X-ray Emission Measurements Research Articles

Binary phase zone-plate arrays for laser-beam spatial-intensity distribution conversion

We report on the theory and development of a diffractive element composed of a binary phase zone-plate array. This component conditions the intensity distribution in the focal plane of a conventional refractive lens to generate efficiently (82%) a flattop intensity envelope on target. Analysis of the design indicates that manufacturing tolerances are not critical. Experimental performances on target from x-ray emission and shock-breakout measurements are also presented.

Electronic structure and optical properties of alpha and beta phases of silicon nitride, silicon oxynitride, and with comparison to silicon dioxide.

The electronic structure and the optical properties of \ensuremath{\alpha}-${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$, \ensuremath{\beta}-${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$, and ${\mathrm{Si}}_{2}$${\mathrm{N}}_{2}$O crystals are studied by means of first-principles local-density calculations. Together with the earlier published result on \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$, a comparative study of the electronic bonding and optical excitations in these crystals becomes possible. It is found that the electronic structure of the \ensuremath{\beta} and the \ensuremath{\alpha} phases of ${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$ are similar, but with some subtle differences that can be traced to different stacking sequences of the atomic layers and the slightly different local bonding structure. The electronic structure of the ${\mathrm{Si}}_{2}$${\mathrm{N}}_{2}$O crystal cannot be adequately described as a simple superposition of ${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$ and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$. The presence of both Si-N and Si-O bonds in ${\mathrm{Si}}_{2}$${\mathrm{N}}_{2}$O crystals affects the local potential and results in a downward shift of the O levels. The calculated density of states (DOS) and the orbital-resolved partial DOS are in good general agreement with the photoemission and x-ray emission measurements. Better resolution in the calculated DOS shows that the upper valence band has five peaks rather than three.Effective charge calculation suggests the ionic formulas of the four crystals to be \ensuremath{\alpha}-(${\mathrm{Si}}^{+2.52}$${)}_{3}$(${\mathrm{N}}^{\mathrm{\ensuremath{-}}1.89}$${)}_{4}$, \ensuremath{\beta}-(${\mathrm{Si}}^{+2.50}$${)}_{3}$(${\mathrm{N}}^{\mathrm{\ensuremath{-}}1.87}$${)}_{4}$, \ensuremath{\alpha}-(${\mathrm{Si}}^{+2.60}$)(${\mathrm{O}}^{\mathrm{\ensuremath{-}}1.30}$${)}_{2}$, and (${\mathrm{Si}}^{+2.54}$${)}_{2}$(${\mathrm{N}}^{\mathrm{\ensuremath{-}}1.90}$${)}_{2}$(${\mathrm{O}}^{\mathrm{\ensuremath{-}}1.25}$). The calculated optical properties of the four crystals show similar features in the gross absorption spectra but with differences in the peak positions. It is shown that all four crystals have intrinsic absorption tails, and those of ${\mathrm{Si}}_{2}$${\mathrm{N}}_{2}$O and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$ are larger than those of \ensuremath{\alpha}-${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$ and \ensuremath{\beta}-${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$. This is explained by the nature of the wave function at the conduction-band minimum. The difference in the intrinsic band gap and the extrapolated optical gap is pointed out. Comparison with experimental data on amorphous ${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$ shows good agreement with the optical conductivity of the crystalline phases. It is also shown that ${\mathrm{Si}}_{2}$${\mathrm{N}}_{2}$O and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$ crystals have negligible optical anisotropy, while for \ensuremath{\alpha}-${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$ and \ensuremath{\beta}-${\mathrm{Si}}_{3}$${\mathrm{N}}_{4}$ the in-plane component of the dielectric function in the long-wavelength limit is smaller than the corresponding component parallel to the c axis. The calculated refractive indices are in good agreement with the limited data available.

