Optical Spectra of Gamma-Irradiated LiF Crystals with Anisotropic Lithium Nanoparticles

The optical response of Li anisotropic defects and nanoparticles from three faces of cubic LiF crystals with 10-mm edges to γ radiation from a ⁶⁰Со source with doses of 10⁵–10⁹ R at 320 K in air is studied. After a maximum dose of 10⁹ R, scanning electron microscopy revealed submicron metal lithium flakes ordered into long parallel nanofilaments. The resonance absorption band, which shifts from 272 to 295 nm with increasing dose, is assigned to lithium nanocolloids in the (110) plane. The band at 202–225 nm observed only from the (100) face narrows at doses below 10⁵ R and is assigned to diatomic fluorine molecules in interstitial sites. The appearance of the 209–212–215-nm triplets at 2.7 × 10⁵ R from the (100) plane and the 211–213–215-nm triplets at 0.9 × 10⁵ R from the (010) plane is related to radiation-induced axially symmetric bipolarons with a high oscillator strength. The splitting of the 445-nm band into a 438–445–450-nm triplet is observed only for the (010) plane after a dose of 10⁶ R and is related to surface plasmon polaritons (longitudinal and transverse) of elongated Li nanoparticles. The (F₂–F₃) complexes are oriented in the most imperfect (111) plane and are seen along three cubic axes.     

Effect of residual atmospheric pressure on the development of electrostatic discharges at the surface of protective glasses of solar cells

Electrostatic discharges obtained upon the irradiation of K-208 glass with 40-keV electrons at a flux density φ of 10¹⁰ to 2 × 10¹¹ cm^–2 s^–1 are studied. The residual pressure p _v in the vacuum chamber is varied from 5 × 10^–5 to 5 × 10^–3 Pa. Structural changes in the sample surfaces are studied by atomic-force microscopy. Depending on the pressure level, two types of discharges are observed in experiments at 3 × 10¹⁰ ≤ φ ≤ 1.2 × 10¹¹ cm^–2 s^–1: a microprojection at the glass–ionized-residual-atmosphere surface and a discharge which develops along the irradiated surface. It is found that at 5 × 10^–5 ≤ p _v ≤ 3 × 10^–4 Pa and 8 × 10¹⁰ ≤ φ ≤ 10¹¹ cm^–2 s^–1, discharges of the first type appear at the beginning of exposure; that is, an increase in microprojections is observed. Further, surface discharges propagate through these microprojections. At 10^–3 ≤ p _v ≤ 5 × 10^–3 Pa and 10¹⁰ ≤ φ ≤ 5 × 10¹⁰ cm^–2 s^–1, on the contrary, discharges of the second type are realized at the beginning. These discharges result in the appearance of channels with inhomogeneities on the glass, at which subsequently discharges of the first type occur. It is determined by calculations that in the region adjacent to the exposed glass surface, secondary electrons accelerated in a field of charge accumulated in the glass make the main contribution to the ionization of gases.     

Emission spectrum of concentrated dye solutions excited by high-power laser radiation

Emission spectra of concentrated (~10¹⁸–10¹⁹ cm^–3) ethanol solutions of Rhodamine C excited by high-power (~10²⁵–10²⁶ cm^–2s^–1) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm^–1). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.     

Fraction of protons in primary cosmic rays according to data from the PAMIR experiment in consideration of the response of X-ray emulsion chambers

Adjusted data on the fraction of protons in the mass composition of primary cosmic rays (PCRs) in the energy range of 10¹⁵–10¹⁷ eV are presented. Adjustments are made according to detailed calculations of the response of the X-ray emulsion chamber in the PAMIR experiment. It is demonstrated that the fraction of protons in a PCR is 16–18% for E ₀ ≈ 10¹⁵–10¹⁶ eV and does not change within the error for E ₀ ≈ 10¹⁶–10¹⁷ eV.     

