Radiation of channeled 800 MeV electrons in diamond crystals

Measured data on γ-ray emission for the low-energy region of the bremsstrahlung spectra produced by 800 MeV electrons in diamond crystals are presented. The obtained spectral and orientational characteristics of the γ-ray yield indicate that the low-energy radiation is associated with the channeling of electrons.     

Generation of picosecond optical phase conjugate pulses using cw mode-locked lasers

Low power picosecond optical phase conjugation has been demonstrated using cw mode-locked argon-ion and dye lasers via 4-wave mixing in ruby. Streak camera and power measurements show that the generated pulses are identical to the input pulses.     

PHOTOPHYSICAL BEHAVI0RS OF OLIGOMER BASED ON 1, 1′-BINAPHTHOL WITH 3, 3′-ACETYLENE SPACER*

The photophysical behaviors of the oligomer based on 1,1'-binaphthol with3,3'-acetylene spacer were investigated. The oligomer molecule has a naphthyl-acetylene-naphthyl effective conjugation segment. The atropic of the 1,1'-binaphthyl moiety led totwisted and rigid main chain in the oligomer. With the changes of the external environ-ment such as solvents used, solvent viscosity and ambient temperature, the wavelengthsof absorption and the intensities of fluorescence and absorption are changed slightly, butthe fluorescent intensity and quantum yield can be influenced. The luminescent behav-iors of the oligomer exhibit twisted intramolecular charge transfer characteristics, whichcould have a potential application in wavelength-stable light emitting material adaptableto ambient temperature and the solvents used in wide range.     

Ammonia and carbon dioxide permeability through perfluorosulfonic membranes

Transmembrane transport of ammonia and carbon dioxide through perfluorosulfonic membranes in ionic forms of transition metals was studied in a wide temperature interval. The different patterns of the temperature plots of the permeability coefficient of ammonia were found for different ionic forms of the membrane. An increase in the ammonia permeability with an increase in the moisture contents of the membrane also depends on its ionic form. The effects observed are explained by the different structures of water—ammonia complexes formed with metal ions. The mechanism of transmembrane transport of ammonia through perfluorosulfonic membranes in various ionic forms is discussed.     

Tuning Pore Size in Square‐Lattice Coordination Networks for Size‐Selective Sieving of CO2

Porous materials capable of selectively capturing CO₂ from flue‐gases or natural gas are of interest in terms of rising atmospheric CO₂ levels and methane purification. Size‐exclusive sieving of CO₂ over CH₄ and N₂ has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore‐size in a coordination network, [Cu(quinoline‐5‐carboxyate)₂]_n ( Qc‐5‐Cu ) ena+bles ultra‐high selectivity for CO₂ over N₂ (S_CN≈40 000) and CH₄ (S_CM≈3300). Qc‐5‐Cu‐sql‐β , a narrow pore polymorph of the square lattice ( sql ) coordination network Qc‐5‐Cu‐sql‐α, adsorbs CO₂ while excluding both CH₄ and N₂. Experimental measurements and molecular modeling validate and explain the performance. Qc‐5‐Cu‐sql‐β is stable to moisture and its separation performance is unaffected by humidity.     

Measurement of the production cross section for charmed baryons in proton–nucleus interactions at 70 GeV

The results of an analysis of data from the SERP-Е-184 experiment devoted to studying mechanisms of the production of charmed particles in proton–nucleus interactions at 70 GeV and their decays are presented. The data in question were obtained upon irradiating the SVD-2 active target consisting of carbon, silicon, and lead plates with a beam of 70-GeV protons. A detailed simulation on the basis of the FRITIOF7.02 and GEANT3.21 code packages made it possible to optimize event-selection criteria and to calculate the detection efficiency for Λ_c⁺ baryons. After selecting a signal from the threebody decay of a Λ_c⁺ baryon, the inclusive cross section for its production at near-threshold energies, its lifetime, and the parameter of the A dependence of the cross section were found. The Λ_c⁺ -baryon yields are tabulated along with data from other experiments and theoretical predictions.     

Use of thin collodion films to prevent recoil-ion contamination of alpha-spectrometry detectors

Recoil ions from alpha-particle emission can contaminate surface-barrier detection systems. This contamination results in increased measurement uncertainty, and may require the replacement of expensive detectors. Disposable thin Collodion films are easily prepared and effectively retard the recoil ions when either directly applied to the surface of alpha-sources or as catcher foils between the source and the detector. The thin films are particularly effective for relatively low-level sources, but can sustain structural damage when exposed to high levels of recoil ions (tens of thousands per second) over extended periods of time.     

Positron annihilation and Hall effect in electron irradiatedn-InP crystals

Positron annihilation and Hall effect inn-InP crystals as a function of electron irradiation up to 1 · 10¹⁹ cm^–2 and post-irradiated isochronal annealing up to 550 °C have been studied. It is concluded that in irradiatedn-InP samples positrons interact with negatively charged acceptor-type defect with level atE _c –0.33 eV, probablyV _In (primary defect). In post-irradiated isochronal annealed (up to 330 °C) samples ofn-InP positron trapping occurs preferably in secondary defects-vacancy clusters, which are formed in the temperature range (150–300 °C). Inn-InP crystals containing radiation induced defects the trapping rate was found to decrease with temperature in the range (300–77) K.     

Obstructions to the equivalence of Poisson structures near a symplectic leaf of semisimple and compact type

We describe cohomological obstructions to the equivalence of Poisson structures around a symplectic leaf of semisimple and compact type. The result is based on Conn’s linearization theorem and the theory of Poisson coupling.     

Study of the Au/SiO<Subscript>2</Subscript> + Co(65 at %)/GaAs heterostructure interfaces by the polarized neutron reflectometry method

Using the polarized neutron reflectometry method, we studied Au/SiO₂ + Co(60 at %)/GaAs granular films, which display a giant injection magnetoresistance effect in a narrow temperature range close to T = 300 K. We revealed the existence of a layer having particular magnetic properties at the boundary of a film with a semiconductor GaAs substrate. Experiments carried out at temperatures T = 300 K and T = 100 K showed an insignificant difference in the magnetic profile of the heterostructure.