Richard T. Schneider

Fissioning uranium plasmas and nuclear-pumped lasers

Current research into uranium plasmas, gaseous-core (cavity) reactors, and nuclear-pumped lasers is discussed. Basic properties of fissioning uranium plasmas are summarized together with potential space and terrestrial applications of gaseous-core reactors and nuclear-pumped lasers. Conditions for criticality of a uranium plasma are outlined, and it is shown that the nonequilibrium state and the optical thinness of a fissioning plasma can be exploited for the direct conversion of fission fragment energy into coherent light (i.e., for nuclear-pumped lasers). Successful demonstrations of nuclear-pumped lasers are described together with gaseous-fuel reactor experiments using uranium hexafluoride.

Reply to ’’Comments on nuclear‐pumped cw lasing of the 3He‐Ne system’’

In a recent comment by Prelas and Schlapper, the statement was made that in a paper by Carter, Rowe, and Schneider, the Ne line at 632.8 nm claimed to be observed could not have been observed, since the upper state population of the laser transition could not have possibly have been sufficient to allow lasing. The comment is based on a simple model introduced by Prelas and Schlapper. We show, in this response, that this model is conceptually wrong. In addition, a calculational error was made when they computed the power input to be 4.7 mW/cm3 rather than the correct value of 9.8 mW/cm3.

Computerized Spectrum Analysis

A system to automatically reduce and analyze the data on a spectrogram is in current use. The techniques used and the system are described. The systems principal components consist of a scanning densitometer with a built-on linear encoder, a 16-kc word rate analog-to-digital converter, and an IBM 1800 process computer with magnetic disk memory. The photomultiplier signal, which is proportional to the relative transmissivity of the spectrogram, is sampled at intervals of 2 or 4 μ. For a typical dispersion, this corresponds to approximately 0.025 Å. The sampled data are permanently stored on the disk memory. Typical processing time to scan one 12-cm spectrogram is 3 to 5 min. The stored data are further processed to locate all significant lines, to assign wavelengths to each line, and to determine relative intensities of the lines. The spectrum is plotted for visual interpretation and further analysis.

Measurement of the Temperature and Partial Pressure of a Uranium Plasma

The generation of a high-pressure uranium plasma is described. Determinations of temperature, uranium-II, and electron pressure are performed. The Boltzmann plot technique and the single-line, relative-intensity method are used. Radial distributions of the measured quantities across the plasma are given. Plasma temperature as a function of power input and pressure is measured. These temperatures range between 7900 and 10 300 K. Uranium partial pressures between 0.1 and 1.0 atm are deduced.

Mechanical Model Of The Insect Eye

Most optical instruments in use are modeled after the human eye. The design of insect eyes is fundamentally different and is governed by the laws of multiaperture optics. It can be shown that for certain applications, instruments using multiaperture optics are superior to single aperture instruments. For study of multiaperture optics and function of the insect eye a mechanical model resembling an insect eye was constructed. An individual eyelet of the mechanical model consists of a lens system and a detection system. The diameter of the front lens is 2mm (7mm fl), the aperture of the back lens is lmm (2mm fl). Each eyelet has seven optical fibers which transport the incident light to individual detectors. The model has a total of 100 eyelets (700 detectors). Each detector is sequentially read by a multiplexer which is interfaced with a micro computer, which displays the output on a video terminal.

Gaseous Fuel Reactor Research

Gaseous Fuel Nuclear Reactors are externally moderated and contain the fissile material inside a cavity where it is suspended by fluid mechanics forces. The gaseous phase of the nuclear fuel permits operation of the reactor at temperatures much higher than the melting point of all materials. NASA has originally supported relevant research for space propulsion. The continuation of this work includes now research on power generation on Earth for improved economy and environmental acceptability. In reactor experiments with enriched uranium hexafluoride, UF6, a critical mass of 6 kg is determined. Pressurized UF6 remains chemically stable at temperatures up to 2000 kelvins. The interaction of fission fragments with their gaseous environment causes preferential excitation and ionization, leading to non-equilibrium optical radiation. Powerful fluxes of photons are expected to become a superior mechanism of energy extraction from the fissioning gas or plasma in the reactor. The pumping of lasers solely by fission fragments is realized in a variety of lasants. A near term objective of the NASA gaseous fuel reactor program is a benchmark experiment at 100 kw power and at a gas temperature of 1600 kelvins, demonstrating the feasibility of major advances in reactor technology. A concerted research effort is leading to this experiment. A plasma core cavity reactor for high specific impulse propulsion in space reminas a long range goal.

Nuclear Pumped Lasers Utilizing Radiant Transfer

A nuclear pumped laser is a laser where the excitation is accomplished by nuclear energy. There are, of course, many nuclear reactions where nuclear energy is released (e.g., the He(n,p)T reaction), however, the concept tacitly assumes that the reaction is selfsustaining. Therefore the ultimate goal has to be to find a concept which uses fission energy for laser excitation. This could be the kinetic energy of the fission fragments, in the case of fission fragment pumping, or the fission energy has to be converted into some other form of energy which is then used to excite the laser medium. To use x-rays or the neutron radiation extracted from the core would be inefficient since the majority of the fission energy is invested in the kinetic energy of the fission fragments.

Wavelengths of U III and U IV lines in the near ultraviolet

Recent interest in isotope separation schemes which involve plasmas requires information concerning the wavelengths of highly ionized uranium lines, especially U III and U IV. The study reported here was undertaken to contribute to this required knowledge and was limited to the near UV. (AIP)

Measurement of Electrode Erosion during High-Voltage Vacuum Breakdown

This paper is concerned with the measurement of the mass of electrode material released by the electrodes during a high-vacuum breakdown. The techniques used in the experiment described in this paper for quantitative measurement of material released from the electrodes are neutron activation analysis and gamma-ray spectrometry. The method permits determination of the small masses released during the discharge. The threshold energy density required for material release is 15 J/mm2. An empirical equation is given for the material erosion for copper and a curve is given that relates mass erosion versus stored energy for copper electrodes. The experiment indicates that the mechanism responsible for current transport between the electrodes in a vacuum breakdown is a highly ionized plasma formed from the released electrode material.

Simplified Pattern Recognition Based On Multiaperture Optics

Multiaperture optics systems are similar in design to the concepts applying to the insect eye. Digitizing at the detector level is inherent in these systems. The fact that each eyelet forms one pixel of the overall image lends itself to optical preprocessing. There-fore a simplified pattern recognition scheme can be used in connection with multiaperture optics systems. The pattern recognition system used is based on the conjecture that all shapes encountered can be dissected into a set of rectangles. This is accomplished by creating a binary image and comparing each row of numbers starting at the top of the frame with the next row below. A set of rules is established which decides if the binary ones of the next row are to be incorporated in the present rectangle or start a new rectangle. The number and aspect ratios of the rectangles formed constitute a recognition code. These codes are kept and updated in a library. Since the same shape may give rise to different recognition codes depending on the attitude of the shape in respect to the detector grid, all shapes are rotated and normalized prior to dissecting. The rule is that the pattern is turned to maximize the number of straight edges which line up with the detector grid. The mathematical mechanism for rotation of the shape is described. Assuming a-priori knowledge of the size of the object exists, the normalization procedure can be used for distance determination. The description of the hardware for acquisition of the image is provided.