Influence of the rhenium carrier in eluate of Re-188 on its binding with potassium-sodium salt of hydroxyethylidene biphosphonic acid

The results of investigation of the regularity of ¹⁸⁸Re binding with KNaHEDP and hydrolysis of the complex compound (¹⁸⁸Re-KNaHEDP) have shown that its quality depends to a considerable extent on the reaction conditions. Concentrations of a reducing agent (Sn²⁺) and stable rhenium in the ¹⁸⁸Re eluate, as the carrier, influence essentially the rate of formation and stability of ¹⁸⁸Re complex with KNaHEDP. The results of the kinetic investigations of the ¹⁸⁸Re-KNaHEDP complex formation prove that the reaction character bears a direct relationship to the concentrations of the complexing agent (Re) and the reducer (Sn²⁺). The higher ratio of Re⁷⁺: Sn²⁺ concentrations, the more effectively ¹⁸⁸Re binds with KNaHEDP. The obtained results prove that for ¹⁸⁸Re binding with KNaHEDP with the efficiency not less than 95% the optimum concentration of stable rhenium in the reaction mixture is 0.54×10⁻⁶ mol·ml⁻¹ (0.1 mgMml⁻¹) and the ratio of Re⁷⁺: Sn²⁺ concentrations should not be lower than 10: 1.     

Initiation of combustion of a methane-air mixture in a supersonic flow behind a shock wave during laser excitation of O<Subscript>2</Subscript> molecules

The possibility of initiating detonation of CH₄ + air in a supersonic flow behind an oblique shock wave under the exposure of the mixture to laser radiation with wavelengths λ_I=1.268 μm and 762 nm is analyzed. It is shown that this irradiation leads to excitation of O₂ molecules to the a ¹Δ_g and b ¹Σ _g ⁺ states, which intensifies the chain mechanism of combustion of CH₄/O₂ (air) mixtures. Even for a small value of the laser radiation energy absorbed by an O₂ molecule (∼0.05–0.1 eV), detonation mode of combustion in a poorly inflammable mixture such as CH₄/air can be realized at a distance of only 1 m from the primary shock wave front for relatively small values of temperature (∼1100 K) behind the front under atmospheric pressure.     

Numerical simulations of pulsating detonations: II. Piston initiated detonations

Extremely long time, high-resolution one-dimensional numerical simulations are performed in order to investigate the evolution of pulsating detonations initiated and driven by a constant velocity piston, or equivalently by shock reflection from a stationary wall. The results are compared and contrasted to previous simulations where the calculations are initiated by placing a steady detonation on the numerical grid. The motion of the piston eventually produces a highly overdriven detonation propagating into the quiescent fuel. The detonation subsequently decays in a quasi-steady manner towards the steady state corresponding to the given piston speed. For cases where the steady state is one-dimensionally unstable, the shock pressure begins to oscillate with a growing amplitude once the detonation speed drops below a stability boundary. However, the overdrive is still being degraded by a rarefaction which overtakes the front, but on a time-scale which is very long compared with both the reaction time and the period of oscillation. As the overdrive decreases, the detonation becomes more unstable as it propagates and the nature (e.g. period and amplitude) of the oscillations change with time. If the steady detonation is very unstable then the oscillations evolve in time from limit cycle to period doubled oscillations and finally to irregular oscillations. The ultimate nature of the oscillations asymptotically approaches that of the saturated nonlinear behaviour as found from calculations initiated by the steady state. However, the nonlinear stability of the steady detonation investigated in previous calculations represents only the very late time (O(10⁵) characteristic reaction times) behaviour of the piston problem.     

Initiation of a detonation wave by resonant laser radiation in a hydrogen-oxygen mixture flowing about a wedge

The formation of an oblique detonation wave in a supersonic hydrogen-oxygen flow about a planar wedge is considered. It is shown that the excitation of the electronic state b ¹Σ _g ⁺ in oxygen molecules by resonant laser radiation with a wavelength of 762 nm makes it possible to initiate detonation combustion at a distance of ≈1 m from the tip of the wedge at low temperatures (500–600 K). Notably, it suffices to irradiate the gas in the narrow (0.5–1.0 cm across) paraxial region of the flow near the tip of the wedge. It is found that the laser-induced excitation of molecular oxygen is several times more efficient than ordinary heating of the mixture to initiate a detonation wave.     

