Monochromatic Line Research Articles

A double-crystal monochromator for EXAFS at BSRL

The details of the double-crystal monochromator and its control system of the first monochromatic photon beam line for EXAFS studies 4W1B at Beijing Synchrotron Radiation Laboratory are described in this paper, the commissioning and the first experimental results obtained are also presented.

Radiative transfer in cylindrical plasmas

The characteristic functions determining radiation transfer in cylindrical systems by both monochromatic radiation and spectral lines are derived. Functional forms for the scattering of monochromatic and Doppler-broadened lines with complete redistribution in a uniform medium are derived, and suitable approximations for rapid calculation identified.

Optical studies of direct modulation doping and quantum wire formation by focused Si on beam implantation

The two-dimensional electron gas (2DEG) produced by a Si++ focused ion beam implantation into GaAs–AlGaAs quantum well structures grown by molecular beam epitaxy (MBE) has been studied by low temperature (15 K) cathodoluminescence (CL), photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopy. Ion channeling effects were used and the Si ion activation was optimized during the rapid thermal annealing following the implantation. PL and PLE measurements were first performed in situ the electron microscope together with the CL to evaluate the 2DEG formation in a uniformly implanted pattern. The localized 2DEG created by linear modulation doping (line dose 1.5×108 ions/cm) was imaged, and a local band bending of ∼25 meV was determined from the monochromatic CL line scanning.

Double-crystal x-ray spectroscopy at JET

A double-crystal monochromator has been brought into operation at JET to measure absolute wavelengths and intensities of impurity spectral lines in the soft x-ray region from about 0.1 to 2.3 nm. It is capable of operating also during the deuterium-tritium (active) phase of JET because its detector is very effectively shielded against neutrons and hard x rays. The spectrometer has been swept over a wide wavelength range, around characteristic line groups as well as monochromatic line scans.

Stepwise reduction of coordinated dinitrogen to ammonia via diazinido and hydrazido intermediates on a visible light irradiated Pt/CdS · Ag 2S/RuO 2 particulate system suspended in an aqueous solution of K[Ru(EDTA-H)Cl]2H 2O

We report the photocatalytic fixation of coordinated dinitrogen to ammonia in aqueous solution under ambient conditions (30 °C and 1 atm N 2) in the presence of the modified semiconductor particulate system Pt/CdS · Ag 2S/RuO 2 catalysed by K[Ru(EDTA-H)Cl]2H 2O. Doping of the photon absorber CdS with Ag 2S (0.05 wt.% relative to the weight of CdS) leads to an enhanced rate of production of NH 3 at 505 nm. The reaction shows a first-order dependence on the catalyst concentration. The quantum yields of the product were obtained at five monochromatic absorption lines between 450 and 550 nm. Illumination of the system with 505–525 nm light gives the highest quantum yield of 0.35. A mechanism is proposed for the formation of NH 3 which involves the in situ formation of a dinitrogen complex of ruthenium(II). The —NN bond in this complex appears to undergo stepwise reduction to NH 3 via diazinido and hydrazido intermediates which were characterized by the nuclear magnetic resonance (NMR) spectra of the solution from the reaction cell. The estimated deuterium kinetic isotope effect is 1.77 indicating a hydrogen atom transfer in the rate-determining step. The source of the nitrogen atom in NH 3 is dinitrogen as confirmed by 15N 2 studies. Photo-oxidation of H 2O to oxygen is confirmed by performing studies in H 2 18O (10%) enriched medium.

Control of beam intensity signal and position at NSLS X9

X-ray beam line fluctuation is a common problem at almost all synchrotron beam lines. The vertical and horizontal fluctuations are time dependent and vary in amplitude and frequency at each synchrotron. In many cases the amplitudes of the fluctuations are higher than required by users (± 100 μm at the National Synchrotron Light Source). For time resolved X-ray absorption spectroscopy these kinds of amplitudes at noise frequencies are certainly out of proportion to the useful needs of synchrotrons. We have made an attempt to compensate for this noise at the experimental end of the beam line. It has been reduced to ±15 μm on monochromatic beam line X9A and white X-ray beam line X9B. Compensation is basically for low frequencies (< 1 Hz) and for the slow drifts of the X-ray beam during a fill.

