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In this work, we monitor the onset of nonthermal melting in single-crystal silicon by implementing an x-ray pump-x-ray probe scheme. Using the ultrashort pulses provided by the Linac Coherent Light Source (SLAC) and a custom-built split-and-delay line for hard x rays, we achieve the temporal resolution needed to detect the onset of the transition. Our data show no loss of long-range order up to 150±40 fs from photoabsorption, which we interpret as the time needed for the electronic system to equilibrate at or above the critical nonthermal melting temperature. Once such equilibration is reached, the loss of long-range atomic order proceeds inertially and is completed within 315±40 fs from photoabsorption.

Direct measurement of plutonium and uranium X-rays and gamma-rays is a highly desirable non-destructive analysis method for the use in reprocessing fuel environments. The high background and intense radiation from spent fuel make direct measurements difficult to implement since the relatively low activity of uranium and plutonium is masked by the high activity from fission products. To overcome this problem, we make use of a grazing incidence optic to selectively reflect K α and K β fluorescence of Special Nuclear Materials (SNM) into a high-purity position-sensitive germanium detector and obtain their relative ratios.

Equilibrium contact angles are reported for silicone oils (poly(dimethylsiloxane)s) on polymer-coated and uncoated solid-silicon substrates immersed in aqueous electrolyte solutions. Solid-substrate wettability to water ranges from highly hydrophilic to highly hydrophobic based on water/air contact angles. Although silicone oils in air spread completely on all of the studied substrates, these same surfaces when immersed in aqueous media exhibit finite contact angles against silicone oils that depend strongly on the substrate surface energy. A detailed investigation of the pH influence on the wetting behavior of silicone oil on the solid substrates is pursued where a clear correlation emerges between the changes of substrate-surface zeta potential (ζ) and the oil-wetting behavior on substrates immersed in aqueous solution. Also, the influence of inorganic KCl and CaCl2 electrolytes on the wetting behavior of silicone oils on solid substrates is studied. KCl does not produce a noticeable effect on the wetti...

At the Lawrence Livermore National Laboratory (LLNL) we have engineered a silicon prototype sample that can be used to reflect focused hard x-ray photons at high intensities in back-scattering geometry.1 Our work is motivated by the need for an all-x-ray pump-and-probe capability at X-ray Free Electron Lasers (XFELs) such as the Linac Coherent Light Source (LCSL) at SLAC. In the first phase of our project, we exposed silicon single crystal to the LCLS beam, and quantitatively studied the x-ray induced damage as a function of x-ray fluence. The damage we observed is extensive at fluences typical of pump-and-probe experiments. The conclusions drawn from our data allowed us to design and manufacture a silicon mirror that can limit the local damage, and reflect the incident beam before its single crystal structure is destroyed. In the second phase of this project we tested this prototype back-reflector at the LCLS. Preliminary results suggest that the new mirror geometry yields reproducible Bragg reflectivity at high x-ray fluences, promising a path forward for silicon single crystals as x-ray back-reflectors.

Bragg mirrors can be used to direct a free-electron laser's x-ray beam onto a sample, but the mirrors are extensively cratered by the intense beam. To create a mirrored surface that is reproducible from one laser shot to the next, the authors in this work lithograph micropillars from a single mirrored crystal of silicon, and demonstrate a strategy whereby each shot of the laser reflects light from one pillar surface, and a fresh micropillar would then be indexed into position for the next shot.