Enhancement of Fluorescence of Nanosized ZnO: SiO<Subscript>2</Subscript> Films in the Presence of Human Serum Albumin

The optical properties of the films of new nanosized of ZnO: SiO₂ materials with intense ultraviolet luminescence (UVL) with a maximum at 362 nm were studied. When human serum albumin (HSA) is applied on the surface of films, an effective fluorescent energy transfer occurs, which is manifested in an increase in the intensity of ultraviolet luminescence of ZnO: SiO₂. The increase in integrated UVL intensity is inversely proportional to HSA concentration; it has 9.2–12.6 times (with a decrease in the HSA concentration from 10^–8 to 10^–12 M) the UVL intensity of purified ZnO: SiO₂ film. The dependence of the UVL intensity on the HSA concentration is close to linear. Compared to the intensity at a concentration of 10–8 M, the gain is 8, 19, 31, and 36% for protein concentrations in the solution applied to the surface of ZnO: SiO₂ of 10^–9, 10^–10, 10^–11, and 10^–12 M, respectively. These supramolecular systems can be used to create biosensors and to simulate the physicochemical processes of photosynthesis. In the former case, the linear dependence of fluorescence on concentration is a significant advantage.     

On the creation of ordered nuclei by ion bombardment for obtaining nanoscale si structures on the surface of CaF<Subscript>2</Subscript> films

The effect of preliminary low-energy (~1 keV) and low-dose (~10¹²–10¹⁴ cm^–2) ion bombardment on the initial stages of growth of Si films on a CaF₂/Si surface is investigated. Ordered nanocrystal phases (thickness less than 5–6 monolayers) and homogeneous epitaxial nanofilms (thickness more than 8–10 monolayers) of silicon are shown to be formed after annealing.     

Ramp compression of tantalum to 330 GPa

We report on the stress–density and rate-dependent response for Ta, ramp compressed to 330?GPa with strain rates up to 5?×?10⁸?s^?1. We employ temporally shaped laser drives to compress Ta stepped foils over several to tens of nanoseconds. Lagrangian wave-profile analysis reveals a stress–density relationship which falls below the Hugoniot, above the hydrostat, and is consistent with ramp-compression experiments at lower strain rates. We also report on the peak elastic stress prior to plastic deformation as a function of strain rate for laser-driven ramp and shock-compression data spanning the 1–50?×?10⁷?s^?1 strain-rate range. When combined with previously published lower strain data (10¹–10⁷?s^?1), we observe a change in rate dependence, suggesting a transition from thermally activated to defect-limited (phonon drag) dislocation motion occurring at a strain rate of about 10⁵?s^?1.     

Ionic conduction of γ-titanium phosphate in hydrogen and alkali metal salt forms

Impedances of compact discs of anhydrous γ-titanium phosphate and some ofits salt forms were measured in the temperature range of 100–300°C, while the corresponding hydrated forms were investigated between -20 and +25°C. Either at low or high temperature the impedance plots are consistent with a parallel combination of a conductance, a capacitance and a constant phase angle admittance. Anhydrous compounds have lower conductivities (σ_300°C=10^-4–10^-6ω^-1cm^-1) and higher activation energies (E_a = 13.9–20.7 kcal/mol) than those of the corresponding hydrated ones (σ_25°C = 10^-3–10^-5ω^-1cm^-1 and E_a = 2–10 kcal/mol); however, in both cases, the activation energy increases with increasing ionic radius. The values of the ion diffusion coefficients for hydrated forms (10^-8–10^-9 cm²/s), computed at 25°C by the Nernst-Einstein equation, are considerably higher than those obtained by self diffusion experiments. This seems to indicate that the conductivity is essentially due to hydrated cations present on the surface of the microcrystals.     

RX J0720.4-3125 as a possible example of magnetic field decay in neutron stars

We consider the possible evolution of the rotation period and magnetic field of the X-ray source RX J0720.4-3125, assuming that this source is an isolated neutron star accreting from the interstellar medium. The magnetic field of the source is estimated to be 10⁶–10⁹ G (the most probable value is about 2·10⁸ G), and it is difficult to explain the observed rotational period 8.38 s without invoking the hypothesis of magnetic field decay. For calculations we used the model of ohmic dissipation of the field in the core of the neutron star. Estimates for the accretion rate (10^?14–10^?16 M_⊙/yr), velocity of the source through the interstellar medium (10–50 km/s), and neutron star age (2·10⁹–10¹⁰ yrs) are obtained.     

