Showing papers by "Oak Ridge National Laboratory published in 1977"

Electron excitation and the optical potential in electron microscopy

Abstract: A theory for inelastic scattering of fast electrons in solids is developed, based on an extension of the theory of scattering in an electron gas. Values of the inverse mean free path and related optical potential can be computed quite conveniently. It appears that, particularly in the case of solids characterized by high atomic numbers, the contribution of inelastic scattering to the optical potential for fast electrons may have been considerably over-estimated by electron microscopists in the past.

The Effects of Antioxidants on Skin Tumor Initiation and Aryl Hydrocarbon Hydroxylase

Abstract: Summary Butylated hydroxytoluene, butylated hydroxyanisole, and vitamins C and E are effective inhibitors of 7,12-dimethylbenz( a )anthracene tumor initiation in a two-stage system of tumorigenesis. These antioxidants did not significantly induce epidermal aryl hydrocarbon [benzo( a )pyrene]hydroxylase, nor did they have any effect when added directly to the in vitro aryl hydrocarbon [benzo( a )pyrene]hydroxylase assay. However, butylated hydroxytoluene and butylated hydroxyanisole, when applied topically to mice, inhibited the in vitro , epidermally mediated, covalent binding of radioactive benzo( a )pyrene and 7,12-dimethylbenz( a )anthracene to DNA. When butylated hydroxytoluene and butylated hydroxyanisole were added in vitro , they did not inhibit the epidermally mediated covalent binding of the hydrocarbons to DNA. The inhibition of polycyclic hydrocarbon tumorigenesis by antioxidants may be related to the ability of antioxidants to prevent the in vivo activation of hydrocarbons to carcinogenic epoxides and/or other electrophilic intermediates or may be related to their ability to increase detoxification of the reactive intermediate that requires intact cells to be operational. In any event, the results suggest that the antioxidants have an indirect effect on the epidermal metabolizing system which leads to a decrease in covalent binding to DNA.

Measurement of the thermal-expansion coefficient of nickel from 300 to 1000 K and determination of the power-law constants near the Curie temperature

Abstract: A fused-quartz dilatometer was used to measure the thermal-expansion coefficient $\ensuremath{\alpha}$ of nickel between 300 and 1000 K. Measurements on National Bureau of Standards certified copper and tungsten standards with the dilatometer established the uncertainty in the $\ensuremath{\alpha}$ measurements on nickel as \ifmmode\pm\else\textpm\fi{} 0.8% (\ifmmode\pm\else\textpm\fi{}0.10 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ ${\mathrm{K}}^{\ensuremath{-}1}$), except within \ifmmode\pm\else\textpm\fi{} 2 K of the Curie temperature ${T}_{C}$ where the uncertainty was about \ifmmode\pm\else\textpm\fi{} 1.6%. Results of 38 investigations of the expansion of nickel reported in the literature were analyzed critically, resulting in a compilation of $\ensuremath{\alpha}$ of nickel from 0 to 1500 K. Theories of thermal expansion were employed to separate $\ensuremath{\alpha}$ into its paramagnetic ${\ensuremath{\alpha}}_{p}$ and magnetic ${\ensuremath{\alpha}}_{m}$ components. The calculated values of ${\ensuremath{\alpha}}_{m}$ near ${T}_{C}$ were fitted to the power-law equation, ${\ensuremath{\alpha}}_{m}=A({t}^{\ensuremath{-}a}\ensuremath{-}1){a}^{\ensuremath{-}1}+B$, that describes critical phenomena near the critical temperature [$t=(T\ensuremath{-}{T}_{C}){T}_{C}^{\ensuremath{-}1}$]. It was demonstrated that the critical exponents above and below ${T}_{C}$, $a$ and ${a}^{\ensuremath{'}}$, respectively, are the same as those derived from specific-heat measurements and that $a={a}^{\ensuremath{'}}=\ensuremath{-}0.093(\ifmmode\pm\else\textpm\fi{}0.010)$ in agreement with scaling laws of critical phenomena.

