Monochromatization of synchrotron radiation for nuclear resonant scattering experiments

An introduction to monochromatization of synchrotron radiation in the energy range of 5–30 keV is presented for applications involving nuclear resonant scattering. The relevant relationships of the dynamical theory of Xray diffraction are used to explain basic concepts of monochromatization. These relations are combined with raytracing techniques to design highenergyresolution monochromators. Transmissionoptimized and energyresolutionoptimized designs that achieve high energy resolutions (10⁶)< E/E < 10⁸) are discussed separately. Practical silicon monochromators of both types are presented for a variety of nuclear resonances in this energy range.     

Segregation of Components as a Result of High‐Power Laser Irradiation of Heterogeneous Condensed Media

The effects of periodic segregation of components in metastable (supercooled or supersaturated) binary alloys in the course of kinetic phase transformations as a result of laser irradiation of heterogeneous systems were studied analytically. Nonlinear processes of temporal and spatial selforganization of concentrationrelated structures were simulated using (i) a selfconsistent system of timedependent twodimensional equations for the distribution function for the sizes and spatial coordinates of the newphase particles and (ii) balance equations for the temperature and concentration of dissolved components; the latter equations account for nonlinearity of the particlesource function, sinks, for dependences of the phasetransition temperature on the surface curvature of particles and on the concentration of components, and for diffusive motion of particles in space. The domain of existence for the instabilities under consideration and the characteristics of the formed crystallizationrelated periodic structures are determined. It is established that nanoclusters formed during supersaturation of crystallizing material may play an important role in generation of selfoscillatory crystallization modes. Hydrodynamic aspects of liquidphase concentrationrelated stratification in heterogeneous systems based on immiscible components are considered.     

Manifestation of Extracoordination in the Resonance Raman Spectra of Water‐Soluble Cation Co‐Porphyrins

Resonance Raman spectra (RRS) of Co(II) and Co(III)5,10,15,20tetrakis(4Nmethylpyridinium)porphyrin ((Co^II(TmpyP4), and Co^III(TMPyP4)) in aqueous solutions at different pH as well as in organic solvents (methanol, ethanol, DMSO, DMF) are obtained. The increased sensitivity of the oscillation frequencies ₂, ₄, ₈, and ₆ — the markers of the oxidation state of a metal — to the nature of an axial ligand has been revealed. For Co^III(TmpyP4), the shifts of the indicated frequencies in extracoordination have turned out to be twofold larger than those for Co^II(TmpyP4). The spectral effects observed are related to different electron influence of the extraligands on the system of the porphyrin ring. In the case of Co(III)porphyrin, interaction of the d orbitals of the metal and the e _g ^*orbitals of the macrocycle is more efficient since its ionic radius is smaller than for the Co(II)complex. For Co^III(TmpyP4), a linear correlation between the oscillation frequencies ₂, ₄, ₈, and ₆ and the experimental Gutmann parameters characterizing the electronacceptor properties of solvents is found.     

Influence of Solvent Polarity and Viscosity on Nonradiative Processes in Oligothiophenes with Intramolecular Charge Transfer

By the methods of luminescence, picosecond spectroscopy, and quantumchemical calculations the mechanisms of electron excitation energy deactivation in some oligothiophenes with intramolecular charge transfer depending on the solvent polarity and viscosity have been investigated. While for 2Npiperidino5(2,2dicyanovinyl)thiophene (PDCVT) the main channel of nonradiative deactivation is the transition to a lower intermediate state with a twisted double bond controlled by the medium viscosity, in the case of (E){2[25piperidino2thienyl]6(trifluoridemethyl)4H4pyranylidene}propanedinitryl (PTFDN) fluorescence quenching is initiated by the solvent polarity. For two other oligothiophenes, 2Npiperidino5cyanothiophene (PCT) and 2Npiperidino5cyanoterthiophene (PCTT), differing in the length of the thiophene chain, we have revealed, along with the effective quenching of fluorescence in shortchain PCT (independent of the solvent polarity and viscosity), an increase in the radiation capacity in PCTT with increasing polarity of the solvent. The possible mechanisms of nonradiative deactivation in the investigated oligothiophenes are discussed.     

