Relaxation of the conductivity of CsI-Tl after excitation by subnanosecond electron pulses

The pulsed conductivity is investigated for a CsI-Tl crystal having a Tl⁺ concentration N=8×10¹⁷cm⁻³ and excited by an electron beam (0.2 MeV, 50 ps, 10²–10⁴ A/cm ²). It is shown that the amplitude of the conduction current pulse is almost an order of magnitude lower than for “pure” CsI crystals irradiated under like conditions. The conduction current relaxation time is preserved up to τ=100 ps in this case. Under the experimental conditions, therefore, the lifetime of electrons in the conduction band is controlled by trapping at Tl⁺ centers. The electron capture cross section at a Tl⁺ center is determined: σ=7×10⁻¹⁶ cm², which agrees in order of magnitude with estimates of the capture cross section for a neutral trapping center. Fiz. Tverd. Tela (St. Petersburg) 40, 66–67 (January 1998)     

Structural features of aluminium alloy 1441 irradiated by Ar+ ions

Using electron microscopy it was found that irradiation of clad cold-worked specimens made of commercial aluminium-lithium alloy 1441 by the Ar ⁺ ions of energy 40 keV at low doses of irradiation (10¹⁵ cm⁻², irradiation time 1 s, T < 70 °C) and ion-current density of about 100 μA/cm² results in the transformation of the cellular structure formed in the alloy under deformation. As the dose of irradiation is increased up to 10¹⁶ cm⁻², a transition from a cellular to a subgrain structure close to a polygonal one is observed. The efficiency of the process is increased with ion-current density. Furthermore, under ion irradiation at increased ion-current densities, the β′(Al ₃ Zr) and Al ₈ Fe ₂ Si particles present in the deformed alloy dissolve, and disperse particles of a new Al ₂ LiMg phase of platelet shape are formed. The changes in the dislocation structure and phase composition in alloy 1441 are observed several seconds after irradiation not only in the surface layer adjacent to the ion incorporation band but also through the thickness of the specimen tens of thousands times greater than ion projective ranges. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–81, February, 2007.     

Wear resistance of the ion-modified surface of zirconium-alloy tubes irradiated by He+ and Ar+ ion beams with wide energy spectra

The results of investigating the wear resistance of E110 alloy samples irradiated by a He⁺ + Ar⁺ beam with a wide energy spectrum are presented. Surface modification under irradiation by an Ar⁺ beam at doses higher than 2 × 10¹⁸ ion/cm² is shown to cause substantial enhancement of the wear resistance of samples because the structural homogeneity of near surface layers increases, the surface roughness decreases, and its microhardness increases. The application of a mechanical-geometrical wear model based on the experimental wear characteristics determined during accelerated tests indicates that the thinning of an alloy cladding can reach rates of 10⁻⁶–10⁻³ mm/s, which agree satisfactorily with data obtained in other simulation experiments. The presence of an oxide film changes a wear process characterized by an abrasive component.     

One-dimensional ionic conduction in solid Ag2 Tl6I10

The ionic and electronic conductivities of Ag₂Tl₆I₁₀ single crystals have been studied as a function of crystallographic orientation and temperature from 20 to 135°C. EMF as well as AC and DC techniques have been employed. The highly anisotropic material is predominantly an Ag⁺-ion conductor parallel toc-direction, with the Ag⁺ ions moving through linear channels that are not interconnected. The conductivity σ_‖c =1.6×10⁻⁷Ω⁻¹cm⁻¹ at 25°C, with an activation enthalpy for σ_‖c of 0.38 eV. The conduction perpendicular toc-direction has been found to be predominantly electronic with a value of σ_⊥c =3×10⁻⁹Ω⁻¹cm⁻¹ at 25°C and an activation enthalpy for σ_⊥c of 0.64 eV. This is the first observation of one-dimensional Ag⁺ conduction and this type of orientation-dependent change from ionic to electronic conduction. On leave from Institute of Physics, Academia Sinica, Peking, China.     

