Converter

A 10 channel tunnel diode analog-to-digital converter (ADC) has been constructed and tested. The converter is a simple stacked discriminator with tunnel diodes used as the quantization elements. The device has a conversion time of less than 10 nanoseconds and a differential linearity on the order of ± 3%.     

Application of the Wiener-Hermite functional method to point reactor kinetics driven by random reactivity fluctuations

The Wiener-Hermite Functional (WHF) method has been applied to the point reactor kinetic equation excited by Gaussian random reactivity noise under stationary conditions. Delayed neutrons and any feedback effects are disregarded. The neutron steady-state value and the power spectral density (PSD) of the neutron flux have been calculated in a second-order (WHF-2) approximation. Two cases are considered: in the first case, the noise source is assumed to be white, while in the second case the source is low-pass white noise. In both cases the WHF-2 approximation of the neutron PSDs leads to relatively simple analytical expressions. The accuracy of the approach is determined by comparison with exact solutions of the problem. The investigations show that the WHF method is a powerful approximative tool for studying the nonlinear effects in the stochastic differential equation.     

Large eddy simulation of unsteady flow in vortex diode

Vortex diode, as an important component in power fluidics, has been widely used in nuclear reprocessing engineering for about two decades. The fluidic system with vortex diodes is always working under a condition with a pulsant pneumatic power input. However, no detailed analysis of the unsteady flow inside the vortex diodes is available. Therefore, we carried out large eddy simulation (LES) to investigate the transient start-up process on the foundation of the experiment by Jacob et al. The numerical results were compared with the experimental data. It is shown that the special flow-time profiles in the start-up process are well predicted. From a further analysis on the internal flow, it is indicated that the change of flow rate with time is relevant to the varying of internal flow pattern and the swirling level. The above-mentioned methods and results of the vortex diode are of great guiding significance to predict the transient performance of the fluidic transfer system.     

A MCM-D-type module for the ATLAS pixel detector

For the ATLAS experiment at the planned Large Hadron Collider (LHC) at CERN hybrid pixel detectors are being built as innermost layers of the inner tracking detector system. Modules are the basic building blocks of the ATLAS pixel detector. A module consists of a sensor tile with an active area of 16.4 mm×60.4 mm, 16 read out ICs, each serving 24×160 pixel unit cells, a module controller chip, an optical transceiver and the local signal interconnection and power distribution busses. The dies are attached by flip-chip assembly to the sensor diodes and the local busses. In the following a module based on MCM-D technology will be discussed and prototype results will be presented     

InGaAsP多量子阱激光二极管及其组件的γ辐射效应

本工作进行多量子阱激光二极管及其组件的γ辐照实验研究,总剂量（以Si计）达5.5×10⁴Gy。结果表明：多量子阱激光二极管抗γ射线辐照能力很强,在实验总剂量下,裸管形式的多量子阱激光二极管的P-I特性、I-V特性及中心波长基本未变化。而多量子阱激光二极管组件因包含光学窗口、耦合透镜及光纤等附属光学元件,这些附属元件受γ辐照后光学性能下降,最终导致激光二极管组件输出光功率随总剂量增大而下降,停止辐照后,不需加偏置,在室温下即能发生退火,使得斜率效率逐渐回升。     

Large-Volume Coaxial Germanium Gamma-Ray Spectrometers

Germanium lithium-drift p-i-n diodes for high resolution 7-ray spectroscopy have been made with sensitive volumes in the range 16 to 54 cm3 (1 to 3.3 in. 3) using the coaxial method of drift. Details of the construction, mounting and preparation as spectrometers are given. The shape of the undrifted p-type core has been determined by scanning with a collimated 7-ray beam and by copper plating the surface of a sectioned diode. The characteristics as spectrometers, using 7-rays of energies in the range 0.1 to 7.5 MeV, are shown. At 122 keV energy, resolutions of 5.0 and 4.4 keV (fwhm) were obtained with diodes of sensitive volumes 23 and 54 cm3 respectively. A 16 cm3 volume diode had a resolution of 4.8 keV at 1533 keV 7-ray energy, and a 45 cm3 diode had resolutions of 6.5 and 19 keV at energies of 1.1 and 5.1 MeV respectively. The diodes were operated at bias voltages in the range 600 to 1500 V. Intrinsic full energy peak efficiencies are shown for different diode sizes over a range of 7-ray energies. For the 54 cm3 volume diode, these efficiencies are 21% and 8% respectively for 7-ray energies of 0.5 and 1.0 MeV with a source to diode distance of 30 cm. The larger diodes show a greatly enhanced peak/total ratio, and the higher efficiencies make these spectrometers extremely useful in reaction y-ray, y-7 coincidence, and n, y studies.     

Kinetic equation approach in surface transmission for axial channeling

Thermal fluctuations in surface transmission for axial channeling have been treated with a diffusion equation based on the kinetic equation in phase space. The steady increase model applied earlier is derived as an approximation to this treatment and it is shown to be particularly well suited for this problem. Single scattering has been included by a simple analytical model. Numerical results for the contribution to the Barrett factor on the minimum yield are compared with results of computer simulation.     

ABSTRACTS OF JAPANESE ARTICLES

A new approximate method for calculating the effectiveness of multiple control rods fully inserted in a reactor is described. This method is appicable to a bundle of many control rods, regardless of the number of rods, as well as to an array of a limited number of few rods.

Using either the sink model or the well model, a reactor equation of kernel form is obtained. The reactor equation is a two-dimensional diffusion equation with two-group diffusion kernel. In order to facilitate numerical computation of the eigenvalue, the integral equation is reduced to a set of linear homogeneous equations, by dividing the reactor into a large number of unit cells containing at most one control rod.

This method has been programmed for the IBM 7090, the code being given the designation ELC. The iterative procedure used converges much faster than the standard accelerated finite-difference programs. Using the ELC code, the effectiveness of an array of four control rods fully inserted in a cylindrical reactor was calculated. The results are in good agreement with those found by the Scaletter-Nordheim method. In the case of a large number of control rods, there is no alternative method to be compared with.     

The effect of the electron irradiation on the series resistance of Au/Ni/6H-SiC and Au/Ni/4H-SiC Schottky contacts

The effect of electron irradiation on Au/Ni/6H-SiC and Au/Ni/4H-SiC Schottky contacts has been studied by current voltage (I-V) characterization at room temperature. The diodes have been subjected to the electron irradiation at various energies (6, 12 and 15 MeV) and influence of the electron irradiation on the diode parameters such as barrier height, ideality factor, and series resistance has been studied. Cheung functions, Norde model and conductance method have been used to determine the diode parameters. The ideality factor of the diodes is greater than unity indicating activation of some other current transport mechanism(s). The series resistances of the diodes increase by increasing electron energy. The reverse current increases for the Au/Ni/6H-SiC diode after each electron irradiation experiment, while decreasing trend is observed for Au/Ni/4H-SiC diode. Decrease in the barrier height of Au/Ni/4H-SiC diode is observed and mainly attributed to the increase of the reverse current, while the decrease of the forward current is caused by increase in series resistance, for high electron irradiation energies.