Hg 1− xCd xTe: electrical and structural changes induced by rapid thermal annealing

The combined electrical and structural characterization of encapsulated HgCdTe annealed in a rapid thermal processor under different temperatures and times is presented. Hall effect measurements are used for the determination of the changes in carrier concentration and mobility produced during the annealing, while structural changes due to the thermal treatment are deduced from channelled proton-induced X-ray emission measurements. The results indicate that both the carrier concentration and mobility change homogeneously throughout the crystal, reaching equilibrium values that are only a function of the annealing temperature. The evolution towards equilibrium of each parameter can be fitted to exponential laws, the time constants being a function of the annealing temperature. However, the time required to reach the equilibrium mobility is always longer (by about ×3.5) than that needed to saturate the carrier concentration, for the same temperature. The crystallinity of the samples also shows a dependence on the annealing temperature. These changes are explained on the basis of generation and annihilation of mercury vacancies through the interaction with tellurium precipitates.

Optical ionization and heating of gases by intense picosecond KrF laser radiation

We report on multiphoton ionization experiments using picosecond (ps) and sub-ps UV-laser radiation at focused intensities up to 1018 W/cm2. The experiments are concerned with determining the electron temperature of optically ionized gases produced by intense KrF lasers. Thomson scattering, stimulated Raman scattering (SRS), and X-ray emission measurements have been made and compared with modeling calculations of heating. A particular objective is to identify the respective roles of above-threshold ionization, nonlinear inverse bremsstrahlung absorption, and SRS in determining the temperature of the electrons. Results for 350-fs pulses are compared with previous measurements for 12-ps pulses (for which strikingly different behavior is observed). The importance of using subps, short-wavelength lasers to minimize electron temperature is confirmed.

Absolute coverage measurements on sulphur-passivated GaAs(100)

Particle-induced X-ray emission measurements combined with Rutherford backscattering spectrometry (including channeling) have been used to measure directly the total sulphur coverage for the S-passivated GaAs(100) surface. The ion-induced X-ray measurements show that 1.1 ML (1 ML = 6.26 × 1014 cm−2) of S is found on GaAs(100) after passivation with (NH4)2S, while only 0.55 ML of S is present on the H2Sx-treated GaAs(100) surface. A clearer picture of the S-covered GaAs(100) surface emerges from a consideration of these data in conjunction with current models encompassing surface dimers.

Electronic structure of La 2−xSr xNiO 4+δ studied by soft X-ray absorption and emission spectroscopies

The OK x-ray absorption and emission measurements were performed on La 2−xSr xNiO 4+δ with different δ and x. For doped compounds, a prepeak is observed near the O 1s edge associated with doping-induced unoccupied O 2p states. The OK x-ray emission spectra of La 2−xSr xNiO 4+δ exhibit changes in their profile with variation of the excitation energy through the O 1s edge which are due to the difference in the absorption cross section for inequivalent O sites and in the degree of the localization of unoccupied states. Analysis of the results obtained suggests that for the δ>0 sample the states in the O 1s prepeak are rather localized by trapping the induced holes in small anti-Jahn-Teller polaron while for the highly Sr-doped compounds these states have itinerant character and belong to mainly in-NiO 2-plane oxygen.

Comparison of mm-wave and X-ray diagnostics of flare plasma

To compare mm-wave and X-ray diagnostics of solar flare plasma, five flares observed in 1980–1991 in Metsahovi at 22 and 37 GHz and with GOES, SMM, and GRO are studied. The first impulsive peak of the mm-wave bursts under investigation coincides in time with hard X-ray emission. The second gradual component in mm-wave emission coincides with the maximum of the soft X-ray emission measure. The bremsstrahlung mm-wave radiation from hot chromospheric plasma and gyrosynchrotron radiation driven by common population of superthermal electrons are calculated. It is shown that for mm-wave events with the first peak intensity ≤ 100 s.f.u., the thermal bremsstrahlung is more important than the gyrosynchrotron emission. The total energy of fast electrons deduced from the first peak of mm-wave bursts is one to two orders of magnitude less than that determined from the hard X-ray emission in the approximation of a thick-target nonthermal model. That can testify in favour of the hybrid thermal/nonthermal model proposed by Holman and Benka (1992). The emission measure and the energy of evaporated plasma using both mm-wave and soft X-ray data are also determined. For events investigated here the energy of evaporated chromospheric plasma is larger than the total energy of fast electron beams. We have concluded that, for evaporation, additional energy release in the chromosphere is needed. The possibility of such energy release in the framework of an advanced circuit model for solar flares is discussed.