ESR of V4+ in α-RbTiOPO4 single crystals

We have recorded and investigated the ESR spectrum of vanadium-doped α-RbTiOPO₄ single crystals in the temperature interval 77–300 K. Two types of structurally distinct centers, V1 and V2, with a 4:1 ratio of the peak intensities were observed. The angular dependences of the resonance magnetic fields are described by a spin Hamiltonian corresponding to axial symmetry with the parameters g _∥1=1.9305, g _⊥1=1.9565, A _∥1=−168.2×10⁻⁴cm⁻¹, and A _⊥1=−54.3×10⁻⁴cm⁻¹ for V1 centers and g _∥2=1.9340, g _⊥2=1.9523, A _∥2=−169.0×10⁻⁴cm⁻¹, and A _⊥2=−55.2×10⁻⁴cm⁻¹ for V2 centers. A model of a paramagnetic center is proposed: The vanadium ions replace titanium ions in two structurally distinct positions Ti1 and Ti2 (V1 and V2 centers, respectively). The possibility that a VO²⁺ ion forms when α-RbTiOPO₄ crystals and crystals of the KTP group (KTiOPO₄, NaTiOPO₄, α-and β-LiTiOPO₄), studied earlier, are doped with vanadium is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 534–536 (March 1998)     

Polarized absorption spectra of Co2+ in Na2Cd3Cl8 single crystals

Summary The polarized optical absorption spectra of Na₂Cd₃Cl₈: Co²⁺ in the range of 15 000 to 40 000 cm⁻¹ down to 15 K are reported. The Co²⁺ ion is found to occupy the Cd²⁺ sites in octahedral geometry and the spectra are interpreted satisfactorily in terms of a cubic ligand field model including spin-orbit coupling. The observed crystal field spectra are well reproduced withB=745 cm⁻¹,C=3410 cm⁻¹,Dq=700 cm⁻¹ and ζ (spin-orbit interaction) =520 cm⁻¹. No spectral evidence for tetragonal distortion is observed.     

Modification of nanostructured states in ion-implanted platinum

The formation of nanostructures in subsurface volumes of Pt as a result of the implantation of Ar⁺ ions (E = 30 keV, F = 10¹⁶−10¹⁸ cm⁻²) was studied by the method of field ion microscopy. This phenomenon was observed at distances not less than 60 nm from the irradiated surface of the metal (at F = 10¹⁸ cm⁻²). It was established that the optimum regime for obtaining nanocrystalline structures in subsurface volumes of ion-implanted platinum is irradiation to F = 10¹⁷ cm⁻² (E = 30 keV, j = 200 μA cm⁻²). In such a regime, the formation of nanoblock structures is observed at distances not less than 20 nm from the irradiated surface, rather than the formation of vacancy pores.     

The characteristics of high current amorphous silicon diodes

Amorphous siliconp−n junctions with various doping profiles have been prepared by the glow discharge technique and the effect of the barrier profile on electrical properties investigated. Current densities of up to 40 A cm⁻² with rectification ratios of 10⁴–10⁵ were obtained withn ⁺−ν−p ⁺ structures. The diode quality factor has also been investigated, both in the dark and under illumination.     

ESR study of exchange coupled pairs in copper diethyldithiocarbamate

ESR investigations on exchange coupled pairs of Cu ions in single crystals of Cu(dtc)₂, isomorphously diluted with the corresponding diamagnetic zinc salt, are reported. The spin Hamiltonian parameters for the coupled species (S=1) are:g _‖=2.1025,g ₊=2.031,A=75.1×10⁻⁴ cm⁻¹,B=14.8×10⁻⁴,D=276.0×10⁻⁴ cm⁻¹ andE=46.7×10⁻⁴ cm⁻¹. While theg andA tensors show tetragonal symmetry, the zeor-field splitting tensor is rhombic and has principal axes different from those of theg andA tensors. Intensity measurements made down to 4.2 K indicate that the exchange is ferromagnetic with |FFF| ∼ 10 cm⁻¹. Direct dipole-dipole interaction appears to be the major contribution to the zero-field splitting. A calculation on the distributed point dipole model shows that dipolar interaction is considerably modified by the high covalency of the Cu-S bond and accounts for the rhombic nature of the tensor. The possible exchange mechanisms in Cu(dtc)₂—direct exchange and superexchange through the bridging sulphurs—are discussed.     

Raman-gain, linewidth, and effective g -value with spin-flip-Raman scattering in inSb

In this paper we report on measurements of spin-flip-Raman gain inn-InSb as a function of the magnetic field. The measurements were carried out at temperatures of 1.8 K and 4.2 K and at a carrier concentration of 1.35×10¹⁵ cm⁻³. The Raman cross sections obtained from these results, e.g. 1.25×10⁻²⁰ cm²/sr at a magnetic field of 10 kG and a pump frequency of 1884.35 cm⁻¹, agree very well with those theoretically predicted by Wherrett and Wolland. Furthermore, these measurements yield line shapes and linewidths of the spontaneous scattering (100–1500 MHz) and allow the determination of the effectiveg-value with an accuracy known from ESR-investigations. These results are discussed in terms of already published theoretical investigations.     