Transverse wave generation mechanism in rotating detonation

Detonation engines are expected to be included in a number of aerospace thrusters in the future. Several types of detonation engines are currently under examination, including the rotating detonation engine (RDE). Although the RDE has been explored experimentally, its rotating detonation propagation mechanism is not well understood. This paper clarifies the detonation mechanism and dynamics of the RDE by 2D and 3D simulation using compressible Euler equations with a full chemical reaction mechanism of H₂/O₂ and H₂/Air, especially from the triple-point and transverse detonation points of view. A total variation diminishing (TVD) scheme is used for the mixture of H₂/Air, and an advection upwind splitting method difference vector (AUSMDV) scheme is used for the mixture of H₂/O₂. The use of an AUSMDV scheme provides a much clearer detonation structure than does the TVD scheme. We focus on the complex interaction mechanism of the detonation front and burned mixture gases. We found out that at this interaction point, an unreacted gas pocket appears and ignites periodically to generate transverse waves at the detonation front and maintain detonation propagation.     

Photoconduction in tunnel-coupled Ge/Si quantum dot arrays

The photoconduction in a tunnel-coupled Ge/Si quantum dot (QD) array has been studied. The photoconductance (PC) sign can be either positive or negative, depending on the initial filling of QDs with holes. The PC kinetics has a long-term character (10²?10⁴ s at T = 4.2 K) and is accompanied by persistent photoconduction (PPC), whereby the PC value is not restored on the initial level even after relaxation for several hours. These phenomena are observed upon illumination by light with photon energies both greater and smaller than the silicon bandgap. A threshold light wavelength corresponding to a long-term PC kinetics depends on the QD filling with holes. A model describing the observed PC kinetics is proposed, according to which the main contribution to the PC is related to the degree of QD filling with holes. By applying the proposed model to the analysis of PC kinetics at various excitation levels, it is possible to determine the dependence of the hopping conductance on the number of holes per QD. The rate of the charge carrier density relaxation exponentially depends on the carrier density.     

Temperature dependence of the nuclear quadrupole interaction and the Knight shift in rhenium metal

The temperature dependences of the static nuclear quadrupole interaction and the Knight shift in rhenium metal were investigated for 2K ≦ T ≦150 K by the method of Nuclear Acoustic Resonance (NAR). For the quadrupole interaction ¦e²qQ/h¦ an increase occurs from 255.2(5) MHz at 2 K to 257.2(8) MHz at 150 K in¹⁸⁷Re [269.5(7) to 271.5(10) in¹⁸⁵Re] whereas for the Knight shift a slight decrease from 1.14(4)% at 2K to 1.10(8)% at 150 K [1.16(6) to 1.12(10)] is found.     

Formation of a detonation wave in the thermal decomposition of acetylene

The formation of a condensation detonation wave has been experimentally observed in the shock-induced thermal decomposition of acetylene. The stable detonation wave in the 20% C₂H₂ + 80% Ar mixture has been obtained at an initial pressure behind the shock wave of no less than 30 atm. The main kinetic characteristics of the pyrolysis of acetylene—the period of the induction of condensation and the growth rate constant of condensed particles—have been determined. The correlation of various stages of the process with the heat release in the condensation has been analyzed. It has been shown that the period of the particle growth induction is not accompanied by noticeable heat release. The subsequent condensation stages characterized by significant heat release occur very rapidly (faster than 10⁻⁵ s) in the so-called explosive condensation. The analysis of the results indicates that the reactions leading to the growth of large polyhydrocarbon molecules, which precede the formation of condensed carbon particles, constitute the limiting stage of the process, which determines the possibility of the formation of the condensation detonation wave in acetylene. An increase in the pressure is accompanied by the sharp narrowing of the induction region and the transition of the process to the condensation detonation wave.     

