Energy Of Incident Radiation Research Articles

Thermocapillary convection in an absorbing-scattering medium subjected to irradiation

The criteria for the onset of thermocapillary convection in a horizontal radiating fluid layer heated by an incident thermal radiative energy source are determined. The fluid layer is an absorbing and isotropically scattering medium confined between a free upper surface and an insulated rigid lower surface. Linear analysis is performed on the continuity, momentum, energy, and approximate radiative equations. The resulting disturbance equations are solved using a numerical optimization technique to obtain the eigenvalues governing the onset of convective motion. The influence of thermal radiation on the critical Marangoni number is examined. Attention is drawn to the physical significance of the heat transfer mode, gravitational force, the scattering effect, and the surface radiative properties. The conditions leading to the onset of convection are presented as functions of the optical thickness, scattering albedo, Planck number, surface emissivities, and transmissivities.

Influence of Primary and Scattered Radiation on Speed and Contrast of Screen-Film Systems and Their Perception in Test Phantoms

Speed and contrast of screen-film systems are influenced by the ratio of primary and scattered radiation. Incident angle and radiation energy, thickness, transparency, and phosphor materials have effects on the radiation transformation process. Measurements of contrast enhancement and contrast-detail diagrams are presented.

Influence of Primary and Scattered Radiation on Speed and Contrast of Screen-Film Systems and Their Perception in Test Phantoms

Speed and contrast of screen-film systems are influenced by the ratio of primary and scattered radiation. Incident angle and radiation energy, thickness, transparency, and phosphor materials have effects on the radiation transformation process. Measurements of contrast enhancement and contrast-detail diagrams are presented.

An analysis of paramagnetic centers in irradiated dentin using electron spin resonance

The ESR spectra produced in irradiated dentin have been studied over a range of incident radiation energies from 50 kVp to 25 MVp. The behavior of the dentin ESR signal strength is similar to that of enamel as a function of the energy of the incident radiation. The magnitude of the dentin ESR signals are, however, up to 10 times smaller than the signals of dental enamel for a given radiation energy. The possible contributions of radiation interaction coefficients, chemical structure, and crystallite size to the differences in ESR spectra are discussed.

Study of the influence of iron and lanthanum oxides on the band structure of Pb(Zr, Ti) O3

The measurements of diffuse reflectance spectra in the range ofλ e 〈400; 2500〉 nm and of photoacoustic spectra in the range ofλ e 〈350; 800〉 nm were used for the study of the influence of iron (III) oxide and lathanum oxide additions on the band structure of polycrystalline lead zirconate — lead titanate solid solutions. The molar ratio of zirconium and titanium in the studied solid solutions was 60 ∶ 40, and the concentrations of the dopants werex FeO1.5, andy LaO1.5, werex e 〈0; 0·05〉 mol, andy e 〈0; 0·10〉 mol, respectively. The diffuse reflectance spectra were expressed in terms of the Kubelka-Munk function values versus incident electromagnetic radiation energy. These dependences were decomposed into partial “absorption” bands using a computer. Transitions of charged carriers between energy levels or bands which differ mutually by the energy of 0·9, 1·2–1·3, 1·6, 1·65–1·7, 2·4–2·5, 2·75–2·8, 2·9–3·2, 3·4–3·8 eV, were identified. Their intensities depend on the concentration of Fe and/or on La in the Pb(Zr0.60 Ti0.40) solid solutions.