Expected Scientific Performance of the Three Spectrometers on the Extreme Ultraviolet Explorer

AbstractThe expected in-orbit performance of the three spectrometers included on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite is presented. Recent calibrations of the gratings, mirrors and detectors using monochromatic and continuum EUV light sources allow the calculation of the spectral resolution and throughput of the instrument. An effective area range of 0.2 to 2.8 cm2 is achieved over the wavelength range 70-600Å with a peak spectral resolution λ/Δλ (FWHM) of ~ 360 assuming a spacecraft pointing knowledge of 10 arc seconds (FWHM). For a 40,000 sec observation, the average 3σ sensitivity to a monochromatic line source is 3 × 103 photons cm-2 sec-1. Simulated observations of known classes of EUV sources such as hot white dwarfs and cataclysmic variables are also presented.

Replaceable Be and Al windows for X-ray beam lines

Construction details and results of on-going performance tests are presented for two ultrahigh vacuum compatible, free-convection cooled window assemblies in which the window disk is easily replaceable. In the Be window assembly, an 0.25 mm thick Be disk, 38 mm in diameter, is sealed into a stainless steel adapter flange using 0.5 mm diameter pure Al wire. The assembly is leak tight to better than 1 × 10 −10 atm cm 3/s before and after multiple bakeouts to 250°C. However, an unexplained temperature-dependent He leak, with a maximum magnitude in the low 10 −10 atm cm 3/s range at 250°C, appears during bakeout. Possible causes for this leak are discussed. In the Al window assembly, a 25 μm thick Al disc, 60 mm in diameter, acts as the sealing medium as well as the window material over a 10 mm × 50 mm opening. This assembly remains leak tight to better than 1 × 10 −10 atm cm 3/s throughout multiple bakeouts to 150°C and has been successfully tested in white and monochromatic beam lines at the NSLS X-ray ring.

Improved Lyman-alpha hygrometer for small-scale atmospheric turbulence measurements. Part II: The O2 filtering technique

The detector of the IMST/SA-CNRS improved Lyman-alpha hygrometer is a solar-blind photomultiplier tube that ensures large signal-to-noise ratio and allows a miniaturization of the sampling volume. This PM tube has a relatively large spectral response and can detect, in addition to the Lyman-alpha line, hydrogen molecular transitions emitted by the discharge source between 120 and 180 nm. In order to avoid a spurious sensitivity to oxygen density fluctuations, an active filtering cell is added to absorb the undesired lines. The instrument sensitivity is calculated with the help of a two-gas, three-spectral-line UV-beam absorption model, fitted to calibration measurements. The technique of the active filtering associated with the three-line absorption model produces the following advantages: (1) reduced sensitivity to oxygen fluctuations, (2) a clear physical meaning to the model terms allowing the sensitivity computation in most conditions, (3) increased signal-to-noise ratio, and (4) in most conditions, improved sensitivity to water vapor compared to the monochromatic Lyman-alpha line.

A gamma-ray constraint on the nature of dark matter

If even a small component of the Galactic spheroid consists of the weakly interacting majorana fermions that are cold-dark-matter candidate particles for the Galactic halo, there should be a substantial flux of annihilation gamma rays from a source of about 1-deg extent at the Galactic center. COS B observations already constrain the halo cold-dark-matter (CDM) content entrained in the inner spheroid to be less than about 10 percent. A somewhat weaker constraint applies to the CDM believed to be present in the Galactic disk, but still only about 15 percent can be in such particles. Monochromatic line photons of energy 3-10 GeV are also predicted, and future experiments may be capable of improving these limits. Since both theoretical models of galaxy formation in a CDM-dominated universe and mass models for the rotation curve in the inner Galaxy suggest that a substantial fraction of the spheroid component should be nonluminous and incorporate entrained halo CDM, the hypothesis that the halo CDM consists predominantly of weakly interacting fermions such as photinos or heavy majorana mass neutrinos or higgsinos may already be subject to observational test.

Chi b states in exclusive radiative decay of the Upsilon (2S).