Kinetics of the photoconductivity and absorption in the D −(A +) bands in doped silicon

The photoconductivity (PC) spectra and the induced absorption of background radiation in the energy range 10–40 meV are investigated in weakly compensated B-, Ga-, and As-doped silicon at 4.2 K. It is shown that dips corresponding to the photoionization of long-lived excited states of B and As are observed in the PC spectra on the D ⁻(A ⁺) bands. It is found that the frequency dependence of the PC spectra corresponds to excitation relaxation times of the order of 10⁻⁴ s for the states in the D ⁻ (A ⁺) bands. It is established that in electric fields E>100 V/cm the PC decreases sharply, while the induced absorption of the background radiation changes very little. This confirms the conclusion that the excitation of the D ⁻ (A ⁺) itself makes the main contribution to the PC. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 224–227 (25 August 1997)     

In situ study of self-ion irradiation damage in W and W–5Re at 500 °C

In situ self-ion irradiations (150?keV?W⁺) have been carried out on W and W–5Re at 500?°C, with doses ranging from 10¹⁶ to 10¹⁸ W⁺m^?2 (～1.0?dpa). Early damage formation (10¹⁶W⁺m^?2) was observed in both materials. Black–white contrast experiments and image simulations using the TEMACI software suggested that vacancy loops were formed within individual cascades, and thus, the loop nucleation mechanism is likely to be ‘cascade collapse’. Dynamic observations showed the nucleation and growth of interstitial loops at higher doses, and that elastic loop interactions may involve changes in loop Burgers vector. Elastic interactions may also promote loop reactions such as absorption or coalescence or loop string formation. Loops in both W and W–5Re remained stable after annealing at 500?°C. One-dimensional hopping of loops (b?=?1/2 ?111>) was only seen in W. At the final dose (10¹⁸W⁺m^?2), a slightly denser damage microstructure was seen in W–5Re. Both materials had about 3–4?×?10¹⁵ loops m^?2. Detailed post-irradiation analyses were carried out for loops of size???4?nm. Both b?=?1/2 ?111? (～75%) and b?= ?100> (～25%) loops were present. Inside–outside contrast experiments were performed under safe orientations to determine the nature of loops. The interstitial-to-vacancy loop ratio turned out close to unity for 1/2 ?111? loops in W, and for both 1/2 ?111? and ?100? loops in W–5Re. However, interstitial loops were dominant for ?100? loops in W. Re seemed to restrict loop mobility, leading to a smaller average loop size and a higher number density in the W-Re alloy.     

High precision hyperfine structure measurements in185Re and187Re

The hyperfine structure of the atomic levels 5d ⁵ 6s ^{2 6} S _5/2 and⁴ P _5/2 in¹⁸⁵Re and¹⁸⁷Re has been studied with high precision by atomic-beam magnetic-resonance. Additional measurements were performed in the 5d ⁵ 6s ^{2 4} G _5/2 and 5d ⁶ 6s ⁶ D _9/2 states of¹⁸⁷Re. For the interpretation of the results eigenvectors in intermediate coupling have been derived by a least squares fit of all known levels of the configurations (5d+6s)⁷. The ratioB(¹⁸⁵Re)/B(¹⁸⁷Re) is the same for the⁶ S _5/2 and the⁴ P _5/2 state within the error limits of 6 parts in 10⁵. Combining the present results with the known hyperfine structure data of¹⁸⁶Re and¹⁸⁸Re we find the magnetic-dipole hyperfine anomalies for the isotopic series^185?188Re.     

Thermal desorption of N2 from (N2 + O2) coadsorbed on polycrystalline rhenium surfaces

The coadsorption of ¹⁵N₂ and O₂ on polycrystalline rhenium filament has been studied by thermal desorption mass spectroscopy. The sample was exposed to a mixture of ¹⁵N₂ and O₂ with various concentrations of ¹⁵N₂ at room temperature. It is suggested that NO on Re at low coverage is dissociative and the bonding strength of nitrogen on Re is weakened by the coadsorption with oxygen atoms.     