Cellulose fibres and particles in the form of powder, tablets and paper sheets have been investigated by very low frequency dielectric spectroscopy using a novel form of dielectric cell, in which two planar electrodes have been mounted in fixed positions at right angles. The broad pattern of response obtained from the samples is independent of the structural form of the cellulose sample, a loss peak in the 0.1–100 Hz range, and at lower frequencies a dispersion process which is dominated by an imperfect charge transport. Moisture has a significant influence on the rate of charge transport. In dry samples the dipolar loss peak was not evident but as the moisture content increased it appeared. Using a humidity normalizing technique the dielectric response for microcrystalline cellulose has been characterized over the equivalent of 14 decades in frequency. It has also been shown that there is a linear response between the capacitance and the density of microcrystalline cellulose samples. The consolidation of powder into tablets is discussed with respect of the observations of changes in capacitance, loss peak frequency and imperfect charge transport efficiency. Furthermore it was found possible to investigate differences between the dipolar relaxation rate “in” and “out” of the plane of paper in the stack. The relaxation time for dipoles “out” of the paper plane is 7 to 8 times longer than for dipoles “in” the paper plane.

Four lamellar based phases in the lecithin/water/oil phase system have been prepared and examined by low-frequency dielectric spectroscopy in the frequency range 3 × 10 −5 to 3 × 10 +5 Hz. The dielectric properties of the lamellar and liquid crystal phases have been determined over ranges of temperature, and measurements are reported for mixed phase systems. From this information the physical basis for the observed responses has been determined and is reported. Two broad patterns of dielectric response have been found. The ordered micellar and liquid crystal phases do not support dc conductances, even at the lowest frequencies used. The dispersions in these well-defined phases are of the fractional power law form, ( i ω) −s , in frequency with 1 > s > 0.5 at the lowest frequencies and 0.5 > s > 0 in the hertz and kilohertz ranges. On the addition of decane, or by using a formulation that lies close to the lamellar/liquid crystal phase boundary, dc conduction is observed, but in both cases the charge transport is blocked by electrode barrier layers and the generalized Maxwell–Wagner response is found. When the conductance is brought about by the addition of the oil, a large dipolar-like dispersion is observed in the frequency range below the inverse of the bulk relaxation time of the system. This dispersion has been associated with the discrete oil globules within the lamellar structure.

Many cationic surfactants form, in the presence of certain organic acids, large supramolecular micellar structures in water. The dielectric response of one such system (cetyl trimethyl ammonium bromide-salicylic acid, CTMAS) has been studied as a function of frequency, concentration and temperature. The results are compared with dynamic mechanical data on the same system, which has been published in the literature.

Steady-state space-charge and field distributions in insulators with needle-plane electrodes have been examined theoretically by making use of hyperboloid geometry and a relaxed version of Deutsch's assumption. An analytical solution has been obtained for the conventional space-charge boundary condition of infinite charge and zero field at the surface of the charge injecting needle contact. This solution has been extended to cover a range of injection boundary conditions of both space charge and electrical field magnitudes. It has been found that, in the bulk of the material, the forms of the space charge and field distributions are relatively insensitive to the injection conditions. The distribution of power density dissipated under complete space-charge limited current flow is reported and it has been found that a maximum in the power occurs close to, but not at, the needle tip.

Collisions with rare-gas atoms are observed to produce a lengthening of the lifetime of the highly excited ($n=5\ensuremath{-}10$) $d$ states of Na. The effect is interpreted as collisional angular momentum mixing of the $d$ state with $lg2$ states; thus the average lifetime of all states for which $lg~2$ is observed. The cross section for the process appears to increase as the geometrical cross section of the excited atom.

Dielectric spectroscopical investigation of an oil in water emulsion in the frequency range from mHz to kHz has shown that the response below about 1 Hz is dominated by the physical barriers formed by the lecithin emulsifier whereas the aqueous bulk properties of the emulsion control the response above 1 Hz. Unlike the more complex gel systems already examined using this technique the ac response of the emulsion can be characterized by only five physical parameters, i.e., a high-frequency ac conductance in parallel with a capacitance, the magnitude and fractional power law exponent of the barrier capacitance, and the barrier leakage conductance. This has allowed semi-quantitative assessment of the roles of the individual constituents of the emulsion and the effect of introducing a substituted phenol to the system. The technique has been found particularly useful in observing the stability of the system to both temperature cycling through the freezing point and exposure to air.

