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The design and operating characteristics of the VUV undulator installed on the NSLS VUV ring are presented. Specifically, the spectral output through three circular on-axis pinholes of different diameters has been measured. Near the minimum magnetic gap (40mm), the flux into a 0.25 mrad circular aperture at the peak of the fundamental (h..nu.. = 57 eV) is approx.1 /times/ 10/sup 14/ photonssec0.1A1%BW. We find good agreement in spectral shape between these measured spectra and spectra calculated by integrating the theoretical undulator emission spectrum over the relevant spatial variables and including electron beam emittance. We also show calculated zero-emittance and on-axis flux spectra for comparison. A description is given of the beam line and monochromator currently installed on this undulator for the purpose of performing spin-resolved photoemission.

We present k-resolved inverse photoemission spectroscopy (KRIPES) results for Ag(111) in the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} K\ifmmode\bar\else\textasciimacron\fi{} direction of the surface Brillouin zone. The spectra were taken as a function of electron energy and angle of incidence at a fixed photon energy (9.7 eV) of the emitted radiation. The crystal-induced surface state and the image-potential-induced surface state are observed with final-state electron energies at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} in good agreement with a recently proposed multiple reflection model and with dispersion characterized by effective masses ${m}^{\mathrm{*}}$=0.7m and ${m}^{\mathrm{*}}$\ensuremath{\approxeq}m, respectively. The measured intensity of the surface state roughly follows a ${\mathrm{cos}}^{2}$\ensuremath{\alpha} dependence, where \ensuremath{\alpha} is the angle between the sample normal and the polarization vector of the detected photons. Transitions into bulk-derived final states are observed, with final-state electron energies ranging from ${E}_{F}$ to ${E}_{F}$+20 eV. The dispersions of these bulk-derived final states agree with very simple ``empty-lattice isochromats'' derived from free-electron bands of proper symmetry, as well as with results of a band-structure calculation based upon a combined interpolation scheme.

Basal-plane surfaces of single crystal samples of La 2 CuO 4 , parent compound of a class of high T c superconductors, are found to display a 1 × 1 LEED pattern which converts to a 1 × 8 pattern after annealing. The superlattice is attributed to chains of ordered oxygen vacancies. Auger spectroscopy suggests that in the 1 × 8 configuration the crystal prefers to terminate with a Cu-O rather than a La-O plane.

We compare new high-resolution inverse-photoemission spectra of the unoccupied surface states on Cu(001) with a first-principles calculation of the same surface. This theoretical calculation includes the asymtotic long-range image potential. The commonly observed image state is found to correspond to the n=1 member of the Rydberg series of states derived from the image potential, i.e., the wave function has a single extremum beyond the crystal edge characteristic of the hydrogenic n=1 state. Agreement between theory and experiment for all states is excellent. The experimentally determined binding energies and effective masses are 0.62 eV and 0.98${m}_{e}$ for the n=1 image state and 0.8 eV (with respect to ${E}_{F}$) and 0.4${m}_{e}$ for the n=0 surface resonance. The results indicate that surface corrugation effects are negligible.

Momentum-resolved inverse photoemission spectra have been taken on Pd(111) at h..omega.. = 9.7 eV. In addition to the unoccupied part of the d band, we observe an s,p peak which disperses, but lies somewhat higher in energy (by approx.0.5 eV) than a bulk direct-transition peak predicted by band-structure calculations. The s,p peak does not fall in the fundamental s,p gap, and is therefore not attributable to a surface state. A step structure close to the vacuum level is attributed to band-gap emission and image-potential states.

Single crystals of lanthanum cuprate have been studied using k-resolved inverse photoemission. The predicted dispersion of the Cu 3d--O2p-derived band through the Fermi level is not observed and this may influence models for high-temperature superconductivity based on band-structure calculations. In addition, resonant inverse photoemission of the lanthanum-derived features is also observed at the plasmon frequencies.