Semi-empirical formulas for heavy-ion stripping data

Abstract: All available charge state measurements for heavy ions in dilute gases and carbon foils at equilibrium or near-equilibrium conditions were analyzed to improve semi-empirical formulas for the distribution parameters. Each experimental distribution was fit to an asymmetric function F/sub q/ = F/sub m/C x exp (-0.5 t/sup 2//(1 + epsilon t)), where t = (q - q/sub 0/)/rho and q/sub 0/ is the maximum intensity charge value. Subsequent fits of the resultant distribution parameters q/sub 0/, rho, and epsilon to empirical functions of projectile charge and velocity yielded rms deviations of about 0.5 for q/sub 0/, 4 percent for q/sub 0//Z, 5 to 7 percent for rho, and 0.03 for epsilon/rho. The asymmetric distribution gives substantial improvement over previous expressions for prediction of small F/sub q/ values for heavy ions in dilute gases.

Theory of ballooning modes in tokamaks with finite shear

Abstract: We studied ballooning instabilities in tokamaks of arbitrary cross sections and finite shear. These azimuthally localized, ideal magnetohydrodynamic modes have large toroidal-mode numbers, but finite variation along the field and across the flux surfaces. Stability is determined by solving a second-order ordinary differential equation on each flux surface, subject to the proper boundary conditions. Qualitative agreement is achieved with the Princeton PEST stability code.

A demonstration of one‐atom detection

Abstract: Resonance ionization spectroscopy, a photoionization method in which all of a given quantum selected species are converted to ion pairs, has been used to develop a detector for a single atom. We have demonstrated the detection of one atom by using a pulsed dye laser to photoionize Cs to saturation and a proportional counter for the detection of single electrons. Some current applications, e.g., the slow transport and chemical reactions of atoms, are briefly discussed. Future applications may include the detection of rare events such as quarks, solar neutrinos, and superheavy elements.

Electron-phonon coupling in the transition metals: Electronic aspects

Abstract: The electron-phonon coupling parameter $\ensuremath{\lambda}$ may be written as the product of three factors: the Fermi-energy density of states, $N({E}_{F})$, the Fermi-surface average of the electron-phonon interaction, $〈{I}^{2}〉$, and an effective inverse lattice force constant $\ensuremath{\Phi}$. We have calculated $〈{I}^{2}〉$ and $N({E}_{F})$ for 11 $4d$ transition-metal systems using the rigid muffin-tin approximation. We find a large but understandable variation in $〈{I}^{2}〉$ which is in good agreement with the empirical variation in $〈{I}^{2}〉$. $〈{I}^{2}〉$ varies approximately as the inverse second power of the atomic volume and as the first power of the amount of $l=3$ Fermi-energy state density within the Wigner-Seitz cell. We discuss the implications of our findings in regard to the search for systems with higher superconducting transition temperatures.

Optical properties of polystyrene from the near-infrared to the x-ray region and convergence of optical sum rules

Abstract: Optical properties of polystyrene in the form of thin films were determined for photon energies between 0.6 and 82 eV from transmission measurements. The results for $k$, the extinction coefficient, were combined with previous experimental results in the soft and hard x-ray regions up to 8050 eV. Analyses were made on several sum rules for the optical properties in this unusually wide energy range, including a sum rule for the refractive index $n$ derived recently by Altarelli et al. Redistribution of the oscillator strength corresponding to 2.7% of the total electrons was found between the valence and core excitations of carbon. Using the complex dielectric function and the energy-loss function obtained, the average photoexcitation energy and the average energy loss for fast-charged particles over the entire oscillator strength distribution were evaluated to be 25.1 and 36.8 eV, respectively.

Clinical toxicology of mercury.

Abstract: Based on an extensive literature search, general principles of mercury toxicity are outlined with respect to human individuals and populations. For the metal itself, as well as for its most important inorganic and organic compounds, the review discussed behavior in the body, characteristic clinical pictures, assessment of threshold levels, and evaluation as potential environmental hazards. Particular emphasis is placed on those diagnostic signs and symptoms which furnish early warning signals, permitting detection and elimination of overexposures.

Electron slowing-down spectra in aluminum metal

Abstract: We have studied theoretically the energy distribution of electrons generated in solid aluminum by uniformly distributed electron sources of various energies. Inelastic cross sections for energy loss and secondary electron creation are inferred from the electron-gas model for those electrons which are in the conduction band. Inner-shell excitations are treated using atomic models. Slowing-down spectra are computed for several monoenergetic sources and for ..beta.. particles from the decay of radioactive /sup 198/Au. Comparison with experimental data is made.