Theoretical Analysis of the Conformation of the Skeletal Base of Epoxysaccharide Molecules by the Vibrational Spectra

To explain the influence of the conformation of the skeletal base of the epoxysaccharide molecule on the frequencies and forms of normal vibrations, we have made a comparative theoretical analysis of the frequencies, forms, and potential energy distributions of normal vibrations in the 4001500 cm^–1 spectral range of five conformers of the epoxysaccharide methyl3,4anhydroD,Lallopyranoside molecule that approximate conformations of the hexapyranose rings close to the halfchair and boat forms. It is shown that a change in the structure of the molecule leads to frequency shifts and distortions of the forms of normal vibrations practically throughout the spectral range under consideration. The character of these changes is specific for different spectral ranges. The most sensitive to conformational changes in the pyranose ring are normal vibrations localized mainly within this ring, and the least sensitive ones are those localized on the bonds lying on the molecule's periphery. The frequency shift of normal vibrations comparable in form in the lowfrequency region in the series of conformers can reach 100 cm^–1. It is shown that the 650800 cm^–1 spectral range is the most convenient for identifying the form of the epoxypyranose ring. The changes in the force field associated with the conformation transitions of the pyranose ring are analyzed.     

Photostability of Molecules of Aromatic Amines in a Polymeric Matrix

In the temperature range T = 5–295 K, the spectralluminescent properties and curves of thermostimulated luminescence (TSL) of molecules of triphenylamine (TPA), trirtolylamine (TTA), triranisolamine (TAA), and N,N'diphenylbis(3methylphenyl)(1,1'biphenyl)4,4'diamine (TPD) in polystyrene and 4Brpolystyrene matrices have been investigated. It has been found that photoirradiation at room temperature in the region of the lowest electron transition of molecules leads to a decrease in the intensities of the luminescence, photoluminescence, and TSL bands, as well as to the formation of new deep traps for charge carriers. At equal irradiation doses these changes in TPD are noticeably less pronounced than in TPA, TTA, and TAA. The higher photochemical stability of TPD molecules compared to TPA, TTA, and TAA is attributed to the difference in the mechanisms of nonradiative deactivation of the triplet states of molecules.     

Stimulated Brillouin Scattering in the Midinfrared Region of the Spectrum

The behavior of opticalmedium parameters governing the efficiency of stimulated Brillouin scattering (SBS) with an increase in the pumpradiation wavelength is studied, and the range of media promising for accomplishing the phase selfconjugation in the course of SBS in the midinfrared region of the spectrum is determined. The SBS effect in the 10m region is realized experimentally in a fiber waveguide made of KRS5. The result obtained is in good agreement with the calculated SBS gain (0.14 cm/MW) and decay time of sound (200 ns) in KRS5. It is noted that the attainment of fairly high efficiencies of SBS reflection and phase selfconjugation for the abovethreshold intensities of excitation are controlled only by the level of technology for fabrication of fiber waveguides from infrared materials, the properties of which can still be much improved.     

Photodestruction of Zinc Complexes of Tetrabenzoporphyrins in a Polymeric Matrix and Photosensitive Materials Based on Them

At room temperature, a highefficiency photochromogenic reaction of destruction of Zntetra(4tertbutylbenzo)porphin molecules in a polyvinylbutyral matrix has been revealed. The linear dependence of the photobleaching rate of porphyrin on the irradiation power density is indicative of a singlephoton character of the reaction. The influence of pyridine and ethyl iodide additives as well as of intermolecular oxygen on the photodissociation rate of pigment molecules has been investigated. The most probable mechanism of transformation of the porphyrin compound is its photodestruction involving free radicals. We suggest using the composition as a photosensitive material, and we have determined its photosensitivity experimentally (S = 0.4·10³ cm²/J).     

On the Effect of Increasing the Radiative-Transition Rate Near a Nanosize Point

A short review of theoretical and experimental studies concerning the photoexcited florescence and Raman scattering of light for a substance in a space containing small material bodies is presented. Calculations of the radiativetransition probability for atoms (molecules) in the vicinity of bodies with a size much smaller than the light wavelength are performed. The probabilities of the singlephoton and doublephoton transitions are shown to increase by factors of 9 and 81 in the vicinity of a nanosize sphere with dielectric constant ||\ 1. The probability of a radiative transition in the vicinity of the vertex of a conic needle bearing up against a plane (both with || 1) increases by factors of (/R _in)² and (/R _in)⁴ for singlephoton and doublephoton transitions, respectively (R _in is the curvature radius for the needle vertex). This theoretical result is suggested as an explanation of the effect of increasing the radiation process intensity in the experiments carried out in the studies cited below.     