Inverse photoemission spectra on Pd(110) reveal bulk band-structure features, and surface-state features in the projected gaps centered at points Y-bar and X-bar. The energy dispersion of the bulk band-structure features is in agreement with direct-transition predictions. Surface-state energies and their dispersion are reproduced with a nearly-free-electron model and a surface-barrier model which places the image plane 2.3 a.u. beyond the outermost atomic layer. The experimentally determined energies of surface states are as follows: at point X-bar, 6.6 eV above E/sub F/, designated S/sub 0//sup +/; at point Y-bar, 3.4 and 6.6 eV above E/sub F/, designated S/sub 0//sup +/ and S/sub 1//sup -/, respectively.

New insight into the bonding of carbon monoxide with transition-metal-surfaces is provided by spin-polarized photoemission studies of CO on Fe(001). The interaction of the molecular 5{sigma} levels with the substrate {ital d} bands is found to be very weak for both tilted and vertical CO species. The former shows clear evidence for a {pi}-{ital d} band interaction with discrete spin-polarized features in the occupied {ital D} band; the latter shows only small changes. Inverse photoemission studies (non-spin-polarized) indicate that the unoccupied 2{pi} level is closer to the Fermi level for the tilted CO species.

Measuring the photoelectron branching ratios of the outer and inner valence emission of ethylene as a function of photon energy between 40 and 200 eV, we are able to identify the various photoemission lines. As theory predicts, the single particle picture breaks down for the innermost valence orbital (2a g ). The photoemission from this orbital is spread over two lines which are also degenerate with other excited state configurations of the ion. This leads to interference effects which are indeed observed in the cross section of these lines.

The effect of the crystalline field on the spin-orbit interaction of the $^{3}P^{\ensuremath{\circ}}$ and $^{1}P^{\ensuremath{\circ}}$ states of ${\mathrm{Tl}}^{+}$ in KCl has now been included in the configuration coordinate model. The potential energy curves for the pure spin states are required to satisfy the condition that after the application of spin-orbit interaction the resulting crystal states account for the absorption and emission spectra, explained by the earlier model, and for the oscillator strengths of the absorption bands. In accordance with the adiabatic approximation, the potential energy curves for the states involved in absorption and emission do not cross and the electronic matrix elements for radiative transitions depend on the configuration coordinate. The curve for the lower excited state has two minima which account for the 3050 A and the 4750 A emission bands. From the single minimum of the upper excited state an additional emission band near the 2470 A absorption band is predicted. With intense excitation at 77\ifmmode^\circ\else\textdegree\fi{}K in a narrow spectral range near 1960 A, which corresponds to excitation only to the upper excited state, the predicted emission has been found. The existence and characteristics of the new emission provide confirmation of the model, particularly of the quantitative effect of spin-orbit interaction.

Frog sartorius muscle was loaded with a small cup to which mercury could be added or removed with a motor-driven syringe to achieve dynamic loading cycles. Intermittent stimulation during the loading and unloading cycle very significantly reduced the creep of the resting muscle. Analysis of the data indicates that contraction acts to reset the resting length of the muscle system as well as evoke the contractile response. On the basis of the available evidence, it is suggested that a resetting of the cross linkages between the myosin rods and the actin filaments during contraction is the most plausible explanation of this interaction between the contractile mechanism and the viscoelastic state of the resting muscle.

The effects of activator concentration, added impurities, infrared stimulation, and temperature of excitation on the thermoluminescence of KCl:Tl permit the identification of the two principal trapping levels as the 3P00 and 3P20 states of isolated Tl+. The energy of activation necessary to fill these metastable states, following excitation to the 3P10 and 1P10 states, is provided by the polarization energy. The concentration of traps simultaneously filled is limited primarily by re‐excitation of metastable Tl+. F and V centers are created by multiple excitation of Tl+. These interpretations are quantitatively correlated by a configuration coordinate model and are shown to be in accord with the band theory.

The dependence of spectral distribution and intensity of emission of KCl: Tl on temperature and excitation wavelength are correlated with absorption data and theoretical calculations to provide a detailed picture of the energy relationships in this phosphor. The two principal excited states are the 1P10 and 3P10 states of Tl+ and are found to be approximately in thermal equilibrium with each other. The equilibrium is disturbed by emission, and the 4750A emission is favored by 1960A excitation and the 3050A emission is favored by 2470A excitation. The former processes are attributed to 1P10↔1S0 transitions; the latter, to 3P10↔1S0 transitions. The rate processes are formulated and the specific rate constants deduced. The presence of Tl+ or Cd++ adjacent to the activator induces additional excitation and emission bands. The activation energy for radiationless de‐excitation has been computed theoretically and found to be in accord with experiment.