Electrical Conductivity of Noble Gas Plasmas in the Warm Dense Matter Regime

The electrical conductivity of noble gas plasmas is investigated by using the relaxation‐time approximation in the density range 10^–5–10 g cm^–3 and temperature range 10⁴–10⁵ K. The electrical conductivity calculated shows reasonable consistency with shock wave experiments and theoretical simulations at above 2 × 10⁴ K where the Coulomb interaction dominates. A nonmetal to metal transition in helium plasma is predicted at 2.4 g cm^–3 and shown reasonable agreement with the most recent shock wave experiment (above 1.9 g cm^–3). Furthermore, the insulator‐metal transition densities of all the noble gas plasmas are predicted and compared with available results (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microwave electrophysical properties of superionic crystals Ag2HgI4

The paper concerns itself with the investigation results of temperature dependencies of electric conduction and dielectric properties of Ag₂Hgl₄ crystals in the frequency range of 10⁷–7,8·10¹⁰ Hz. The obtained data have shown that in α-phase at T=326 K, the electric conductivity σ is proportional v^0,28 in the frequency range of 10⁷–10⁹ Hz and σ is proporti onal v^0,5 in the range of (1,1–78)·10⁹ Hz. The dependence σ(v) in the range of (1,1–78)·10⁹ Hz may be conditioned by the jumping mechanism of the conductivity and low frequency oscillations of the crystal lattice. It is believed, tha in the σ-phase of Ag₂Hgl₄ a condition of the existence of the ionic polaron is satisfied. The activation energy of the polaron is ΔE_p=0,09 eV.     

Cross sections and thermonuclear reaction rates of proton-induced reactions on 37Cl

The yields of γ-rays from the reactions ³⁷Cl(p, γ)³⁸Ar and ³⁷Cl(p, αγ)³⁴S have been measured as a function of bombarding energy over the ranges 0.65–2.15 MeV and 1.25–2.15 MeV respectively, and the yield of neutrons from ³⁷Cl(p, n)³⁷Ar from threshold to 2.50 MeV. The results are compared with global statistical-model calculations and thermonuclear reaction rates are calculated for the temperature range 5 × 10⁸–10¹⁰ K. The significance of these thermonuclear reaction rates for stellar nucleosynthesis calculations is discussed.     

A model for the spectral line polarization shift in dense plasma

The plasma polarization shift (PPS) of spectral lines from hydrogenic ions immersed in a dense hydrogen plasma is examined by using an interaction model that includes the effects of perturbers exterior to the bound electron orbit. The semiclassical model is compared with (a) experimental shifts of Paschen lines in He⁺ at densities of 10¹⁶–10¹⁷ cm^?3 and temperatures of a few eV and (b) self-consistent potential calculations for Lyman α in Ne⁺⁹ and Ar⁺¹⁷ at densities of 10²⁴–10²⁵ cm^?3 and temperatures of 500–2000 eV.     

Relaxation of vibrationally excited reaction products in a crystal lattice

The relaxation of vibrationally excited nitrogen molecules in the matrix of silver azide is studied. The effective rate constants for the interaction of an excited nitrogen molecule with free charge carriers (1.7 × 10^–10 cm³ s–1) and for the generation a hole from the level of the produced defect at the expense of the vibrational energy of the molecule (3 × 10¹⁰ s^–1) are estimated. An associative–dissociative mechanism of the deactivation is proposed, which consists in the capture of an electron onto the level of the produced defect with the subsequent emission of an electron into the conduction band at the expense of the vibrational energy of the excited molecule. The effective rate constants for electron emission from the excited level of a hydrogen-like defect at values of the principal quantum number of 3 and 4 are estimated as 1.8 × 10⁹ and 2.8 × 10⁹ s^–1, respectively. Based on the processes considered, an expression for the probability of chain propagation is obtained.     

Ion-beam erosion of carbon fibers of the composites

The results of experimental studies of the structural and morphological changes of the surface of carbon PAN fibers of a carbon-carbon KUP-VM (1D) composite as a result of high-dose irradiation (10¹⁸–10¹⁹ ion/cm²) with Ne⁺ and Ar⁺ ions with an energy of 10–30 keV are presented. The threshold values of radiation damage, resulting in an amorphization of the PAN carbon fibers at room temperature and ion-induced crimping at temperatures greater than the annealing temperature of the radiation damage, are determined.     