Experimental Measurement of Electron Heat Diffusivity in a Tokamak

Abstract: Electron temperature perturbations produced by internal disruptions in the center of the Oak Ridge Tokamak (ORMAK) are followed with a multichord soft-x-ray detector array. The space-time evolution is found to be diffusive in character, but the conduction coefficient determined from a heat-pulse-propagation model is larger by a factor of 2.5-15 than that implied by the measured gross energy-containment time.

Secondary structure of histones and DNA in chromatin

Abstract: Laser Raman spectroscopy indicates that the inner histones which are bound to DNA in chromatin or in isolated nu bodies are similar in conformation to the inner histones which are dissociated from DNA in high-salt solutions. This structure contains, on the average, 51+/-5% alpha-helix and no substantial beta-sheet conformation. It is proposed that the protein core of the nu body has a high alpha-helix content.

Observation of the Reaction H 0 + O 8 + → H + ( O 7 + ) during Neutral-Beam Injection into ORMAK

Abstract: Several lines of O viii have been investigated during the injection of hydrogen atoms at energies of 10, 15, and 30 keV into the Oak Ridge tokamak (ORMAK). The Lyman-$\ensuremath{\alpha}$, -$\ensuremath{\beta}$, and -$\ensuremath{\gamma}$ lines and the Balmer-$\ensuremath{\beta}$ line exhibit slowly increasing signals, but the intensity of the Balmer-$\ensuremath{\alpha}$ line increases sharply as soon as injection begins. This prompt signal is interpreted to be the direct result of charge transfer from hydrogen to ${\mathrm{O}}^{7+}$ ions in excited states.

The mutagenicity of hydrazine and some of its derivatives

Abstract: Hydrazine has a number of uses in industry as an antioxidant for boiler and cooling-tower water and as a source material for synthesizing a wide range of pharmaceuticals and plant growth inhibitors. Hydrazine can react with the pyrimidines in DNA to saturate the 5,6 double bond, especially of thymine; to form N4-aminocytosine; and to open up the pyrimidine ring with consequent loss of pyrimidines from DNA. It can act either directly with DNA or through intermediate radical reactions including the formation of H2O2. Some of the substituted hydrazines can also react in much the same way; others, especially the methyl derivatives, can act as alkylating agents to alkylate purines, primarily. H2O2 and the radical reactions are probably important for inactivating phage and transforming DNA treated in vitro. H2O2 is probably not important for mutagenesis in such systems, but it is likely that radical reactions are at low concentrations of hydrazine. At high concentrations direct reaction with the DNA probably predominates. The evidence suggests that both radical reactions and the direct amination of cytosine may be mutagenic for bacteria and phage treated within bacteria. Again, H2O2 does not seem to be important. The mutations produced by hydrazine are probably produced by direct mispairing at replication rather than by error-prone repair. It is not clear what the relative roles of the products of hydrazine action, N4-aminocytosine and 5,6-dihydrothymine, are in this process. Hydrazine produces mutations in higher plants and in Drosophila, but there are some unexpected features concerning time of detection and locus specificity that are not yet explained. The mutations produced by hydrazine seem to be mainly or entirely singlelocus changes. No dominant lethals are induced even though mutations are produced in bacteria in the host-mediated assay. No tests for chromosomal aberrations, other than those for dominant lethals, have been reported for this compound. Some of the derivatives of hydrazine (especially the methylhydrazine derivatives, but also some others) produce chromosomal aberrations and other chromosomal and nuclear effects. The methylhydrazine derivatives may act as alkylating agents, but the mechanism by which some of the other compounds, such as isoniazid, produce chromosomal aberrations is not clear. Hydrazine, isoniazid, and several alkyl derivatives have been reported to be positive in tests for carcinogenesis in laboratory rodents. There is as yet no evidence for carcinogenicity in humans for isoniazid, the only compound for which there is appreciable epidemiological data. The role of metabolic activation and other aspects of tissue specificity for carcinogenesis are still poorly understood.