Influence of IR Radiation on the Electron Mobility in Submicron Layers of GaAs

The influence of optical radiation near the impurity absorption band on the electron mobility in submicron doped gallium arsenide layers formed on semiinsulating substrates is investigated. To determine the lowfield mobility of carriers, a method is used which is based on measurements of the mutual conductance and series resistances of a fieldeffect transistor at low sourcetodrain voltage. It has been established that the electron mobility increases under IR illumination as a consequence of decrease in electron scattering, and this is related to the photoneutralization of deeplying chrome acceptors.     

Spectral‐Luminescence and Generation Properties of 1‐Aza‐2‐Methyl‐6‐Aminopyrene and of Its Protolytic Forms

Spectral manifestations of protolytic forms of 1aza2methyl6aminopyrene in ethanol and aqueous solutions are investigated. The ionization constants of the protolytic forms are determined. The generation properties and photostability of a neutral molecule and a cation in excitation by an excimer XeCl laser are studied.     

Intramolecular Hydrogen Bond in Steroid 5‐Hydroxy‐6‐Ketones and 5‐Hydroxy‐6‐Ketoximes of the Stigmastane Series

The intramolecular hydrogen bond in steroid 5hydroxy6ketones and 5hydroxy6ketoximes of the stigmastane series has been investigated by the method of IR spectroscopy. It is shown that 5hydroxy groups in cisA/Bsteroids are linked by the intramolecular hydrogen bond with polar substituents at C₃ and C₆. These hydrogen bonds are lacking in corresponding transA/Bsteroids. According to the IR spectra, intramolecular associates of polymer type are formed in 5hydroxy6hydroxyminosteroids.     

Mössbauer effect and discovery of new hexagonal ferrites prepared at 980^\circ C

In the present article, undoped and Codoped Mtype Srhexaferrites have been prepared at low temperatures down to 980 C for the first time by the usual ceramic procedure and sintering technique. On these materials, a CoK Xray diffraction analysis and the room temperature ⁵⁷Fe Mössbauer spectroscopy (MES) were carefully performed. The results obtained are described and interpreted. The mechanism of Co substitution partially in place of iron and the site of its occupancy were proposed and established.     

Experimental verification of the theory of the successive production of striations in a glow discharge

The properties of the wave of stratification in the plasma of the positive column in a glow discharge in neon are measured. The measurements are compared with the results of the theory of the successive production of striations and good agreement is found.

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In conclusion the author thanks M. Novák for help in measuring and evaluating the experimental results, and F. Kroupa and V. Krejí for carefully reading this paper and for valuable remarks.     

Systems Approach to Optimization of the Regimen of Photodynamic Therapy of Solid Sarcoma M-1 Using the “Fotosens” Preparation as Example

A systems analysis of the interaction between objects (tumor, healthy tissue, radiation, and photosensitizer of the singlet state of oxygen) involved in photodynamic therapy was carried out. A schematic diagram of the biologically significative processes proceeding under these circumstances was proposed. This schematic diagram can serve as a basis for a systems approach to the optimization of photodynamic therapy. The efficiency of the systems approach in photodynamic therapy was demonstrated using Fotosens and Khlorin S preparations, carotene, and dodecaprene -carotene in biological experiments on Wistar rats and mouses inoculated for the solid sarcoma M-1.     

Procedure for Automated Measurement and Calculation of the Electrophysical Parameters of Solar Cells

We described the procedures for automated measurement and calculation of the electrophysical parameters of solar cells on the basis of the IBM PC, a solar radiation simulator, V721A digital voltmeters, and a programcontrolled potentiometer which ensure the programmed assignment of the load resistance in the range 0.002–15,000 and measurement of the light voltampere characteristics of the solar cells, a shortcircuit current, and the opencircuit voltage and also calculated the basic parameters of the solar cells, such as the efficiency, the fullfactor of the voltampere characteristics, optimum and maximum power, optimum load resistance, series and shunt resistance, and the matching factor for the ideal and experimental voltampere characteristic of the solar cells. The error in the measurement and calculation of the solar cell parameters does not exceed 0.2%.     