Time-dependent calculations of X-ray and gamma-ray reprocessing

view Abstract Citations (26) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Time-dependent Calculations of X-Ray and gamma Reprocessing Cominsky, Lynn R. ; London, Richard A. ; Klein, Richard I. Abstract Numerical calculations of the reprocessing of high-energy X-ray and gamma-ray radiation (from 1 keV to 1 MeV) have been performed. The incident radiation is assumed to be instantaneously deposited in a hydrostatic stellar atmosphere, changing both the temperature and ionization structure. A fully implicit numerical method is then used to solve the nonlinear diffusion equation for the transfer of the reprocessed radiation. The results of 38 numerical models are presented. Model parameters that were varied include the effective temperature and gravity of the absorbing star and the fluence and spectral temperature of the incident high-energy radiation. For each model, the time to reemit 50 and 99 percent of the incident radiation energy is tabulated. Model results are compared to the extensive observations of coincident X-ray and optical bursts and to the recent reports of correlated gamma-ray burst and optical emission. Publication: The Astrophysical Journal Pub Date: April 1987 DOI: 10.1086/165122 Bibcode: 1987ApJ...315..162C Keywords: Gamma Ray Bursts; Radiative Transfer; Stellar Atmospheres; Temporal Distribution; X Rays; Diffusion Theory; Gravitational Effects; Ionization; Stellar Temperature; Astrophysics; GAMMA RAYS: GENERAL; RADIATIVE TRANSFER; X-RAYS: BURSTS; X-RAYS: GENERAL full text sources ADS |

Optical second-harmonic generation from thallium on silver.

Light which was generated at the surface of polycrystalline Ag was monitored in the specular direction at the second-harmonic energy of the neodynium-doped yttrium aluminum garnet laser incident radiation as a function of the applied voltage in a thin-layer electrochemical cell (0.05M ${\mathrm{H}}_{2}$${\mathrm{SO}}_{4}$) with and without the presence of 0.75\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$M ${\mathrm{Tl}}^{+}$. The second-harmonic generation (SHG) decreased when ${\mathrm{Tl}}^{+}$ became physisorbed prior to underpotential deposition (UPD) of a stable Tl monolayer and increased slightly upon UPD of Tl. In contrast to this, previously reported reflectance data at the first harmonic are insensitive to events preceding Tl deposition. These results point out basic differences between SHG and reflectance of the fundamental and also show that simple surface-charge-density arguments are unsatisfactory in the explanation of SHG surface phenomena.

Subband-Landau-level spectroscopy in GaAs-AlxGa1-xAs heterojunctions.

Resonant coupling of the subband Landau levels in the two-dimensional electron gas of high-mobility GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As heterojunctions has been measured, and a detailed analysis is presented. We have investigated the subband structure and the coupling strength using cyclotron resonance at energies near the transition energy between the subband levels. This was done at constant magnetic field for a range of energies by far-infrared interferometry, and for a fixed energy of incident radiation while varying the strength of the applied magnetic field. In both cases, a broadening and splitting of the cyclotron resonance line were observed. We show that one thus directly obtains the subband transition energy and the coupling strength which depend strongly on the shape of the interface potential. Calculations of the hybridization of the subband Landau levels, based on a triangular potential well, result in an energy, field, and angle dependence of the coupling in good agreement with experimental observations and reproduce the double resonance observed at a fixed energy of laser radiation. The electron concentration was influenced either by illuminating the sample or by applying a back gate voltage on the GaAs substrate, and the resulting variation of the transition energy is found to be in accordance with the results of self-consistent calculations.

Study of a ruby laser with a passive shutter based on a LiF crystal with F 2 + color centers

A large body of current work is dedicated to the study of materials with saturable absorption suitable for passive modulation of the Q of ruby lasers. LiF crystals with F/sub 2//sup +/ color centers are proposed as a passive shutter; however, their prospects to date are unclear. The authors' goal in this paper is a more detailed study of the characteristics of a ruby laser with a passive shutter of LiF:F/sub 2//sup +/ obtained by irradiating LiF crystals with gamma radiation from a cobalt-60 source. Crystals with an OH additive were used to obtain stable LiF:F/sub 2//sup +/. The passive shutter used in the experiments was a parallelepiped 20 x 20 x 9 mm. The initial transmittance of the crystal at the 694 nm wavelength was 41%. To determine these and other parameters of a passive shutter based on these crystals, the authors based their method on measurement of the shutter transmission as a function of the amount of energy of the incident pulsed radiation. The most homogeneous central portion of the beam of the pulsed ruby laser radiation was selected using a diaphragm 5 mm in diameter and was directed to the sample under study.