Update of the e + e − → π+π− cross section measured by the spherical neutral detector in the energy region 400 < √s < 1000 MeV

The corrected cross section of the e ⁺ e ⁻ → π⁺π⁻ process measured in the spherical neutral detector experiment at the VEPP-2M e ⁺ e ⁻ collider is presented. The update is necessary due to a flaw in the e ⁺ e ⁻ → π⁺π⁻ and e ⁺ e ⁻ → μ⁺μ⁻ Monte Carlo event generators used previously in data analysis. The text was submitted by the authors in English.     

Spectroscopic properties of Nd<Superscript>3+</Superscript>:CaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> crystal

The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd³⁺ ions in CaNb₂O₆ crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10⁻²⁰ cm² with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd³⁺ ions in CaNb₂O₆ crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω _t are Ω ₂=5.321×10⁻²⁰ cm²,Ω ₄=1.734×10⁻²⁰ cm²,Ω ₆=2.889×10⁻²⁰ cm². The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β ₁=36.03%,β ₂=52.29%,β ₃=11.15%,β ₄=0.533%. The emission cross section at 1062 nm is 9.87×10⁻²⁰ cm².     

Laser photoacoustic spectroscopy of iodine molecule: Single and two-photon absorption

Photoacoustic spectroscopy of iodine molecule has been studied in gas phase using nitrogen laser-pumped tunable dye laser. The experiment yielded the vibrational spectrum corresponding toX ¹Σ⁺(0 _g ⁺ )→B ³Π(0 _g ⁺ ) transition up to the convergence limit. The photo-acoustic spectrum in the region 17580–18850 cm⁻¹ is presented along with the vibrational analysis. Five of the vibrational bands reported earlier by Venkateswarlu, Kumar and McGlynn have been partially resolved and the structure of one of them has been analyzed and shown to be due to an overlap of (14, 2) and (12, 1) bands. The analysis was based on a comparison with the highly resolved spectrum of Gerstenkorn and Luc. The structure observed in the region 20200–20750 cm⁻¹ which is beyond the convergence limit of the transitionX ¹Σ⁺(0 _g ⁺ )→B ³Π(0 _u ⁺ ) has been analyzed as due to two-photon absorption. Most of the bands could be assigned to two transitions both originating in the ground state and terminating in two different electronic states 1 _g andE(0 _g ⁺ ), atT _e=40821 cm⁻¹ (orT ₀=41355 cm⁻¹) andT _e=41411 cm⁻¹ (orT ₀=41355 cm⁻¹) respectively.     

Addition and spin exchange rate constants by longitudinal field μSR: The Mu+NO reaction

The addition reaction Mu+NO+M→MuNO+M and the spin exchange reaction Mu(↑) +MO(↓)→Mu(↓)+NO(↑) have been measured by longitudinal field μSR at room temperature in the presence of up to 58 atm of N₂ as inert collider. The pressure dependence of the longitudinal relaxation rate due to the addition reaction (λ_c) demostrates that the system is still in the low pressure regime in this pressure range. The corresponding termolecular rate constant has been determined ask _0,Mu =(1.10±0.25)×10⁻³² cm⁶ molecules⁻² s⁻¹, almost 4 times smaller than the corresponding H atom reactionk _0,H=3.90×10⁻³² cm⁶ molecules⁻² s⁻¹ [I.M. Campbell et al., J. Chem. Soc. Faraday Trans. 1.71 (1975) 2097]. The average value of the spin exchange rate constants in the 2.5–58 atm pressure range,k _SE=(3.16±0.06)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, is in good agreement with previous values obtained by transverse field μSR [D.G. Fleming et al., J. Chem. Phys. 73 (1980) 2751].     