Investigation of energy transfer in plane laser-irradiated targets with high X-ray conversion efficiency

Results of experimental and computational investigations devoted to energy transfer mechanisms and X-ray conversion efficiency in laser-produced plasma are presented and discussed. The layers of different thicknesses and diameters deposited on the plane mylar substrate were irradiated by the focused beam of Nd:glass laser. Spectrally, temporally, and spatially resolved measurements of soft X-ray emission have been carried out at power densities of 1013-1014 W/cm2. The conditions of “re-emission” zone formation have been established. Radiative heat conductivity is shown to be the important energy transfer mechanism in the experimental conditions under investigation.

Generation of nanosecond soft X-ray pulses as a result of interaction of the Nd: glass laser radiation with gas puff targets

A new method of generation of nanosecond soft X-ray pulses with a photon energy around 1 keV is presented. X-rays are generated in a high-temperature plasma, which is created as a result of the interaction of Nd:glass laser radiation with a gas puff target. The target was obtained by puffing a small amount of gas through the nozzle into the vacuum chamber by means of a pressure electromagnetic valve. The pulses of laser radiation, with pulse duration of 1 ns and energy up to 15 J, generated in the system of a high-power Nd:glass laser were used for the target heating. Spatial, spectral, and temporal measurements of X-ray emission have shown that the high-intensity soft X rays are generated as a result of the interaction of nanosecond pulses of Nd:glass laser radiation with the gas puff target. A high efficiency of X-ray generation is suggested to be related to the effect of condensation of the gas outflowing from the valve nozzle and, in effect, to the interaction of laser radiation with matter in a form of aerosol.

Measurement of Anisotropic Soft X-Ray Emission during Radio-Frequency Current Drive in the JFT-2M Tokamak

A new vertical soft X-ray pulse height analyzer (PHA) system and a tangential PHA system were used to measure the anisotropy of soft X-ray emission during lower-hybrid current drive (LHCD) and also during current drive by the combination of LHCD and electron cyclotron resonance heating (ECRH) in the JFT-2M tokamak. The strong soft X-ray emission was measured in the parallel forward direction during LHCD. When ECRH was applied during LHCD, the perpendicular emission was enhanced. The high-energy electron velocity distribution was evaluated by comparing the measured and calculated X-ray spectra. The distribution form was consistent with the theoretical prediction based on the electron Landau damping of lower-hybrid waves and the electron cyclotron damping of electron cyclotron waves for reasonable energy ranges.

Random-phase plate effects on burn-through measurements of laser-irradiated plane-layered targets

The application of random-phase plates in laser beams to improve the uniformity of target ablation is investigated by combining the simultaneous X-ray and particle emission measurements of ablation characteristics. It is shown that if some hot spots with dimensions of a few µm exist on target they persist at least during the initial stages of the laser interaction process, producing a local maximum in the ablation pressure. Lateral energy transport, inferred from the neutral particle measurements, has little influence on absorbed energy redistribution (only 1% of the energy is transported from the laser focal spot to an outer region of 2 mm size).

X-ray absorption, emission, and resonant inelastic scattering in solids.

The process of x-ray absorption and emission in solids is considered as an x-ray resonant inelastic scattering process. This coherent inelastic scattering picture has recently been used to interpret the excitation energy dependence in the x-ray emission spectra excited with synchrotron radiation. It also suggests that with near threshold excitation, the x-ray emission spectra should be spatially anisotropic. We consider the validity and implication of this approach and factors affecting the spatial and temporal coherence in the scattering process. Taking into account the relaxation effects such as the electron-electron and the electron-phonon interactions, a significant fraction of the total emission intensity may be attributed to the coherent scattering. This picture of the x-ray absorption and emission process opens up the possibility for momentum-resolved x-ray absorption and emission measurements that can be used for band-structure determination. In addition, it has important implications on the fluorescence yield method of obtaining the absorption spectra.