The Crystal Ball detector at the DESY storage ring DORIS II has been used to study radiative decays of the \ensuremath{\Upsilon}(2S) resonance. We report on the analysis of the exclusive channel \ensuremath{\Upsilon}(2S)\ensuremath{\rightarrow}\ensuremath{\gamma}${\ensuremath{\chi}}_{b}$, ${\ensuremath{\chi}}_{b}$\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\Upsilon}(1S)\ensuremath{\rightarrow}${e}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ or ${\ensuremath{\mu}}^{+}$${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$. We detect two ${\ensuremath{\chi}}_{b}$ states by observing two monochromatic photon lines at energies (107.0\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\pm\else\textpm\fi{}1.3) MeV and (131.7\ifmmode\pm\else\textpm\fi{}0.9\ifmmode\pm\else\textpm\fi{}1.3) MeV, respectively. The product branching ratios B[\ensuremath{\Upsilon}(2S)\ensuremath{\rightarrow}\ensuremath{\gamma}${\ensuremath{\chi}}_{b}$]\ifmmode\times\else\texttimes\fi{}B[${\ensuremath{\chi}}_{b}$\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\Upsilon}(1S) ] are (1.6\ifmmode\pm\else\textpm\fi{}0.3\ifmmode\pm\else\textpm\fi{}0.2)% for the first state and (2.1\ifmmode\pm\else\textpm\fi{}0.3\ifmmode\pm\else\textpm\fi{}0.3)% for the second. For the product branching ratio of the third ${\ensuremath{\chi}}_{b}$ state, which has been observed in inclusive measurements, we find an upper limit of 0.2% (90% C.L.). Combining our results with inclusive measurements, branching ratios for ${\ensuremath{\chi}}_{b}$\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\Upsilon}(1S) are derived. Using theoretical estimates for the radiative widths of the ${\ensuremath{\chi}}_{b}$ states, we determine their hadronic widths; the results are compared with QCD predictions.

Pendellösung radiation and coherent Bremsstrahlung

The spontaneous emission process, which is kinematically forbidden in vacuum, may occur for kilovolt electrons traversing thin crystals as a direct result of the dynamical diffraction process which Paul Ewald was amongst the first to understand. The history of this effect is briefly reviewed. New experimental results, and the relevant theoretical background, are given for the resulting monochromatic X-ray emission lines known as coherent Bremsstrahlung and channelling radiation. The fine structure of these lines in particular is discussed, and their effects on electron energy-loss spectra described.

Monochromatic affine lines in finite vector spaces

Let d( k, q) be the smallest positive integer d such that if the d-dimensional vector space over the q-element field is k-colored, there exists a monochromatic affine line. It is shown that d(2, 4) = 3 and d(3, 3) = 4.

Search for narrow states coupling to τ pairs in radiative ϒ decays

We have investigated the ϒ→γττ using tagged ϒ mesons from the decay ϒ'→π +π −ϒ. The photon spectrum exhibits no monochromatic line corresponding to a narrow object decaying into a τ pair and is fully compatible with the expected background contributions. The branching ratio Br(ϒ→τ +τ − is determined to be (3.07±0.46±0.22)%.

The naval research laboratory materials analysis beam line at the national synchrotron light source

The optical and mechanical designs of a monochromatic beam line being built by the Naval Research Laboratory on the X-ray ring at the National Synchrotron Light Source (NSLS) are described. The line contains a dynamically bent collimating first mirror, a fixed-exit two-crystal monochromator designed and built at the National Bureau of Standards (NBS), and a bent cylindrical mirror to focus radiation to a spot about 1.1 × 1.7 mm 2 in the 5–10 keV range. A throughput of approximately 3×10 9 photons/s. mA is expected with a E ΔE of approximately 5×10 3 with silicon crystals. The hutch will contain a six-circle diffractometer since crystallography and other X-ray scattering measurements will constitute the primary uses of the line. EXAFS and detector calibration experiments are also planned.

Measurements of stratospheric ethane in the Jovian South Polar Region from infrared heterodyne spectroscopy of the nu9 band near 12 microns

Ethane emission-line profiles from the South Polar Region of Jupiter were measured at sub-Doppler resolving powers (..nu../..delta nu..roughly-equal10/sup 6/) using the Goddard Space Flight Center infrared heterodyne spectrometer. Lines in the /sup R/Q/sub 3/-branch of the ..nu../sub 9/ fundamental of ethane near the P42 /sup 14/C/sup 16/O/sub 2/ laser transition at 829.9273 cm/sup -1/ were observed. Comparison with diode laser laboratory spectroscopy showed that the planetary line widths were limited by velocity broadening (approx.200 MHz) due to Jovian rotation within our field of view (FWHM = 2''). Peak brightness temperatures of the lines were measured to be approx.160 K implying monochromatic (unbroadened) line brightnesses approaching 170 K. Analytical fits to our data were made by direct modeling of the radiative transfer equation using a Voyager 2 polar temperature profile and various vertical profiles for C/sub 2/H/sub 6/, H/sub 2/, and NH/sub 3/. The best fit required a constant C/sub 2/H/sub 6/:H/sub 2/ mixing ratio above the 100 mbar level of 1.2 x 10/sup -6/. These results are compared with previous work and Voyager infrared interferometer spectrometer results.