The use of blocking layers of insulators to remove leakage current during measurement of the capacitive properties of coatings is examined both theoretically and experimentally. It is shown that in the case of vinyl emulsion films the 'leakage' is an inherent component of the response and its blocking results in a Maxwell-Wagner response with a peak in the loss component, which can be interpreted as due to charge dipoles. Furthermore, it is shown that a Cole-Cole dispersion results when the response of the film is of a power law form in the region of the Maxwell-Wagner peak loss.

The effect of high electrical fields on the drift mobility of carriers in amorphous semiconductors is examined. From Tabak's measurements of the hole mobility in amorphous selenium it is inferred that two froms of localised centres are present, shallow trapping characteristics being obtained in a relatively high temperature region and at lower temperatures an additional effect due to acceptor-like centres. These acceptor-like centres are also observed in the splat cooled vitreous selenium investigated by Marshall and Owen, and in this material the electron mobility measurements of Marshall and Miller indicate the presence of donor-like centres. Une analyse critique est donnee de l'effet des champs eleves sur la mobilite de drift de porteurs dans les semiconducteurs amorphes. En partant des mesures de Tabak sur la mobilite en Selenium amorphe on constate la presence de deux genres de centres localises. Aux temperatures eleveees il y a les effets de piegeage tandis qu'aux plus basses temperatures les centres accepteurs sont importants. Les měmes accepteurs sont observables dans les echantillons prepares par la methode de “splat cooling” par Marshall et Owen dans lesquels les mesures de mobilite par Marshall et Miller donnent l'evidence de la presence des centres donneurs.

The drying of latex paint films in a natural environment has been followed by measurements of the AC conductance of the films. Three stages in the drying have been observed with the first two being related to evaporation of water from the bulk of the film, in accordance with mechanical measurements. The third and final stage has been characterised by a power-law decay in the conductance and has been interpreted as the elimination of a percolation network as particles coalesce, thereby cutting the conduction paths.

As part of a kinetic study of XeF laser media, we have followed the time evolution of the Ne*, F*, and F*2 densities in e‐beam excited Ne/Xe/NF3(F2) mixtures. The Ne* and F* densities were monitored by laser absorption while the F2* was observed in emission at 158 nm. Rate coefficients for the quenching of these excited states by Ne, Xe, NF3, and F2 have been determined. The radiative lifetime of the F2* was measured to be 41±4×10−9 sec.

Using two- and three-photon resonance techniques, we have observed $d\ensuremath{-}g$ and $d\ensuremath{-}h$ transitions in the $n=13 \mathrm{to} 17$ states of sodium. The results yield accurate values for the quantum defects of the $d$, $f$, $g$, and $h$ states as well as the fine-structure splitting of the levels. Although the $d (l=2)$ fine structure is inverted, for $lg2$ the fine structures are observed to be hydrogenic.

An examination of the experimental behaviour of the regression of equilibrium fluctuations is made and compared with a range of theoretical models. In this basis it is suggested that the regression path is determined by a few simple rules. These are, an initial conservative-type distribution of information over a self-similar hierarchy, which is superceded eventually by a dissipative process which also proceeds in a self-similar manner. The relationship of these rules to a time-dependent evolution of the average configuration entropy is discussed and their correspondence to the fading of memory outlined. An equation of motion for the probability of realisation of the fluctuation is presented which reflects these considerations and is valid over the complete time range from initiation to equilibrium.