Electron density and polarized absorption spectra of fayalite

The maxima of the electron difference densities of Fe2+ atM(1) andM(2) positions of fayalite, Fe2SiO4, determined by x-ray diffraction are considered to correspond to atomic dipoles. Provided the selection rules of dipole radiation are satisfied and the energy of the incident radiation lies within the appropriate range, the interaction of incident radiation with these atomic dipoles should lead to three absorption bands of which two originate from Fe2+ atM(1), one from Fe2+ atM(2). The relative intensities of the three bands, dependent on the polarization direction, are estimated. The result ist in excellent agreement with the interpretation of olivine spectra given by Burns (1970).

Spatial-temporal coherence of Stokes radiation under conditions of stimulated Brillouin scattering compression in liquids

It is demonstrated experimentally that efficient stimulated Brillouin scattering (STBS) compression of 10–20 nsec pulses to ~ 2 nsec may be achieved in liquids with a high conversion efficiency and with a close to the ultimate spatial–temporal coherence. It is established that there is a critical incident radiation energy that depends on the pump pulse duration. Above this energy abrupt spatial and temporal changes in the amplitude and phase characteristics of the Stokes radiation are observed.

One‐Phonon Resonance Raman Scattering

AbstractIndirect creation and annihilation probabilities for a Wannier‐Mott exciton with arbitrary kinetic energy and interacting with longitudinal optical (LO) phonons are obtained as a function of temperature. These results are applied to the calculation of the one‐phonon (Stokes and anti‐Stokes) resonance Raman scattering (RRS) cross‐section in the case when the intermediate states are considered to be hot excitons, interacting with the LO‐phonons. The scattering cross‐section of these processes in CdS at 77, 150, and 300 K are presented as a function of the incident radiation frequency. It is shown that the cross‐section calculated for high temperatures and for incident radiation energies larger than the energy gap is dominant with respect to the cross‐section corresponding to processes in which only one phonon participates (no indirect transition).

Laser Surgery of the Lens: Experimental Studies

The authors used high peak power nanosecond (Q-switched) and picosecond (mode-locked) pulses from the neodymium-YAG laser to perform experimental anterior and posterior capsulotomy in rabbits. The morphology of laser anterior capsulotomy was studied using scanning electron microscopy. Ultrastructural studies revealed no evidence of morphologic abnormality in the corneal endothelium in eyes in which laser capsulotomy had been performed. The critical factors for the prevention of inadvertent retinal injury during laser surgery in the anterior segment of the eye were identified as pulse energy and cone angle of incident laser radiation. Using wide angle fundus photography and fluorescein angiography, intentional retinal injury during laser surgery of the lens was experimentally documented when retinal radiant energy exposure exceeded injury threshold.

Study of the Influence of Manganese and Lanthanum Oxides on the Band Structure of Pb(Zr, Ti)O3

The measurements of diffuse reflectance spectra in the range ofλ e 〈400; 2500〉 nm and of photoacoustic spectra in the range ofλ e 〈350; 800〉 nm were used for the study of the influence of iron (III) oxide and lathanum oxide additions on the band structure of polycrystalline lead zirconate — lead titanate solid solutions. The molar ratio of zirconium and titanium in the studied solid solutions was 60 ∶ 40, and the concentrations of the dopants werex FeO1.5, andy LaO1.5, werex e 〈0; 0·05〉 mol, andy e 〈0; 0·10〉 mol, respectively. The diffuse reflectance spectra were expressed in terms of the Kubelka-Munk function values versus incident electromagnetic radiation energy. These dependences were decomposed into partial “absorption” bands using a computer. Transitions of charged carriers between energy levels or bands which differ mutually by the energy of 0·9, 1·2–1·3, 1·6, 1·65–1·7, 2·4–2·5, 2·75–2·8, 2·9–3·2, 3·4–3·8 eV, were identified. Their intensities depend on the concentration of Fe and/or on La in the Pb(Zr0.60 Ti0.40) solid solutions.

Internal photoemission in Ag-Al<inf>2</inf>O<inf>3</inf>-Al junctions

We report a detailed study of the magnitude of the photon-induced current in Ag-Al 2 O 3 -Al metal-oxide-metal junctions as a function of photon energy and angle of incident radiation. Experimental observations and a theory based on vacuum photoemission are found to be in good agreement. Fast risetimes ( \lsim50 ns) and linearity of the photocurrent with respect to incident power up to at least 10 kW/cm2are also reported.