A review of the genetic toxicology of chlorinated dibenzo-p-dioxins☆

Abstract: Information from both published and unpublished sources considered relevant to the understanding of the genetic toxicology of chlorinated dibenzo-p-dioxins is summarized in this review. Interest in writing this paper was stimulated by the fact that this class of compounds, particularly 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has gained notoriety as an extreme environmental and industrial hazard. The potential for human exposure occurs in the work place when dioxins are formed during the synthesis of a number of commercially important compounds such as 2,4,5-trichlorophenoxyacetic acid, hexachlorophene, and pentachlorophenol. Environmental contamination may result from manufacturing processes and from dioxin contaminants in marketed products. Research on dioxins as potential mutagens was initiated because of their structural similarity to acridines, a class of known intercalating agents. To date, only 4 dioxin compounds have been evaluated for mutagenicity: the di-, tetra-, and octa-chlorinated derivatives and the unsubstituted dibenzo-p-dioxin. Since only a few of the many possible structural forms of dioxins have been tested, no definite conclusions can be made about their potential mutagenicity. Furthermore, the positive mutagenicity and cytological effects reported thus far with the few dioxin isomers examined seems to depend on the position of chlorine substitution. The most active form of the molecule is the 2,3,7,8-derivative (TCDD). Data available for assessing the mutagenic potential of TCDD are conflicting and scarce. Differences in testing results reported in these studies could be attributed to solubility problems with the test chemical, treatment protocols, purity of test samples, or toxicity. Because there are conflicting data, additional experiments are needed before the mutagenic potential of TCDD and other dioxins can be determined. Studies exploring the promoting effect of dioxins on the mutagenicity of other compounds are also recommended because experiments have shown TCDD to be an extremely active liver enzyme inducing agent that enhances the mutagenicity of certain polycyclic hydrocarbons such as 3-methylcholanthrene in vitro. The importance of discerning the hazards to human health from dioxin compounds became apparent after an accidental release of TCDD from a chemical plant contaminated the Seveso, Italy area in July 1976 ∗ . This accident revealed that insufficient data were available to properly evaluate the long-term health risks posed by dioxin compounds. Several research projects were therefore initiated after the Seveso incident; it is hoped that many of the questions concerning the mutagenicity of TCDD and possibly of other dioxin congeners will be answered as a result of this work.

Divergence of metabolic activation systems for short-term mutagenesis assays.

Abstract: POLYCYCLIC hydrocarbons such as benzo(a)pyrene (BP) are prevalent environmental contaminants3 and are increasingly suspect as human carcinogens. They are routinely used as tumour agents in laboratory animals1 and in tissue culture assays2. These compounds are produced by the incomplete combustion of carbonaceous material such as fossil fuels used for transportation and industrial energy production. They are biologically inactive as parent compounds and require metabolic activation in tissue to produce a tumourigenically active species of the molecule. Activation is accomplished through the drug metabolising monooxygenase enzymes containing cytochrome P450 (refs 4–6), and activate the parent carcinogen to an intermediate epoxide7,8 which readily alkylates cellular macromolecules.

Fundamental cryobiology of mouse ova and embryos.

Abstract: An increasing fraction of mouse ova and embryos are killed as the rate at which they are cooled to -196/sup 0/C is increased. The survival of these cells depends not only on cooling rate, but also on the minimum subzero temperature to which the cells are cooled. Low temperature microscopy demonstrates that lethal cooling rates are coincident with those that produce intracellular ice formation, and that the lethal temperature appears to be that at which intracellular ice forms. Furthermore, the microscopy shows that ova do not dehydrate when cooled at rates that produce intracellular ice and cell death, but undergo substantial shrinkage when cooled at rates that produce little intracellular ice and high survival. Measurements of the water permeability of mouse ova and the temperature coefficient of that permeability can be used to test a mathematical model formulated to describe the kinetics of water loss at subzero temperatures from a hypothetical cell. The observed dehydration of ova cooled to subzero temperatures at given rates is approximately predicted by the mathematical model, although there is some quantitative discrepancy between the observed and calculated responses.

One-atom detection using resonance ionization spectroscopy

Abstract: A new measuring technique which can detect a single atom of a given kind, even in the presence of ${10}^{19}$ or more atoms of another kind, with good space and time resolution, was utilized to study the density fluctuation of less than 100 cesium atoms in a small volume of space filled with inert gases. Repeated measurements of the absolute number of atoms in a defined volume at an arbitrary time were recorded for the first time in order to obtain a statistical distribution giving the fluctuation of the number of atoms around the mean value. Numerous other physics applications of the one-atom detector are briefly described.

Surface Scattering from W Single Crystals by MeV He + Ions

Abstract: The surface peak, observed in backscattering-channeling experiments, has been measured as a function of projectile (He/sup +/) energy on a clean W(100) crystal. We show that the intensity of the surface peak is in good agreement with classical models of channeling. Furthermore, we deduce an upper limit of 6% for the relaxation of the W(100) surface.