S. N. Andreev

Radiative heating of thin Al foils by intense extreme ultraviolet radiation

The effect of induced transparency of thin Al foils radiatively heated by intense extreme ultraviolet (EVU) radiation has been observed. The radiation of the plasma of Z-pinches appearing under the compression of tungsten liners at the Angara-5-1 facility has been used as the radiation that heats the Al foil (peak illumination on the foil ~0.55 TW/cm2) and is transmitted through it. The photoabsorption has been studied in the formed aluminum plasma at temperatures of ~10–30 eV in the density range of ~1–20 mg/cm3 in the wavelength range of ~5–24 nm. Absorption lines of Al4+...7+ ions have been identified in the experimental spectrum. In addition, radiative gas-dynamic simulations of the foil heating and expansion have been performed taking into account radiation transfer processes.

Ionization of heavy ions in collisions with neutral atoms at relativistic energies

Ionization processes of heavy ions colliding with atoms and ions at relativistic energies are considered. Formulaes for calculating ionization cross sections in the Born approximation using momentum-transfer representation without regard to magnetic interactions are given as well as those in dipole and impulse approximations. Using the LOSS-R [25] and HERION codes, calculations of relativistic cross sections are performed for H-like multiply changed ions with the nuclear charge Z ≈ 80−90, colliding with neutral atoms and for multiply changed uranium ions colliding with protons and carbon atoms. The results of calculations are compared with available experimental data and calculations performed by other authors.

Influence of relativistic effects on electron-loss cross sections of heavy and superheavy ions colliding with neutral atoms

The influence of relativistic effects, such as relativistic interaction and relativistic wave functions, on the electron-loss cross sections of heavy and superheavy atoms and ions (atomic number Z ≳ 92) colliding with neutral atoms is investigated using a newly created RICODE-M computer program. It is found that the use of relativistic wave functions changes the electron-loss cross section values by about 20–30% around the cross-section maximum compared to those calculated with nonrelativistic wave functions. At relativistic energies E ≥ 200 MeV/u, the relativistic interaction between colliding particles leads to a quasiconstant behavior of the loss cross sections σELrel ∼ const, to be compared with the Born asymptotic law σELB ∼ lnE/E.

Growth and Study of Scintillation Properties of Orthovanadate Crystals Ca:GdVO4 and Ca:YVO4

New scintillation orthovanadate crystals Ca:GdVO4 and Ca:YVO4 featuring intrinsic luminescence are grown. The spectra of pulsed cathodoluminescence of new scintillators and their luminescence decay time are studied. Using γ-rays with an energy of 662 keV from the 137Cs source, total absorption spectra (so-called photopeaks) for new orthovanadate crystals are measured. It is shown that the light yield of Ca:YVO4 and Ca:GdVO4 crystals is 28100 photon/MeV and 14000 photon/MeV, respectively.

The study of radiation degradation of optical properties of non-stoichiometric Lu3.01−xYxAl4.99O12 crystals doped with Ce3+, Cr3+, and Sc3+ ions under the action of gamma radiation

The spectra of pulsed cathodoluminescence (PCL) and optical transmission (OT) of crystals grown from Lu3.01−xYxAl4.99O12 melts doped with Cr3+, Ce3+, and Sc3+ ions before and after irradiation with gamma radiation of a 60Co radioactive source are studied. The gamma radiation dose absorbed by samples was 45 Mrad. The maximum gamma-radiation-induced absorbance in the range of 525–700 nm was 0.48 cm−1. Changes in the PCL and OT spectra of all samples after irradiation were detected. It was found that the relative intensity of Cr3+ bands increased after irradiation in relation to the Ce3+ band intensity by a factor of 1.6–8; the OT spectra of all samples after irradiation lost specific features and became identical. The results obtained are qualitatively explained. According to the explanation, the induced absorption is controlled first of all by optically active Frenkel defects formed after irradiation, which include an oxygen vacancy and an interstitial oxygen ion.

Coherent spectroscopy with fast frequency swept lasers

Effects caused by fast laser frequency sweeping across absorption lines are investigated. Oscillations in the time dependence of intensity of radiation generated by the medium, which are caused by beats between oscillations at variable excitation frequency and constant eigenfrequencies, are discovered. The time intervals between local maxima of the oscillations are inversely proportional to the difference between the eigenfrequency of the atomic oscillator and the instant frequency of the external radiation. The method of using fast frequency sweeping for determining indices of absorption at high optical densities (k0z ~ 100) is proposed.

On the angular momentum transfer upon excitation of electronic states of molecules by electrons of various energies

The intensities of lines IQ(1) and IQ(3) of the vibrational transition v′ = 0 → v″ = 0 of the Fulcher band system upon excitation of hydrogen molecules by an electron beam are measured. The beamelectron energy is ɛe = 15…30 eV (Δɛe ∼ 1 eV). The effective cross sections of H2 (d3Πu, v = 0) state excitation by electron impact are estimated both without changing themolecule angular momentum and with an appreciable angular momentum transfer. Processes with an appreciable angular momentum transfer are most efficient in the subthreshold excitation energy range (Ethr = 14 eV < Ee ≤ 18 eV) and are related to the formation of an intermediate composite system, i.e., a negative ion in the quasi-discrete state.

On the mechanism of angular-momentum transfer in electronic excitation of molecules by electron impact

Experiments on electron-impact vibronic excitation of molecular hydrogen in gas discharge plasmas and by electron beams reveal significant angular-momentum transfer and change in the ortho/para ratio. The observed effects are due to excitation via formation of negative intermediate ions. A model of such processes is proposed that provides a quantitative description of experimental results. The results of chi-square significance tests suggest that the dominant process is H2(X1Σg|) + e(p) → H2−(2Πu) → H2(d3Πu, I1Πg) + e′(l). The relative probabilities of ion decay by autodetachment of s, p, and other electrons are determined.

Isotope effects in the plasma-chemical decomposition of carbon dioxide

The carbon dioxide dissociation has been investigated both theoretically and experimentally in nonequilibrium plasma of the glow and microwave gas discharges. Vibrational and gas temperature values have been measured for molecules in plasma and the dissociation degree for the isotopes 12C16O2 and 13C16O2 after the exit of the gas from the reactor core has also been measured. CARS and absorption spectroscopy (with help of frequency tunable diode lasers) methods were used for the investigation.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.