Electronically excited nitric oxide by vacuum ultraviolet photodissociation of nitroso-compounds and nitrites

The gas-phase photolysis of CF3NO and EtONO at 123 and 147 nm and of ButNO at 147 nm gives rise to electronically excited nitric oxide which fluoresces. The strongest emission is that of the A2∑+–X2II transition (γ-bands), although other transitions are also observed. The vibrational level populations in the NO(A2∑+) state show some correlation with the energy of the incident radiation and the strength of the R–NO bond. Addition of helium to the CF3NO or EtONO produces an enhancement of emission from the v′= 2 and 3 levels of the A2∑+ state, while emission from v′= 0 and 1 is almost unchanged. Addition of low pressures of N2 and H2 also gives some enhancement of v′= 2 and 3. These observations are discussed in terms of the possible excited states of NO produced during the photolysis, and the deactivating effects of the added gas. Photolysis of ONCN at 147 nm yields electronically excited cyanide radicals and the (B2∑–X2∑) violet bands are observed. There is evidence for considerable rotational excitation of the CN radical, an effect well known in the vacuum u.v. photolysis of other cyanides, e.g. ICN.

A 4π CaF2(Eu) scintillation spectrometer for measurements with X-ray and electron sources

A 4π CaF2(Eu) scintillation spectrometer is described which is suitable for measurements with electrons and X-rays. The detection efficiency for these radiations has been measured using 32P and 109Cd sources respectively. In addition, the resolution, linearity of response and total photon efficiency have been determined for this detector as functions of incident radiation energy. An insensitive region on the surfaces of CaF2(Eu) crystals was determined to be (0.47 ± 0.10) mg/cm2 thick using a collimated 252Cf α-source. A brief study of negaton and positon continuum spectra, obtained using 32P and 120Sb sources respectively, is also described together with the corresponding Fermi-Kurie plots.

Extended x-ray-absorption fine structure—Auger process for surface structure analysis: Theoretical considerations of a proposed experiment

A method for surface structure analysis is proposed. The proposed process combines x-ray photoabsorption and Auger electron emission. The extended x-ray-absorption fine structure, occurring for photon energies above an atomic absorption edge, contains structural information of the microscopic environment due to the coupling of the photoelectron final state with the atomic initial state. Measurement of the variations in the intensity of particular Auger lines, as a function of the incident radiation energy, provides a surface sensitive measure of the photoabsorption cross section in the media. Theoretical considerations of the physical processes underlying the proposed experiment and its feasibility, and a discussion of background contributions are presented.

Variation of Erythema With Monochromator Bandwidth

<h3>To the Editor.—</h3> It is well known that the skin response to ultraviolet radiation in the sunburn range (280 to 320 nm) is dependent on the bandwidth of the incident radiation.¹The results presented here show the calculated variation of erythemal effectiveness with monochromator bandwidth for radiation beams of equal fluence, ie, the incident radiation energy per square centimeter (usually expressed as<i>mJ</i>· cm^-2) is constant. In the determination of action spectra, a monochromator with equal entrance and exit slit widths is usually used. In a perfect monochromator, this arrangement gives a triangular distribution of intensity at the exit slit, with a maximum intensity at a central wavelength<i>w</i>₀. The wavelengths present in the beam extend from<i>w</i>₀—<i>B</i>to<i>w</i>₀+<i>B</i>, where<i>B</i>is termed the bandwidth and is equal to the width of the distribution at half the maximum intensity.²

Optical absorption of glassy semiconductors of the GeSbSe system

The optical transmittance of chalcogenide glasses Ge 2SbSe 7 (I), Ge 3SbSe 6 (II), GeSb 2Se 7 (III) and GeSbSe 3 (IV) was studied in the near infrared spectral region, 0.7–25 μm. The longwavelength tail of the absorption edge can be described by Urbach's rule. At higher absorption levels the absorption coefficient K depends quadratically on the energy of incident radiation. The temperature dependence of the absorption edge is discussed and the optical gaps 1.77 eV (I), 1.67 eV (II), 1.66 eV (III), 1.57 eV (IV) together with the corresponding temperature coefficients are also determined. The studied glasses are quite transparent in the 600–5000 cm −1 wavenumber range.