A discussion is given elaborating some salient features of a recently proposed many-body theory of dielectric relaxation in solids. It is pointed out that orientational polarisation involves disorder as an essential element and this leads to important conclusions regarding the relaxation processes. Three types of transitions, outlined in the original theory, are discussed in some detail and distinctions are made between “large” and “small” transitions. The physical nature of correlated states is discussed and some comments are made about energy loss processes involved in the many-body model of dielectric relaxation, with particular reference to the frequency-independent ratio of energy lost per cycle to energy stored in polarisation. In einer Diskussion werden einige herausragende Zuge einer kurzlich vorgeschlagenen Vielteilchen-Theorie der dielektrischen Relaxation in Festkorpern herausgestellt. Es wird gezeigt, das Rich-tungspolarisation Fehlordnung als ein wesentliches Element einschliest, was zu bedeutenden Schlusfolgerungen fur den Relaxationsprozes fuhrt. Drei Arten von Ubergangen, die in der ursprunglichen Theorie aufgestellt wurden, werden ausfuhrlich diskutiert und es wird zwischen „groDen” und „kleinen” Ubergangen unterachieden. Die physikalische Natur von korrelierten Zustanden wird diskutiert und es werden einige Bemerkungen uber die Energieverlustprozesse gemacht, die in dem Vielteilchenmodell der dielektrischen Relaxation auftreten, insbesondere uber das frequenzunabhangige Verhaltnis des Energieverlusts pro Zyklus zur Energie, die in der Polarisation gespeichert ist.

The effect of thermal history on the solid state phases of M.B.B.A. is investigated by examining the dielectric response of the solids formed by slow cooling the isotropic and nematic liquid crystals. In addition the relationship of these states to a glass is examined by studying the dielectric response of the quenched nematic liquid crystal.

A generalisation of Mott's model of an amorphous solid is used to investigate the characteristics of carrier transport by hopping in an extended temperature range. It is shown that three types of behaviour can be expected, the Mott T−-1/4 variable-range hopping at low temperatures, nearest-neighbour hopping at high temperatures and low hop site densities, and a weakly temperature-dependent long-range hopping at high densities and high temperatures. Criteria for the observation of these three regions are established and the transitional behaviour of the conductivity is determined. A number of experimental observations of hopping transport are examined and analysed in terms of the densities of localised states.

The electrical properties of a sample of natural molybdenum disulphide have been examined using an AC with DC bias technique It is shown that the conductance of the sample is limited by the presence of a surface layer barrier and that because of the small potential of this barrier moderate applied voltages can make it collapse to give a voltage-saturated conductance.

The prompt emission in the 225–290 nm region from atmospheric pressure laboratory air excited by a high current pulsed e beam includes a large number of bands from the Gaydon–Herman and fourth positive systems and from several other N2 band systems. The strongest of these midultraviolet features have fluorescence efficiencies of about 5×10−7, which is 1% of the value for the strongest air fluorescence feature at 337.1 nm.

Les donnees publiees sur la reponse mecanique d'une serie d'echantillons prepares a partir d'un lot unique de polyisobutene sont examinees et trois processus de relaxation/retardement sont caracterises dans la region de temperature au-dessus de la transition vitreuse

We report in this paper the observation of optical emissions from triatomic rare gas halide molecules formed in excited high density rare gas–halogen mixtures. The broad‐band continuum emissions are identified as transitions between ionically bonded excited states (Rg+2X−) and repulsive covalent lower states that dissociate to ground state atoms. These emissions become predominant at high rare gas densities.

The collisional angular-momentum mixing of $n=5\ensuremath{-}15$ Na $d$ states with the $lg2$ states of the same $n$ has been studied using He, Ne, and Ar as collision partners. At rare-gas pressures of \ensuremath{\sim}1 Torr, the $l\ensuremath{\ge}2$ states are thoroughly mixed and the mixture decays at the average radiative lifetime of all the $l\ensuremath{\ge}2$ states of the same $n$. Using \ensuremath{\sim}1 Torr of neon to collisionally mix the $l\ensuremath{\ge}2$ states, the average lifetime for $l\ensuremath{\ge}2$ was measured for each $n$ and compared to the theoretical prediction for hydrogen, with which it is in excellent agreement. The cross section for $l$ mixing by each of the gases is found to increase sharply from $n=5 \mathrm{to} 10$ and decrease above $n=10$. The magnitudes of the $l$-mixing cross sections are found to correlate with the low-energy scattering lengths of the collision partners.

