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.     

浅议μ介子断层扫描技术

μ介子断层扫描技术是一种新兴的探测成像技术,具备三维成像、零放射性污染、成本低、检测速度快、应用范围广等优点,尤其是在核材料探测领域的应用价值较高。阐述了μ介子断层扫描技术原理和优势,重点介绍了美国决策科学公司与洛斯.阿拉莫斯国家实验室研制的μ介子断层扫描系统。     

Aspects of Fokker-Planck transport

We apply to a simple example, taken from neutron thermalization, techniques we have been using in the study of Fokker-Planck transport of test particles. The example from neutron physics concerns the divergence of the series expressing diffusion length as a function of absorber concentration. In both cases, analytic continuation, and matched asymptotic expansion play a role.     

Display Processing of Computed Tomography Images

In this paper, we review some of the possibilities for digital enhancement of Computed Tomography (CT) images. The basic hypothesis is that the array of computed x-ray absorbtion values obtained in CT contains more information than the unaided eye can generally grasp. Examples of novel contrast enhancement and noise smoothing algorithms are included to support this hypothesis. Particular attention is paid to properties of the human visual system which we consider an element of the overall information processing loop.     

Progress toward Quantitative Computed Tomography

Progress in the quantitative use of CT numbers for patient diagnosis has been limited because of scanner drift, energy dependence, and various artifacts. The nature of these errors is discussed, and methods of evaluating them are described. In addition, remedial measures are mentioned, including the use of a three-point calibration phantom.     

用于正电子发射断层成像的闪烁晶体

正电子发射断层成像要求闪烁晶体材料具有高光输出、短衰减时间和强阻止本领,且价格低廉。本文综述了闪烁晶体材料最新的发展状况和其特征对正电子发射断层成像系统的性能影响。     

Social-Economic Aspects of Radiation Safety

Among the many scientific, technical, and social problems which nuclear power in the past century has encountered, the most significant are economy, safety, and public acceptability.The possibilities of increasing the economic efficiency by using boiling water vessel reactors with natural coolant circulation, the need to take account of not only the dose but radiation intensity when estimating biological effects of irradiation, and the problems of insurance for compensating radiation harm to the health of workers in nuclear cycle enterprises and the population are discussed. 2 figures, 17 references.     

Some Aspects of CAMAC Software

Since most CAMAC systems include computers, the generation and maintenance of computer programs may represent a substantial fraction of the effort involved in assembling a CAMAC system. The effort involved can be reduced if standard software can be used, but the generality of the hardware and the variety of computers and interfaces make the production of efficient, general software difficult. Some of the problems and some general approaches to them are discussed below. The NIM Software Working Group has been working on a set of FORTRAN subroutines for use with CAMAC systems. Though the effort is incomplete, it has reached a stage where its implementation is feasible and will prove useful. The working group has therefore concluded that it should be published in this tutorial issue to make it available to prospective users.     

Aspects of nuclear power economics

The article is a review of various aspects of nuclear power economics based on materials made available at the Second International Conference on the Peaceful Uses of Atomic Energy at Geneva, 1958.Currently, discussions are under way in various countries on the economic aspects of the use of atomic energy for the production of electric power, and the scheduling of the erection of atomic-fueled electric power plants. This article provides a rundown of the various major questions related to the structure of the initial capital outlay, an analysis of plant-operation factors, and their effects on the economics of atomic electric power plants.Problems of the economics of atomic electric power plants using fast reactors are dealt with in brief. Data are cited indicating that the prequisities exist for the economically justified use of the heat power of thermal reactors in power utility installations.In conclusion, it should be noted that a more extended experience in the operation of existing large-scale nuclear electric power generating power plants and the commissioning of new large-scale stations will make it possible to provide a definitive answer to questions arising in the economics of nuclear power engineering.     

对计算机断层扫描技术中几个问题的探讨

本文对计算机断层扫描技术中所选择滤波函数的不同，射线束宽度的差异，探测器的响应、数据的采样及旋转中心的偏移等因素影响图像重建质量分别进行了讨论和分析。实验结果表明，这几个因素对重建后的图像质量产生的影响都是不可忽视的，尤其是在某些情况下，将会导致产生较大的误差。     

Positron Ring Cameras for Emission-Computed Tomography

A properly designed circular ring of NaI(Tl) crystals and suitable reconstruction algorithms can provide rapid, high-resolution transverse section images of positron-labeled compounds in the human body. The spatial resolution is limited by the crystal center-to-center spacing and by the positron range in tissue. Using 280 crystals with 10-mm center-to-center spacing and isotopes such as 68Ga. 11C, 18F, or 52Fe, a resolution of 7.5 mm full width at half maximum (FWHM) is possible. Improvements in this technology will involve larger numbers of smaller crystals, more efficient crystals (possibly bismuth germanate), or faster detectors (such as loaded organic scintillators).     

Non-Hydrodynamic Aspects of Pool Boiling Burnout

More than 400 pieces of test sections—flat plates made of various metals and alloys—were placed in saturated water under atmospheric pressure and heated to physical destruction by passing electric current directly through them.

Several non-hydrodynamic parameters have marked effect upon the critical heat flux, which indicates that purely hydrodynamic theories are not directly applicable to general prediction of the critical heat flux.

The critical heat flux data was found to be well correlated with the heat capacity per unit surface area of the test section: the critical heat flux is reduced with decrease of this parameter, while with increasing parameter it approaches a certain asymptotic value.

The fluctuation of surface temperature due to alternate contact with vapor and liquid was calculated by the proposed model, and the trend of dryout duration was estimated from the critical heat flux data.     

Some Aspects of LWR's Water Chemistry

The hypothesis laid down in this paper offers an alternative to the current interpretation of the processes: hideout (hideout-return), crud deposition and change of the coolants activity level in the nuclear power reactors under different operating conditions.

This alternative is based on the supposition that the heat flux has not a direct effect on the processes mentioned above, but acts through the heat transfer mechanism in the boundary, caused by itself.

The boundary influenced by heat flow is in non-equilibrium state and in such system states (at adequate heat flux) non-equilibrium structures called dissipative structures arise which ale closely connected with heat transfer mechanism. The transport and the location of the colloidal corrosion products dispersed in steam generators-or reactor water during the units operation are strongly influenced by the existence of dissipative structures. The transport and location of the main part of ion species depend also on the existence of these structures because the colloidal particles act like collectors of the ions dissolved in the water (The ions are inserted in the colloidal particles double layer).

The hideout and hideout-return phenomena are interpreted as closely connected with the existence of the above mentioned dissipative structures. It was attempted to consider the changes in nuclide concentrations in the LWR coolant upon start-up and shutdown as hideout respectively hideout-return processes. The recent shutdown chemistry aspects are discussed also.