A spin-resonance center whose concentration is sensitive to x irradiation has been observed in synthetic calcium fluorophosphate crystals. It shows an electron spin of 1/2 and hyperfine interaction with two equivalent F/sup 13/ nuclei. Arguments are presented which lead to its identification as an O/sup -/ ion occupying an F/sup -/ site. (auth)

The specific susceptibilities of a series of manganese‐activated zinc fluoride phosphors and their components have been measured. The unexcited manganese was found to be in the divalent 6S state. There is evidence for exchange demagnetization of adjacent paramagnetic activator ions.The change in paramagnetic susceptibility with excitation, predicted by Williams and Eyring [F. E. Williams and H. Eyring, J. Chem. Phys. 15, 289 (1947)] to explain the long non‐temperature‐dependent lifetimes of the emitting states of luminescent solids containing paramagnetic activators, has been measured for manganese‐activated zinc fluoride. Radiation from a high voltage discharge lamp was used to excite the phosphor in a vacuum magnetic balance having a sensitivity of 10−6 dyne per mm scale deflection. The observed change in susceptibility corresponds to a decrease of the order of magnitude of one Bohr magneton per excited activator ion.

Oscillator-strength ratios for the two principal impurity absorption bands of KCl: Tl and KCl: In are calculated including the effect of crystalline interactions. The phosphor KCl: In was devised in order to provide an additional check of the theoretical analysis. The excited impurity states are assumed to be of the nature of $^{1}P^{0}$ and $^{3}P^{0}$ states of the $\mathrm{sp}$ configuration mixed by spin-orbit interaction. Spin-orbit coupling constants are obtained from free-ion spectra. Crystal interactions are included by using experimental transition energies for the crystal to calculate the energy separation of the pure singlet and triplet states in the crystal. The calculated oscillator-strength ratios are in satisfactory agreement with experiment.

The previously published analysis (see reference 1) of the dependence of efficiency of substitutionally activated inorganic phosphors on activator concentration is generalized to include a wide variety of inorganic phosphors under various types of excitation. In addition to the optical excitation of the activator, the creation of conduction electrons and excitons, and the transfer of their energy to the luminescent and non‐luminescent activator ions and to other impurities and lattice defects are included in the formulation. The dependence of efficiency on activator concentration of ZnF2:Mn under c.r., x‐ray, vacuum u.v. and near u.v. has been measured and interpreted on the basis of the theory. Preliminary photo‐conductivity measurements clarify the role of the conduction band in the luminescence of ZnF2:Mn. Also the dependence of the efficiency vs. activator concentration of both ZnF2:Mn and KCl:Tl on temperature has been measured and interpreted on the basis of the variation in activation energy for competing radiationless processes with distance between activator ions. In addition, other efficiency vs. activator concentration data previously published by other authors (see reference 8) on a variety of phosphors and at various temperatures can be correlated and explained with the general theory.

Single crystals of ZnF2: Mn have a single symmetrical thermoluminescent peak when excited by monochromatic radiation of wavelength 1800 to 2300 A. The electron trap responsible for this peak is a metastable state of the activator. Excitation occurs first to a higher excited state from which both the emitting and trapping states are accessible. With 1850 A excitation, transfer to the emitting state from the initial excited state is approximately 4 times as probable as transfer to the trapping state. Untrapping occurs by a monomolecular process modified by thermally activated retrapping from the state governing the rate of emission. Energy level diagrams are proposed for the states of Mn++ responsible for absorption emission and trapping.