External-beam PIXE analysis of ancient chinese coins

The external-beam PIXE (proton induced X-ray emission) method has been applied for the determination of the elemental composition of ancient Chinese coins in the Ching Dynasty (AD 1644–1911). The X-ray emission measurements for the samples bombarded with 3 MeV protons from 9SDH-2 Pelletron tandem accelerator were carried out with the use of a 30 mm2 × 5 mm Ge(Li) detector. The external-beam milliprobe designed for the experiment is essentially the same as the one used in our previous works. Variations of composition for more than 23 samples covering a time period of about three hundred years were examined. Results on the contents of principal component elements (Cu, Zn, Pb, Sn, Sb, Fe, Ni and As) are presented and discussed.

X-ray emission from near-main-sequence B stars

view Abstract Citations (133) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-Ray Emission from Near--Main-Sequence B Stars Cassinelli, J. P. ; Cohen, D. H. ; Macfarlane, J. J. ; Sanders, W. T. ; Welsh, B. Y. Abstract Results of a Roentgen Satellite (ROSAT) X-ray survey of 12 nearby near-main-sequence B stars are presented. Objects with very low interstellar hydrogen column density were chosen to study the soft X-ray emission properties of the stars. All of the stars were detected at the 3 sigma level. Spectral fits to seven of the stars are presented, and temperatures and source emission measures are derived. The spectra and characterized by emission from gas at a temperature of about 2 x 106 K, which is lower than that typically observed for O stars. The ratio Lx/LBol decreases sharply with spectral types later than B1, reaching values of about 10-9 at B3 V; much less than the value of 10-7 that holds for O stars and early-B stars. The survey includes four beta Cephei stars and two Be stars. Our observations are consistent with the finding that beta Cephei variables have softer spectra than other stars of the same spectral type. The X-ray emission measures for the stars are compared with upper and lower limits derived using mass loss rates and terminal velocities from line-driven wind theory. It is concluded that if shocks embedded in the winds are the source of the X-ray emission then a significant fraction of the winds in B stars must be hot. One to a few shocks can account for the observed emission measures. As a function of spectral type, there appears to be a transition in X-ray emission properties at about B1 to B1.5, with later type stars having a smaller Lx/LBol ratio. Coronal and shock models are discussed in regards to the BO V star tau Sco which has an anomalously high source temperature. Publication: The Astrophysical Journal Pub Date: February 1994 DOI: 10.1086/173683 Bibcode: 1994ApJ...421..705C Keywords: B Stars; Cepheid Variables; Emission Spectra; Main Sequence Stars; Stellar Mass; X Ray Astronomy; X Ray Spectra; Astronomical Spectroscopy; Hydrogen; Interstellar Gas; O Stars; Rosat Mission; Shock Waves; Spaceborne Astronomy; Astronomy; SHOCK WAVES; STARS: EARLY-TYPE; STARS: MASS LOSS; X-RAYS: STARS full text sources ADS | data products SIMBAD (12)

PIXE ANALYSIS OF ANCIENT EARTHENWARE (MIDDLE JOMON PERIOD) EXCAVATED AT TERAMAE SITE IN FUKUSHIMA PREFECTURE

Particle induced x-ray emission (PIXE) measurements were applied to analyze constituent elements in ancient earthenware (middle Jomon period) excavated at Teramae site in Fukushima prefecture. Quantitative analyses of the earthenware and clay obtained near the site show difference in contents of the constituent elements between them.