A series of heterogeneous gels, prepared by the interaction of cetostearyl alcohol and cetrimide, together with an emulsion and a sample of gel that had undergone structural changes on storage have been used to illustrate the manner in which a detailed dielectric analysis may be used to deduce complex structural information about these heterogeneous systems. The data have been discussed in terms of a model proposed by the authors and based on the concept of self-similarity in the gel structures. Here the dielectric information is compared to the structural differences between the samples observed using freeze-fracture scanning electron microscopy.

Liquid egg white was concentrated by ultrafiltration (UF) or reverse osmosis (RO) using a Damrow PCI system (Fond du Lac, Wisconsin). After concentration, the egg white was spray dried in an Anhydro (Copenhagen, Denmark) spray drier. The UF treatment of egg white significantly (P

The dielectric properties of a range of plant foliage have been examined in the frequency range between 10−2 Hz and 104 Hz. The results are reported and analyzed in terms of circuit combinations of dispersive dielectric elements. In all cases some type of charge transport contributed a component to the combination, but apart from some of the evergreen samples this component was not that of a frequency-independent de conductivity. For both the annual and deciduous plant leaves the principal transport process was found to have the frequency dependence characteristic of ‘quasi-dc transport’, and this process dominated the observed dielectric disperison in these samples. The observed behaviors are discussed in terms of the known properties and structure of leaves and it is shown that the dielectric technique can be a useful and informative investigative technique in these complex systems.

The temporal and spectral behavior of absorption in the visible by e -beam excited argon, krypton, and xenon have been investigated with and without additives. The probe light used was from an argon-ion pumped, tunable dye laser, or from the visible lines of the argon-ion laser itself. Strong absorption was observed at all wavelengths investigated (450-620 nm). Structured absorptions out of atomic and molecular excited states have been identified by their temporal, spectral, and pressure behavior. The ubiquity of these absorptions, which is not fully understood, should have serious implications for the development of new visible lasers that operate during the electron-beam pumping pulse.

A number of thin aggregated metal films on glass substrates are analysed in terms of the model proposed earlier (Hill 1969). It is shown that the model is consistent, and that the conductivity of a thin metal film forming an island structure can be defined in terms of the island size and spacing, and of the properties of the substrate and the film material. The potential barrier heights for electron tunnelling between particles of gold, particles of platinum , and particles of silver through soda and barium aluminosilicate glass have been determined. It is shown that the bias effect in thin metal films (Hill 1964 a ) can only be observed with metals of work function close to that of the substrate material and when the substrate contains free alkali ions.

The increase in adhesion obtained for aluminium films by the pre-deposition of films of chromium is investigated, using Heavens' method of adhesion testing. It is found that the adhesion varies with the thickness of the chromium film, and with time. The variation with time suggests that the nature of the increase in adhesion is primarily one of alloying at the metallic interface, and subsequent age-hardening.

Thin layers of nickel, cobalt and chromel are evaporated under vacuum on to glass microscope slides and used as underlayers for aluminium films. Adhesion measurements are used to investigate ageing effects which are shown to depend upon temperature as well as the nature and thickness of the underlayer. Results are shown to be due to intermetallic compound formation at the interface causing a type of age-hardening which may result in either decrease or increase in the measured adhesion according to the compound formed and the condition of ageing.

Electrical conduction in Nb/${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ cermet films at low temperatures shows the presence of a new form of hopping conduction through localized states. In this mechanism the dielectric plays an essential role, behaving like an amorphous wide-band-gap semiconductor and acting as host to a distribution of localized states due to Nb dispersed, on an atomic scale, in the alumina matrix.

The infrared absorption spectrum of KH2PO4, KD2PO4, and KH2AsO4 single crystals has been measured from 3000‐1000 cm−1 over a temperature range from 20°‐300°K. Three broad absorptions are found at 2670, 2360, and 1720 cm−1 which are associated with the hydrogen bonds. The two upper frequencies are stronger for light polarized perpendicular to the polar axis but are also found for light polarized along the polar axis. These absorptions have counterparts in the deuterated crystal with a frequency ratio νH / νD≃1.35. The lower‐frequency absorption is strongest for light parallel to the polar axis and shows intensity changes at the Curie temperature, accompanying the appearance of a sharper absorption at 1850 cm−1 which has a Curie‐law behavior above Tc. It is concluded that the uncoupled hydrogen‐bond vibrations which give rise to the absorption at 2670 and 2360 cm−1 show no observable splitting of the ground or first vibrational state. This eliminates a double minimum potential with appreciable tunneling bet...