The specific magnetic susceptibilities of manganese‐activated zinc fluoride phosphors of diverse activator concentration, and prepared by various crystallization procedures, have been measured from −60°C to 200°C. A trivial Weiss constant, except for phosphors of inordinately high manganese concentration, demonstrates the absence of appreciable exchange demagnetization of adjacent paramagnetic activator ions and suggests that there exists negligible departure from a random distribution of manganese ions over cation sites. Utilizing this distribution, and recognizing that only manganese ions not having other manganese ions at any of the nearest cation sites are capable of luminescence, an expression for the dependence of luminescent efficiency on activator concentration is derived and found to be in quantitative agreement with experiment.

On considere des fonctions a valeurs reelles a plusieurs variables. On presente des sous-ensembles de l'intervalle I qui forcent analyticite ou la polynomialite. Ensemble de suites forcant l'analyticite ou la polynomialite

We have identified a new unoccupied surface resonance approximately 1.15 eV above the Fermi level on Cu(001) with the use of inverse photoemission. The resonance has to be separated from a nearby intense peak due to a bulk direct transition. This has been done in two ways: (a) varying the photon energy, which causes a shift in the bulk peak, and (2) varying the work function, wich causes a shift in the resonance. The occurrence of the resonance is consistent with a recently proposed phase analysis.

The intensities of the Cd 2288‐ and 2981‐A and Cd+ 2144‐ and 2265‐A lines have been measured as a function of Cd vapor pressure in the Cd‐Ar discharge. Except for the 2981‐A line, the intensities are highest at Cd vapor pressures in the range 5–30 mTorr. The 2981‐A line increases in intensity with increasing Cd vapor pressure in the 5–200‐mTorr range. Absolute radiant flux densities have been determined by calibrating the spectrometer response using a low‐pressure mercury discharge.

If A is a set colored with m colors, and B is colored with n colors, the coloring of A × B obtained by coloring (a, b) with the pair (color of a, color of b) will be called an m × n simple product coloring (SPC) of A × B. SPC's of Cartesian products of three or more sets are defined analogously. It is shown that there are 2 × 2, and 2 × 2 × 2 SPC's of Q2 and Q3 which forbid the distance one; that there is no 2k SPC of Qk forbidding the distance one, for k > 3; and that there is no 2 × 2 SPC of Q × Q(√15), and thus none of R2, forbidding the distance 1.

We present the first observation to our knowledge of the molecular shape resonance in adsorbed CO using the technique of inverse photoemission. By comparison with earlier photoionization measurements we are able to examine the role of the final-state potential in determining the binding energy of the shape resonance. We find that screening of the photohole is more effective for valence-band photoionization than for the more localized core-level photoionization.

Valence-band photoemission measurements have been made both above and below the ${T}_{c}$ of ${\mathrm{Ba}}_{2}$${\mathrm{YaCu}}_{3}$${\mathrm{O}}_{9\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ where \ensuremath{\delta}=2.1. We find similarities to recent calculations of the electronic properties. However, the experimental binding energies are between 1.0 and 1.4 eV further from the Fermi level than the calculation. We suggest that this difference may affect attempts to predict ${T}_{c}$ from tight-binding modeling of the electron-phonon mechanism.

An inverse-photoemission study (at $\ensuremath{\hbar}\ensuremath{\omega}=9.7$ eV) of the adsorption of carbon monoxide on a Pd(111) surface is compared with a first-principles calculation of the cross section for the emission of photons as a function of electron angle of incidence. It is found that the calculation is able to explain the experimental results in terms of the relative strengths of the $\ensuremath{\sigma}\ensuremath{\rightarrow}\ensuremath{\pi}$ and $\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\pi}$ channels in the optical transitions.

Two different models for the dependence of diffuse reflectance of powders on optical absorption coefficient, particle size, and index of refraction are discussed. For particles large compared to the wavelength of incident radiation a model in which the path of this radiation is controlled mainly by specular internal and external reflections and refraction is preferable to one in which path deviation by Lambert law scattering dominates.

Let G=(V,E) be a graph. A subset S of V is said to be secure if it can defend itself from an attack by vertices in N[S]−S. In the usual definition, each vertex in N[S]−S can attack exactly one vertex in S, and each vertex in S can defend itself or one of its neighbors in S. A defense of S is successful if each vertex has as many defenders as attackers. We look at allowing an attacking vertex to divide its one unit of attack among multiple targets, or allowing a defending vertex to divide its one unit of defense among multiple allies. Three new definitions of security are given. It turns out that two of the new definitions are the same as the original.