Electrical and structural studies of a LiBOB-based gel polymer electrolyte

A series of gel polymer electrolytes (GPEs) containing lithium bis(oxalato)borate (LiBOB), propylene carbonate (PC), and ethylene carbonate (EC) have been investigated. Poly(ethylene oxide) (PEO) was used as the polymer. First, a series of liquid electrolytes was prepared by varying the Li:O ratio and obtained the best composition giving the highest conductivity of 7.1?×?10^?3 S cm^?1 at room temperature. Then, the PEO-based GPEs were prepared by adding different amounts of LiBOB and PEO into a mixture of equal weights of EC and PC (40 % of each from the total weight). The gel electrolyte comprises of 12.5 % of LiBOB, 7.5 % of PEO, 40 % of EC, and 40 % of PC gave the highest ionic conductivity of 5.8?×?10^?3 S cm^?1 at room temperature. From the DC polarization measurements, ionic nature of the gel electrolyte was confirmed. Fourier transform infrared (FTIR) spectra of electrolytes showed the Li⁺ ion coordination with EC and PC molecules. These interactions were exhibited in the peaks corresponding to ring breathing of EC at 893 cm^?1 and ring bending of EC and symmetric ring deformation of PC at 712 and 716 cm^?1 respectively. The presence of free Li⁺ ions and ion aggregates is evident in the peaks due to the symmetric stretching of O–B–O at 985 cm^?1.     

Orion KL超水微波激射辐射的“宁静相”物理特征

利用紫金山天文台青海观测站的13.7m的射电望远镜,观测OrionKL分子云的水微波激射辐射发现这个区的微波激射活动处于”宁静”状态,峰值流量为3×10⁴Jy,大约比爆发相微波激射辐射低两个数量级宁静水微波激射处于完全饱和的辐射过程,微波激射活动区的亮温度为3×10¹³K,氢分子数密度为8×10¹⁴m^-3,微波激射辐射两能级之间的布居反转粒子数密度为5×10⁵(H₂O)m相似文献   

Pulsed plasma source of refractory metals

A pulsed plasma source of metal vapors is proposed, including refractory metals. The potentials of this source are illustrated on atomic rhenium, for example. A spectroscopic investigation of the spatial and temporal characteristics of the radiation arid the plasma parameters is conducted for a Re-He mixture. It is shown that the source permits one to realize a plasma over a wide range of parameters. In the spatial zone above the electrodes, the temporal evolution of the concentration distribution of Re atoms in the ground state is measured. A maximum value of 5·10⁺¹⁴ cm^–3 is achieved.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 48–52, April, 1988.     

Ground and γ-vibrational bands in even Os isotopes (A = 182–188) studied by (α, χnγ) and (p, χnγ) reactions

Gamma rays following ¹⁸²W(α, 2n)¹⁸⁴Os, ¹⁸⁴W(α, 2n)¹⁸⁶Os, ¹⁸⁶W(α, 2n)¹⁸⁸Os, ¹⁸⁵Re (p, 2n)¹⁸⁴Os, ¹⁸⁵Re(p, 4n)¹⁸²Os, ¹⁸⁷Re(p, 2n)¹⁸⁶Os and ¹⁸⁷Re(p, 4n)¹⁸⁴Os reactions have been measured to study the ground and γ-vibrational bands in even Os isotopes (A = 182–188). In addition to the ground-state levels the γ-vibrational bands have been identified up to the 5⁺ members. The K = 4 band head is proposed in ¹⁸⁶Os and ¹⁸⁸Os.     