Heterogeneous Chemiluminescence of Crystal Phosphors on X‐Ray or UV Irradiation

Using a highvacuum assembly with molecular beams and setups with an implemented atom probe, we investigated atomic and molecular adsorption luminescence of the oxides CaOBi and MgO in O and O₂ beams and also radicalrecombination luminescence excited by H and O atoms in ZnS and in ZnS,CdS samples activated with silver, copper, and the rareearth element Tm. It is established that exposure to UV light and xray radiation of the CaOBi, MgO, and ZnSTm samples, where the mechanism of direct excitation of heterogeneous chemiluminescence (HCL) is realized, does not influence the characteristics of the heterogeneous chemiluminescence, whereas similar exposure of the ZnS,CdSCu,Al and ZnS,CdSAg samples and of selfactivated ZnS, in which the excitation of heterogeneous chemiluminescence is due to the ionization of the lattice, leads to an increase in the intensity of heterogeneous chemiluminescence up to five orders of magnitude. The mechanisms of the phenomenon are considered.     

Poloidal Magnetic Field Measurements in a Reversed Field Pinch Plasma by a Far‐Infrared Polarimeter

A multichannel farinfrared (FIR) polarimeter has been installed in RFX, a Reversed Field Pinch (RFP) plasma experiment, to measure the poloidal magnetic field profile. The polarimeter uses a CH₃OH FIR laser operating at =118.8 m. Faraday rotation measurements on five of six parallel diagnostic chords are used in preliminary investigations of poloidal field profiles. The experimental results are generally found in good agreement with the &p model predictions. The choice of the profile of = ₀ j·B/B² is discussed. For the reconstruction of the magnetic field profiles a numerical filamentary current equilibrium code is described, where polarimetric data are included as constraints. An alternative method based on the bestfit of a threeparameter profile to the polarimetric data is also reported. Both methods provide reliable reconstructions of the plasma magnetic field and the results indicate the existence in RFX of hollow profiles.     

Radiative Losses of Plasma on Interaction of Ultrashort Laser Pulses with Matter

Radiative losses of plasma produced by ultrashort laser pulses near the surface of solid targets were studied by the methods of highresolution xray spectroscopy and using the numerical simulation of gasdynamics and radiation processes. The experiments were carried out at the NEODIM laser facility in the Central Research Institute for Machine Building. The flux density was as high as 10¹⁷ W/cm² when the radiation was focussed onto the surface of solid targets from Al and Cu. The timeintegrated discrete spectra of plasma of the multiply charged ions were recorded in the soft xray band from 0.8 to 3.0 keV. The experimental spectra were compared with the results of numerical calculations within the framework of the model, which considered both hydrodynamic and radiationcollisional processes. The association of the radiation dynamics of the individual groups of lines with the spatial and temporal dynamics of the laser torch was revealed. Such an association permits one to judge the nonstationary processes in the expanding plasma even by the spectra integrated over time. From comparison of the experimental results and model calculations, it follows that the line emission of a relatively narrow (in the charge number) group of ions constitutes the major portion of radiation losses.     

EPR and Thermoluminescence in ZnO Single Crystals with Anionic Vacancies

The radiation defects created in hydrothermal ZnO–Li single crystals by irradiating them with electrons, protons, and highenergy ions have been investigated. The anionic vacancies (Fcenters) in ZnO are established to be the centers of radiationless recombination of the charge carriers with a photoionization energy of 2.3 eV (a signal of the photoEPR with the gfactor for the F⁺center: g = 1.9948 and g = 1.9963). The anionic vacancies in the form of the F and F⁺ states are a good reference of the electron and hole processes. The [F_Li]^×centers that correspond to the oxygen vacancies localized near the point defects Li_Zn are detected. In the temperature range 530–660 K, ZnO crystals display thermally stimulated processes such as the healing of anionic vacancies (530–630 K) and the disappearance of the [F_Li]^×centers (610–660 K).