VUV photoemission spectra (Fig. 1) of the valence bands of the high-Tc superconductor(1) YBa2Cu3O9−δ δ=2.1, have been measured using the UV undulator (beam line U5U). Photon erergies h v = 45.0 eV and 52.0 eV lie within the first harmonic flux output from the undulator, while h v = 105.0 lies within the second harmonic. The spectra at h v = 21.2 eV and 40.8 were taken using a He resonance lamp.

We present the results of experimental and theoretical investigations of the Pd/Nb (110) interface. In the experiment we identify an interface resonance which clearly displays the required two-dimensional character of such a state. We further show that it is derived from a surface resonance present on the bare niobium. The presence of the Pd overlayer serves to localize and increase the surface character of this state rather than quenching it. The theoretical calculations support the identification of this state as an interface state and further indicate that its intensity reflects the strength of the interface bond.

Spin-split adsorbate-induced bands have been observed for $p(1\ifmmode\times\else\texttimes\fi{}1)$ oxygen and $c(2\ifmmode\times\else\texttimes\fi{}2)$ sulfur on Fe(100) by use of spin-polarized angle-resolved photoemission. For the ${p}_{z}$-symmetry orbitals, the exchange splitting is considerably larger at the Brillouin-zone center (1.3 eV for O, 0.5 eV for S) than at the zone edge (0.25 and 0.2 eV, respectively). This is attributed to enhanced hybridization with substrate $d_{z}^{}{}_{}{}^{2}$ orbitals when the adsorbate ${p}_{z}$ band overlaps the bulk continuum. Our observation of an exchange splitting provides evidence of a small magnetic moment on the adsorbate atoms. Our results also indicate that the adsorbate layer is ferromagnetically aligned with the substrate.

We show that the binding energy of surface states is a multibranch function of the image-plane position. The states of the Rydberg series (including the conventional crystal-derived states) have a unique labeling in terms of the number of extrema in the wave function beyond the crystal edge, and the spatial extent of the image states is determined by their binding energy. In addition, we find that the image plane is further from the crystal edge on more loosely packed surfaces and that dynamical corrections to the image potential account for increases in the effective mass of 5%.

Suppose I is an open real interval, and V a subspace of C∞(I) invariant under D, differentiation. It is shown that if V contains a polynomial of positive degree, then D has no homogeneous qth root on V, for any integer q > 1. This conclusion is not generally true if I is replaced by an arbitrary open set in the reals. Necessary and sufficient conditions for the existence of qth roots of D on finite dimensional subspaces of C∞(I) invariant under D, in terms of the differential equations of which such subspaces are the solution spaces, are obtained.

Inverse-photoemission spectra (IPES) recorded from Nb(110) allow the unoccupied bands to be mapped. The critical points are identified and the approximate form of the high-lying ${\ensuremath{\Sigma}}_{1}$ band established. This latter band serves as the initial state in IPES and the final state in photoemission studies. It is suggested that disagreement between theory and experiment for the ${T}_{25\mathcal{'}}$ critical point probably reflects the presence of a surface resonance. Fluorescence is also observed from the decay of the Nb 4p core holes. The relative intensity of the fluorescence due to 4${p}_{3/2}$ and 4${p}_{1/2}$ core holes is discussed in terms of possible Coster-Kronig transitions.

We report the observation of the resonant enhancement of inverse photoemission transitions involving bulk band states of niobium when the energy of the transition corresponds to the plasma frequency. On resonance the cross-section increases by a factor of \ensuremath{\sim}5. Comparison with earlier reflectivity data confirms that the resonance occurs at the plasma frequency but the mearsured plasmon energy of 19.3 eV is slightly less than the 20.8 eV found in the earlier study. We do not observe resonant enhancement of transitions into surface states or interface states.