Enhanced radiation hardness of ZnO nanorods versus bulk layers

It is shown that ZnO nanorods grown by MOCVD exhibit enhanced radiation hardness against high energy heavy ion irradiation as compared to bulk layers. The decrease of the luminescence intensity induced by 130 MeV Xe⁺²³ irradiation at a dose of 1.5 × 10¹⁴ cm^–2 in ZnO nanorods is nearly identical to that induced by a dose of 6 × 10¹² cm^–2 in bulk layers. The change in the nature of electronic transitions responsible for luminescence occurs at an irradiation dose around 1 × 10¹⁴ cm^–2 and 5 × 10¹² cm^–2 in nanorods and bulk layers, respectively. High energy heavy ion irradiation followed by thermal annealing is also effective on the quality of ZnO nanorods grown by electrodeposition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental Study and Modelling of Formation and Decay of Active Species in an Oxygen Discharge

A microwave (2.45 GHz) oxygen discharge (3 hPa, 150 W, 50 mL.min^–1) is studied by optical emission spectroscopy of O(⁵P) (line 777.4 nm) and of the atmospheric system of O₂(head‐line 759.4 nm). Calibration of the spectral response of the optical setup is used to determine the concentrations of O(⁵P) and O₂(b). The concentration of the O(⁵P) atoms is in the range 108–109 cm^–3 and the concentration of the O₂(b) molecules is in the range 10¹⁴ – 2 × 10¹⁴ cm^–3 along the discharge tube. An attempt is made to simulate the experimental results by using coupling the Boltzmann equation, homogeneous energy transfer V‐V and V‐T, heterogeneous reactions on the walls (energy transfer and recombination of atoms) and a kinetic scheme (electronic transfer and chemical reactions). The Boltzmann equation includes momentum transfer, inelastic and superelastic processes and e‐e collisions. V‐V and V‐T transfer equations are obtained from the SSH theory and the kinetic scheme includes 65 reactions with 17 species [electrons e, ions O^– and O₂^–, fundamental electronic neutral species O(³P), O₂, O₂(X,v), O₃ and excited neutral species O₂(a), O₂(b), O₂(A), O(¹D), O(¹S), O(⁵P), O(4d ⁵D^o), O(5s ⁵S^o), O(3d ⁵D^o) and O(4s ⁵S^o)]. A fair agreement between experimental results and modelling is obtained with the following set of fitting values: – heterogeneous deactivation coefficient for O₂(b) γ = 2.6 × 10^–2; – rate constant of reaction [O(¹D) + O(³P) → 2 O(³P)] k₃₄ = 1.4 × 10^–11 cm³.s^–1; – electron concentration in the range 10¹⁰ – 10¹¹ cm^–3. Modelling shows that the recombination coefficient for oxygen atoms on the silica wall (range 1.4 × 10^–3 – 0.2 × 10^–3) is of the same order as the values obtained in a previous paper and that the ratio ([O] / 2 [O₂]initial) is about 33–50%. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Concept of the Fourth-Generation Neutron Source in Dubna

The principles of designing a subcritical neutron-multiplying system with reactivity modulation, which can be used as the target in a superbooster with a linear proton accelerator, are described. Calculations demonstrate that the output neutron-flux density of a pulse can be expected to reach 10¹⁷ cm^–2 s^–1 at maximum and 2 × 10¹⁴ cm^–2 s^–1 on average. The pulse duration of thermal neutrons can be 200–300 and 20–30 μs depending on the moderator and the corresponding pulse duration of the proton accelerator.     

Microwave to X ray up-conversion by undulated electron beams

The device previously known as “free electron laser” is shown to act in some kinematical conditions as a radiation up-converter and amplifier. Its application to the presently available electron beams allows the production of tunable coherent radiation in the range 10¹⁰–10¹⁹ Hz (10^-4–10^-5 eV).     

Crystalline and optical properties of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S (0.5 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 1) films doped with silver

The results from studying Cd _x Zn_1–x S (0.5 ≤ x ≤ 1) films fabricated via pyrolysis from thiourea coordination compounds of cadmium and zinc bromides doped with silver ions having impurity concentrations of 10^–7, 10^–6, 10^–5, 10^–4, and 10^–3 mol L^–1 in sputtered solutions are presented. Films prepared at 400°С have the wurtzite lattice. The bandgap of pure and doped films, determined from absorption spectra near the edge of fundamental absorption, varies linearly from 2.5 to 3.11 eV. An order of magnitude increase in the intensity of luminescence is observed after doping with silver.