Absolute measurements of the soft X-ray emission from vacuum spark discharges

Low-inductance vacuum spark discharges display the occurence of hot tiny micropinches, which consist of anode material and which are intense emitters of X-ray radiation. This report presents absolute measurements of the brightness and energy emitted in the wavelength interval 7-14 AA and in the water window 24-27 AA. Elements were Mg, Al, Ti and Cu. The energy in the resonance line of He-like Mg can reach 100 mJ.

Electronic structure and chemical bonding in TiCoH hydrides

The experimentally obtained spectra of the K- and L-series for hydrides TiCoH 0.88 , TiCoH 1.42 of intermetallic TiCo compound and also pure Ti and Co are presented and discussed. The band structure calculations for the Ti-Co-H x system by the cluster X α -scattered-wave (SW) method were carried out. The comparison between local densities for both cluster types with tetrahedral and octahedral interstices for hydrogen occupation and measured X-ray emission spectra has led us to the conclusion that in the Ti-Co-H x unit cell, tetrahedral localization for hydrogen atoms is preferred.

The relationship between energetic electrons interacting at the sun and escaping to the interplanetary medium

The observations of energetic non-relativistic electrons interacting at the Sun and escaping to the interplanetary medium are reviewed. For large solar energetic particle events (LSEPs), the energy spectra of escaping ⪆20 keV electrons is observed to be a double power-law with a break near ∼ 100 keV. Since the bremsstrahlung cross section is well known, accurate measurement of the hard X-ray emission, such as those obtained with high resolution (∼1 keV kwhm) germanium spectrometer, can be deconvolved to obtain detailed energy distribution of the parent electrons. Such analyses indicate that the electrons interacting at the Sun in large flares may also have similar double power-law energy spectrum with a break ∼10 2 keV. At lower energies, almost all escaping electron events have energy spectra that extend in a power-law down to ∼2 keV, although the range of a few keV energy electrons against Coulomb collisions is much less than the path through the corona. Most escaping electron events are only observed at 2–20 keV energies with no associated chromospheric Hα phenomena. Thus, significant electron acceleration must occur in the high corona. Direct comparison of escaping electrons and electrons interacting at the Sun for the same flare over the energy range from ⪅ 5 keV to ∼ 100 keV suggests that electron acceleration occurs over a wide range of altitudes with the low-energy, few keV to ∼10 keV electrons escaping from the high corona and ⪆20 keV electrons escaping from the whole range of altitudes. Observation of large, over-the-limb flares show hard X-ray emission extending down to ⪅5 keV in a smooth power-law. The emission appears to come from the unocculted high corona, tens to hundreds of thousands of km above the photosphere. The large flares are also observed to produce emission of electrons into the interplanetary medium for many days. Thus, both X-ray and escaping electron observations show that the high corona is an important and dynamic source of electron acceleration.

Determination of composition, thickness and growth rate profiles of MOCVD grown Hg-xCdxTe

Rutherford backscattering spectrometry (RBS) and particle induced X-ray emission (PIXE) measurements have been performed on epitaxial Hg1-xCdxTe (MCT) layers on sapphire to determine composition, thickness and growth rates at discrete points along, and perpendicular to, the direction of gas flow in the MOCVD reactor cell. Continuous profiles of each property, over an area of 40×90 mm, have then been calculated by polynomial fitting and scaling of these discrete points. These profiles were used to compare MOCVD growth of MCT onto substrates placed on and below the cracking susceptor in the reactor cell.

Evidence for internal dielectronic excitation of slow highly charged uranium ions.

We have measured x-ray emission from the neutralization of slow ${\mathrm{U}}^{\mathit{q}+}$ ions with charge states q=61--73 and energies of 7\ifmmode\times\else\texttimes\fi{}q keV on a Be foil. We were able to resolve M-satellite groups and found an expected increase in M x-ray intensity with increasing number of M-shell vacancies in the incident ions. However, for charge states with no M-shell vacancies, we also observed a significant intensity of M x rays. We take this observation as evidence of an internal dielectronic excitation process occurring during the neutralization of the ions.