We observe directly the radiation emitted from excited hydrogen atoms following their electron stimulated desorption from an al kali-promoted Ni(001) surface. We observe Lyman α, s, γ radiation. The line width and energy of the emitted radiation indicate that the hydrogen atoms are well removed from the metal surface at the point of deexcitation. By comparing the desorption cross-section for these states with the desorption cross-section of hydrogen ions we find that the excited hydrogen atoms are emitted directly from the surface rather than resulting from the reneutralization of desorbed ions. The intensity of Lyman α radiation is over an order of magnitude greater than the intensity of Lyman s and γ radiation suggesting either a higher probability for excitation into the hydrogen 2p state initially or a higher probability of resonance ionization of the higher excited states.

The surface magnetic properties of the rare earth Lanthanide, gadolinium (Gd) have been the subject of a number of different experimental and theoretical studies in recent years. These studies have suggested that the surface of Gd exhibits a variety of unusual magnetic properties including imperfect ferromagnetic coupling between the surface and bulk, canted magnetic moments and some form of phase transition. Also the temperature dependent behavior appears to be quite controversial with both a Stoner-like and spin-mixing behavior invoked to describe the loss of magnetization. With new angle- and spin-resolved studies carried out at room and low temperatures, we re-examine this temperature dependence and confirm that both types of behavior are evident. We further provide direct evidence that at the temperature of liquid nitrogen, it is possible to observe a canting of the surface moments out of the surface plane.

Next generation light-sources, electron coolers, high-power FELs, Compton X-ray sources and many other accelerators were made possible by the emerging technology of high-power, high-brightness electron beams. In order to get the anticipated performance level of ampere-class currents, many technological barriers are yet to be broken. BNL’s Collider-Accelerator Department is pursuing some of these technologies for its electron cooling of RHIC application, as well as a possible future electron-hadron collider. We will describe work on CW, high-current and high-brightness electron beams. This will include a description of a superconducting, laser-photocathode RF gun and an accelerator cavity capable of producing low emittance (about 1 micron rms normalized) one nano-Coulomb bunches at currents of the order of one ampere average.

We report progress on the R&D program for electron-cooling of the Relativistic Heavy Ion Collider (RHIC). This electron cooler is designed to cool 100 GeV/nucleon at storage energy using 54 MeV electrons. The electron source will be a superconducting RF photocathode gun. The accelerator will be a superconducting energy recovery linac. The frequency of the accelerator is set at 703.75 MHz. The maximum electron bunch frequency is 9.38 MHz, with bunch charge of 20 nC. The R&D program has the following components: The photoinjector and its photocathode, the superconducting linac cavity, start-to-end beam dynamics with magnetized electrons, electron cooling calculations including benchmarking experiments and development of a large superconducting solenoid. The photoinjector and linac cavity are being incorporated into an energy recovery linac aimed at demonstrating ampere class current at about 20 MeV.

The intensity of the 1942‐A Hg+ ion resonance line in Hg‐inert‐gas discharges has been measured as a function of current density and Hg pressure in the range from 1 to about 15 A/cm2 and pressure from 10−3 to 0.5 Torr. In the Hg–Ar discharge the intensity of this line varies as the 1.75 power of the current density, while in Hg–Kr, the exponent is 2.0. There is evidence for volume recombination which is inhibited when Ar is replaced by Kr.

The optical absorption spectrum of thallium-activated potassium chloride has been measured at 2000 atmospheres. The absorption band corresponding to the $^{1}S_{0}\ensuremath{\rightarrow}{^{3}P_{1}}^{0}$ transition of ${\mathrm{Tl}}^{+}$ shifts 4 A to longer wavelengths at this pressure. The spectral shift is calculated theoretically from the quantitative configuration coordinate model of KCl: Tl. The occupation probabilities of accessible atomic configurations of the activator system are dependent on pressure, whereas the transition energy for a particular configuration is independent of pressure. The pressure is considered to act hydrostatically on six pistons corresponding to the ${\mathrm{Cl}}^{\ensuremath{-}}$ nearest neighbors. The theoretical shift in absorption under 2000 atmospheres pressure is 5 A to longer wavelengths.

The optical absorption and the excitation spectrum for luminescence of synthetic periclase crystals have been determined in the vacuum ultraviolet. From these measurements it is deduced that the width of the forbidden energy band of MgO is approximately 7.4 ev.