Effect of self absorption on emitted intensity of Na-5890 å line in water gas combustion plasma

Numerical calculations have been carried out to explain the effect of self absorption on the nature of the emitted intensity of the Na-5890 A line of the sodium doublet in water gas combustion plasma. The self absorption is purely an effect caused by the presence of cold wall boundary layers in an MHD duct. The effect of seed concentration, core temperature, wall temperature, boundary layer thickness and profile parameter on line shapes has been studied. It has been found that seed percentage is the major factor influencing the line shape parameters and core temperature is the major factor affecting the maximum radiated monochromatic line intensity.

Geometrical aberrations in curved bragg crystal spectrometers

Under some simplifying assumptions, the line profile of a reflection of a monochromatic line observed with a curved crystal spectrometer for an extended source and curved crystal geometry is derived. In particular, the effect of the finite dimensions of source and crystal is discussed for Johann and Johansson spectrometers. Analytical and numerical studies are provided. It is shown that some parameters produce line asymmetries and shifts of the reflected line's center of gravity. For single non-zero dimensions, analytical dependences for the shifts of the line's center of gravity are derived. From numerical calculations the change of the reflected amplitude and the peak width are obtained.

Surface acoustic waves of finite amplitude excited by a monochromatic line source

A technique for obtaining a uniformly valid solution to the problem of nonlinear propagation of surface acoustic waves excited by a monochromatic line source is presented. The method of solution is an extension of the method of strained coordinates wherein both the dependent and independent variables are expanded in perturbation series. A special transformation is proposed for the independent variables so as to make the expansions uniformly valid and also to satisfy all the boundary conditions. This perturbation procedure, carried out to the second order, yields a solution containing a second harmonic surface wave whose amplitude and phase exhibit an oscillatory variation along the direction of propagation. In addition, the solution also contains a second harmonic bulk wave of constant amplitude but varying phase propagating into the medium.

Relative Efficiency of High- and Low-pressure Sodium and Incandescent Filament Lamps Used to Supplement Natural Winter Light in Greenhouses1

Abstract The relative efficiencies of high-pressure (HPS) and low-pressure sodium (LPS) lamps for plant growth were determined for 32 species of foliage and flowering plants in greenhouse under winter conditions at 37°N latitude. HPS with a relatively wide spectral emission peaking at 589 nm, and low-pressure sodium (LPS) with a monochromatic line at 589 nm were compared at 42 W/m2 irradiance in the 400–700 nm region for various lengths of time at various times of day. Although radiation in the far-red region (700–800 nm) differed, HPS and LPS equally accelerated rates of increase in fresh weights, and heights, and flowering of most herbaceous and tropical foliage plants evaluated. High-pressure sodium and LPS were ineffective, however, in promoting growth of deciduous trees and some woody plants and had no more effect than exposure of the plants to natural winter days with 0.9 W/m2 from incandescent lamps for 8 hrs (2000-0400) night interruption (long day controls). After 16 hours, about half the species showed photomorphogical differences between plants grown at intensities of 21 and plants grown at 42 W/m2 from LPS. All showed significantly better growth characteristics (fresh weight, height, early flowering) than the long day controls. Lighting during the day or night (42 W/m2 from 0800–1600 or from 2000–0400) was equally effective in promoting growth responses with 15 of the 32 species evaluated. Night lighting was more effective than day lighting with 10 of the 32 species tested. The majority of the species grew equally well when lighted 16 hours daily (0800-2400) with 21 W/m2 or 8 hours daily (2000–0400) with 42 W/m2. Effectiveness of the lighting was generally unrelated to the photoperiodic requirements of the plants. Many of the plants, which were previously classified as day-neutral (DN), flowered as if they were long day plants. Such day-neutral plants apparently required adequate light (intensity and duration) for photosynthesis. Increased daylength alone, without regard to intensity, was not sufficient to accelerate growth and early flowering of day-neutral plants. Since HPS and LPS were equally effective on most species tested, we concluded that light quality was less important than total irradiation (energy) for the growth and early flowering of many herbaceous plants.