The Unusual Magnetic Resonance Properties of Trigonal Prismatic Tc and Re Complexes

The electron paramagnetic resonance (EPR) spectra of the trigonal prismatic complexes Tc(abt)₃, Tc(bdt)₃, Re(abt)₃ and Re(bdt)₃ (abt, O-aminobenzenethiol; bdt, benzene-1,2-dithiol) in dilute frozen solution are interpreted in terms of an axially symmetric spin Hamiltonian, with g values close to two, principal hyperfine couplings of |A ^Tc| ~ 5–12 × 10⁻⁴ cm⁻¹, nuclear quadrupole couplings of |P ^Tc| ~ 0.3–0.35 × 10⁻⁴ cm⁻¹ and the unusual values 5 × 10⁻⁴ cm⁻¹ ~ |A _zz ^Re| < |P ^Re| ~ |A _xx ^Re| ~ |A _yy ^Re| ~ 25 × 10⁻⁴ cm⁻¹. Similar magnitudes of the parameters have been obtained by simulation of the previously published spectra of Re(pda)₃, Re(tdt)₃ and Re(pdt)₃ (pda, O-phenylenediamine; tdt, toluene-3,4-dithiol; pdt, cis-1,2-diphenylethene-1,2-dithiol) by other authors. The unexpectedly large value of P relative to A is a common feature of all the Re tris-dithiolato and related trigonal prismatic complexes studied by EPR and is attributed to the high degree of delocalization of the unpaired electron onto the ligands and the distortion of the electron charge cloud. These factors are less evident in the complexes Tc(abt)₃ and Tc(bdt)₃. Intermolecular dipolar interactions, narrowed by weak exchange, are responsible for some of the spectral features observed in the solid state and concentrated (≫1 mM) frozen solutions, although there is no evidence for specific solute–solute interactions.     

Alpha decay of neutron-deficient rhenium and osmium isotopes

Neutron-deficient osmium and rhenium isotopes were produced by bombarding an enriched¹⁴⁴Sm target with beams of²⁷Al and²⁸Si. Previously reported decay data concerning^168,169,170Os were confirmed. Three newα groups, observed in the¹⁴⁴Sm+²⁷Al reaction, were assigned to the decay of^166,167,168Re based on excitation functions,α-energy systematics and theoretical half-life predictions. Their decay properties are: $$\begin{gathered} {}^{166}\operatorname{Re} , E_\alpha = 5,372 (10) keV, T_{1/2} = 2.8 (3) s; \hfill \\ {}^{167}\operatorname{Re} , E_\alpha = 5,136 (8) keV, T_{1/2} = 6.1 (2) s and \hfill \\ {}^{168}\operatorname{Re} , E_\alpha = 4,894 (10) keV, T_{1/2} = 6.9 (8) s. \hfill \\ \end{gathered}$$ It is proposed that twoα groups, observed in the¹⁴⁴Sm+²⁸Si reaction, originate from isomeric states in^168,169Re. Our measured data for the isomeric states are: $$\begin{gathered} {}^{168m}\operatorname{Re} , E_\alpha = 5,250 (10) keV, T_{1/2} = 6.6 (15) s and \hfill \\ {}^{169m}\operatorname{Re} , E_\alpha = 5,050 (10) keV, T_{1/2} = 12.9 (11) s. \hfill \\ \end{gathered} $$      

Low-temperature nuclear orientation of173Lu,175Hf,178Ta and182m,183,184,186Re in Re

Quadrupole-interaction nuclear-orientation experiments were performed on dilute samples of the Group IIIb and IVb impurities¹⁷³Lu and¹⁷⁵Hf in a (Group VIIb) Re single crystal, the samples being preparedin situ by irradiation of a Re single crystal with 172.5 MeV alpha particles. From the γ-anisotropies at temperatures down to 8mk the quadrupole interaction frequencies Ν_Q=e²qQ/h of¹⁷³LuRe and¹⁷⁵HfRe were determined to be ?1149 (100) and ?540 (43) MHz, respectively. The negative sign in both cases indicates that the direction of the electric field gradient (EFG) at the impurity sites is fixed uniquely by the properties of the host lattice. The absolute magnitudes of these EFG's differ strongly from that of the pure system ReRe; the electronic contribution to the EFG of different impurities in Re decreases with increasing impurity valence, contrary to the expectation. As a byproduct, the quadrupole splittings of¹⁷⁸Ta,^{182m, 183, 184, 186}Re in Re were measured to be ?103(10), ?502(30), ?281(20), ?340(22) and ?73(7) MHz.