Robert C. Axtmann

Vibrational Relaxation and Electronic Quenching of the C 3Πu (υ′ = 1) State of Nitrogen

A molecular lifetime apparatus was used to study energy transfer processes of the C 3Πu state of nitrogen. Kinetic and luminosity measurements as a function of pressure indicate a cross section σ(3) = 2.5 ± 0.7 A2 for vibrational relaxation of N2(C 3Πu)υ′=1 by ground‐state nitrogen molecules. A useful result of the kinetic analysis is that although the observed lifetime (including quenching) decreases with υ′, vibrational relaxation reduces the gross C state luminescence decay to a single exponential, characteristic of the υ′ = 0 level. Natural radiative lifetimes and electronic quenching cross sections, σ(2), were determined for the υ′ = 0 and υ′ = 1 levels of the C state: υ′ = 0: τ = 40.5 ± 1.3 nsec and σ(2) = 1.98 ± 0.02 A2; υ′ = 1: τ = 44.4 ± 1.4 nsec and σ(2) = 1.42 ± 0.71 A2. Estimates of electronic and vibrational deactivation cross sections for the υ′ = 2 level are υ′ = 2: σ(2) = 3.9 ± 0.8 A2and σ(3) = 1.6 ± 0.4 A2. The efficiencies for excitation of the υ′ = 0 and υ′ = 1 levels by the secondary e...

Growth and ripening of silica polymers in aqueous solutions

Abstract The molecular weights and number densities of polymers formed in neutral solutions of silicicacid, at the low concentrations that are typical of hydrothermal waters, were determined by gel filtration chromatography. The polymers exhibit Ostwald ripening that is characteristic of growth limited by a first order reaction of monomer at the surfaces of growing particles. Three divalent inorganic salts at 0.1 M are more effective at promoting polymer growth than is sodium chloride at the same concentration. The results support a recent theoretical model of the silica polymerization reaction but also identify ways in which the model might be improved.

Tritium permeation through 304 stainless steel at ultra-low pressures

Abstract Many recent studies on the permeation of hydrogenic gases through metals suggest that deviation from classical behavior (permeation rate proportional to the half-power of the driving pressure) should occur at low pressures. In particular, Strehlow and Savage predict a transition region that is caused by competitive permeation through the metal itself and a defect-riddled coating. This work reports tritium permation measurements with a new apparatus that is capable of maintaining driving pressures as low as 10 −7 Pa — more than three orders of magnitude lower than those of previously reported experiments. The results with 304 stainless steel at 573 to 723 K confirm the Strehlow-Savage model and, in addition, indicate the existence of a thin but tough, residual film on the surface.

Nanosecond Fluorescence Apparatus with a Spontaneously Fissioning Excitation Source

We report the development of a versatile apparatus for the precise measurement of fluorescent lifetimes. Based on the pulse sampling method, the device utilizes a unique excitation source—a few microcuries of the spontaneously fissioning nuclide 252Cf. A stochastic analysis of distortion effects demonstrates that the random risetimes and amplitudes of the excitation pulses cause negligible distortion in comparison to that produced by convolution with the photomultiplier tubes impulse response function. Experimental results for the nitrogen second positive group (SPG) and the first negative group (FNG) were in excellent agreement with values reported by others. Simultaneous observation of the processes N2(C3Πu)→ lim k1N2(B3Πg)+hν,  and  N2(C3Πu)+N2(X1Σg+)→ lim k2products, gave τ=1/k1=40.5±1.3 nsec and k2/k1=1.75±0.06×10−2 Torr−1.

Excitation of Nitrogen Gas by Alpha Particles and Fission Fragments

Excitation of the SPG (second positive group: C 3πu→B 3πg) by fission fragments and by 6.1‐MeV alpha particles was studied with a pulse technique. Both types of particles exhibit nearly the same efficiency for excitation from which it was concluded that in either case secondary electrons are responsible for the production of the triplet states.

Emission control of gas effluents from geothermal power plants

Geothermal steam at the worlds five largest power plants contains from 0.15 to 30% noncondensable gases including CO(2), H(2)S, H(2), CH(4), N(2), H(3)BO(3), and NH(3). At four of the plants the gases are first separated from the steam and then discharged to the environment; at the fifth, the noncondensables exhaust directly to the atmosphere along with spent steam. Some CO(2) and sulfur emission rates rival those from fossil-fueled plants on a per megawatt-day basis. The ammonia and boron effluents can interfere with animal and plant life. The effects of sulfur (which emerges as H(2)S but may oxidize to SO(2)) on either ambient air quality or longterm human health are largely unknown. Most geothermal turbines are equipped with direct contact condensers which complicate emission control because they provide two or more pathways for the effluents to reach the environment. Use of direct contact condensers could permit efficient emission control if coupled to processes that produce saleable quantities of purified carbon dioxide and elemental sulfur.

Limitations on Tritium Transport Through Fusion Reactors

The propensity of gases and molten salts to impede tritium permeation have been examined, and the results indicate that helium as a coolant or flibe (LiBeF/sub 3/) as a blanket material would reduce tritium permeation in extant designs to negligible rates. For example, the tritium release rates from the Princeton Reference Design would be two to three orders of magnitude less than that calculated under the assumption (used in the design report) that fluids would not affect the permeation rate. The tritium permeation characteristics of novel reactor designs may be evaluated by a straightforward procedure. First, the tritium mass transport rates in the fluids are computed from the Chilton-Colburn j-factor analogies, the Gilliland correlations, or a simple transformation of heat transfer data. The asymptotic fluid-limited and metal-limited permeation rates are then equated to identify the tritium pressure regime in which a transition occurs in the rate-limiting mechanism.

Sulfur emission control for geothermal power plants

Abstract Hydrogen sulfide gas is present in hydrothermal waters that are useful for electric power production. Previous schemes for H2S emission control increase the costs of geothermal power. A modification of the classical Claus process for producing sulfur from H2S is compatible with many geothermal plant designs. In the presence of a market for sulfur, use of the process could decrease geothermal power costs.

Cost study of superheating geothermal steam

This study compares the electrical generating costs for hybrid plants, in which fossil fuel superheats geothermal steam, with those for conventional dual-flash plants. Parameters varied in the analysis include the resource temperature and the geothermal gradient. In order to make the results generally useful, we have made conservative estimates of site-dependent variables. The results indicate that superheating can significantly improve the economic competitiveness of geothermal resources that would normally be considered uneconomical. In addition, superheat will increase total plant outputs markedly and enhance thermal efficiencies by 30–40%.

Validity of experimental tests for chain reactions in batch reactors

Abstract Gas phase chain reactions are investigated for radiolytic and photochemical batch reactors. The steady state treatment leads to a nonlinear equation of continuity when there is competition between volume termination and wall termination of the chain carriers. The equation is solved analytically for several limiting cases and numerically for a range of experimental conditions. For many situations of experimental interest, and particularly ones that involve short chains, the numerical solutions indicate that the reaction yield may be remarkably insensitive to either pressure or dose rate. In such circumstances the existence of a chain reaction might easily be masked, as is demonstrated by an analysis of experiments on isotopic exchange in nitrogen gas.