Raman scattering in a near-surface n-GaAs layer implanted with boron ions

Structure in the Raman scattering spectra of near-surface n-GaAs layers (n=2×10¹⁸ cm⁻³) implanted with 100 keV B⁺ ions in the dose range 3.1×10¹¹–1.2×10¹⁴ cm⁻² is investigated. The qualitative and quantitative data on the carrier density and mobility and on the degree of amorphization of the crystal lattice and the parameters of the nanocrystalline phase as a result of ion implantation are obtained using a method proposed for analyzing room-temperature Raman spectra. Fiz. Tverd. Tela (St. Petersburg) 41, 1495–1498 (August 1999)     

Secondary-ion emission of amino acids

Secondary-ion mass spectroscopy (SIMS) is a hydrogen, isotope and compound sensitive analytical technique of extremely high absolute sensitivity. Continuing earlier measurements for carboxylic acids, adsorbed alcohols etc., we have carried out a systematical investigation of secondary-ion emission from metal-supported amino acids, containing various functional groups (e.g., alanine, phenylalanine, cysteine, arginine). In order to avoid damage effects we applied extremely small primary-ion current densities in the 10⁻⁹ A·cm⁻² range. The main results of our investigations can be summarized as follows:

Antikaon angular distributions in the reaction γd → K −Θ+ p → K − K + np near the threshold and the parity of the Θ+ Pentaquark

Within the spectator model, we study the reaction γd → K ⁻Θ⁺ p → K ⁻ K ⁺ np in the threshold energy region. We present the predictions for the exclusive and inclusive K ⁻-meson angular distributions in the laboratory system for this reaction calculated for two possible parity states of the Θ⁺ resonance at 1.5-and 1.75-GeV beam energies with and without imposing the relevant kinematical cuts on those parts of the sampled phase space where the contribution from the main background sources, associated with the ϕ(1020), Λ(1520) production as well as with the K ⁻ p rescattering in the final state, is expected to be dominant. We show that, under the chosen kinematics, these distributions are sensitive to the Θ⁺ parity and, therefore, can be used as a filter for the determination of its parity. The text was submitted by the author in English.     

Negative parity states in144Nd and multipolarity of gamma-transitions from 1− to 2+ states by beta-gamma-gamma angular correlation method

Some of the low-lying states in many isotopes¹⁴⁴Nd,¹⁴⁸Sm,¹⁵²Gd and¹⁵⁶Gd show a similar typical behaviour. The first 2⁺ is regarded as a single quadrupole phonon state and 3⁻ as a single octupole phonon state. The levels with the spins and parities 1⁻, 5⁻, 3⁻, 4⁻, etc. are considered due to the simultaneous excitation of quadrupole and octupole phonons. If this consideration is correct, then the transition fromJ ⁻ to 2⁺ states must contain an appreciableE3 content. Theβ-γ-γ angular correlation coefficients for the cascade ofβ-rays ofE _max 800 keV→γ-rays of 1489 keV→γ-rays of 696 keV are used to estimateE3 content inE1 transition in¹⁴⁴Nd.     

The true potential energy curves for different states of SiO and SiS molecules

The true potential energy curves forX ¹ Σ ⁺, a³ π _r,A ¹ π,e ³ Σ ⁻,E ¹ Σ ⁺,c ³ π _i states of astrophysically important molecule SiO, whose spectra were observed in the sunspots, have been constructed using the method of Lakshman and Rao. Dissociation energy and ionization potential have been estimated as 65,350 cm⁻¹ and 92,854 cm⁻¹ respectively and found to be in good agreement with the values cited in literature. The true potential energy curves forX ¹ Σ ⁺,D ¹ π andE ¹ Σ ⁺ states of SiS molecule have been constructed by the same method and its dissociation energy in the ground state has been estimated using Hulburt-Hirschfelder potential function as 54,765 cm⁻¹ in good agreement with 53,250.9 cm⁻¹ given by Herzberg.     

Field dependence of spin-lattice relaxation of Nd3+ ions in Y3Al5O12 crystals

Our studies involve measuring spin-lattice relaxation times for Nd³⁺ ions in yttrium-aluminum garnets over the temperature range 4–50 K at 9.25 and 36.4 GHz for different orientations of the external magnetic field in relation to the crystallographic axes. The temperature dependence of the relaxation rate is described by T ₁ ⁻¹ =AT ⁿ+b exp(−Δ/kT), where n varies from sample to sample, with n=1 for “perfect” samples (i.e., with the longest relaxation times). Here Δ is approximately 130 cm⁻¹, which is the energy of the excited Kramers doublet of the neodymium ion closest to the ground state, and this makes it possible to interpret the second term in T ₁ ⁻¹ as the contribution of two-stage relaxation proceeding through the intermediate level Δ. A strong field dependence of these processes has been discovered: when the frequency was increased fourfold, the relaxation rate increased by a factor of 10. The effect is a specific manifestation of the degeneracy of the excited level, breaking of the symmetry of the crystalline field due to lattice defects, and the prevalence of deformations of a certain type in the spin-lattice interaction. Zh. éksp. Teor. Fiz. 111, 332–343 (January 1997)