Calculations of state functions in equilibrium plasmas produced behind shock-waves in potassium and caesium vapour are described and the results are presented graphically. For a given initial temperature T1 of the saturated vapour and a given Mach number M of the incident shock, the temperature, density and degree of ionization behind both the incident and reflected shocks were calculated from the Rankine Hugoniot relations and the Saha equation over the range 3

Measurements of adhesion have been made on films of silver, gold, copper and aluminium with under layers of chromium. The films have all been deposited on glass microscope slides by vacuum evaporation and the adhesion has been measured by drawing a smoothly rounded point across the surface whilst increasing the load on the point until a clear, well-defined channel was produced. It has been shown that in the case of bimetallic films, abnormally high figures may be obtained due to the formation of an intermediate layer by diffusion or intermetallic reaction. The results show a dependence upon the thickness of the chromium underlayer and time as well as upon the metal of the upper layer. Explanations are based upon a structural model for chromium films which assumes an aggregated structure formed of oxide-coated particles below 400 A thickness and a continuous metallic structure above this thickness. It is shown that intermediate layer formation occurs only when the thickness of chromium exceeds 400...

Measurements of colloid osmotic pressure and refractive index of five species of teleost fishes are recorded. A number of observations were made on eels which had been starved for two months. With the exception of the eel, the colloid osmotic pressures were less than half the characteristic level for mammals, the average being about 100 mm. H2O. Normal eels showed serum colloid osmotic pressures within the mammalian range, the starved eels showed values less than half as great but showed no signs of oedema. A comparative table of colloid osmotic pressures for the vertebrates studied so far is presented. The relation between refractive index and the colloid osmotic pressure is discussed briefly.

We present an analysis of optically pumping Rydberg states in alkalis to generate coherent lasers in the infrared and far‐infrared spectral regions. Based on the previous accurate experimental and theoretical data on these states, our conclusion is that such laser systems can be operated either pulsed or cw and possess narrow linewidths, high gains, and considerable tunability. Wavelengths near 16, 12, 8.6, and 7.7 μm which are of interest for isotope separation are achievable with milliwatt power levels. Specific examples for Na vapor are given.

Ar/Xe/NF3 mixtures were excited by the focused beam from an ArF (193 nm) laser. Xe+ ions are produced by two‐photon ionization, the electrons attach to make F−, and the ions recombine to make XeF*. Radiation is observed in the XeF(B 1/2) →XeF(X 1/2) bands near 351 nm and in the broader XeF(C 3/2) →XeF(A 3/2) band near 460 nm. At low background gas pressure, mostly B‐X uv emission is observed. As the argon pressure is increased to 1000 Torr, the visible/uv band intensity ratio increases to about 3 to 1. We conclude from these results that the C (3/2) state lies 700±70 cm−1 below the B (1/2) state. This conclusion should have a significant impact on our understanding of the fluorescence yields and laser performance of e‐beam‐excited XeF.

We have observed intense band emissions between 340 and 344 nm from electron‐beam‐excited mixtures of high‐pressure argon gas and iodine vapor. This emission appears to be from molecular iodine. Using the 357.6‐nm band from an Ar/N2 mixture as a calibration, we have measured the fluorescence yield in this wavelength region to be 70±24%. From this we computed an over‐all fluorescence energy efficiency of 13±4%. Based on these observations, we suggest the feasibility of an efficient high‐energy electron‐beam‐pumped argon‐iodine laser. The gain of such an argon‐iodine laser should be comparable to that of the Ar/N2 second positive laser.