Weak e+e− lines from internal pair conversion observed in collisions of 238U with heavy nuclei

We present the results of a Doppler-shift correction to the measured e⁺e⁻–sum-energy spectra obtained from e⁺e⁻–coincidence measurements in ²³⁸U +²⁰⁶Pb and ²³⁸U +¹⁸¹Ta collisions at beam energies close to the Coulomb barrier, using an improved experimental setup at the double-Orange spectrometer of GSI. Internal-Pair-Conversion (IPC) e⁺e⁻ pairs from discrete nuclear transitions of a moving emitter have been observed following Coulomb excitation of the 1.844 MeV (E1) transition in ²⁰⁶Pb and neutron transfer to the 1.770 MeV (M1) transition in ²⁰⁷Pb. In the collision system ²³⁸U +¹⁸¹Ta, IPC transitions were observed from the Ta-like as well as from the U-like nuclei. In all systems the Doppler-shift corrected e⁺e⁻–sum-energy spectra show weak lines at the energies expected from the corresponding γ–ray spectra with cross sections being consistent with the measured excitation cross sections of the γ lines and the theoretically predicted IPC coefficients. No other than IPC e⁺e⁻–sum-energy lines were found in the measured spectra. The transfer cross sections show a strong dependence on the distance of closest approach (R_min), thus signaling also a strong dependence on the bombarding energy close to the Coulomb barrier. Received: 22 July 1997 / Revised version: 15 October 1997     

The collisional energy transfer between the D1Π and d3Π states of the NaK dimer induced by argon buffer gas

1 Π→X¹Σ⁺ transitions and the continuum spectrum of d³Π→a³Σ⁺ transitions of the NaK dimer in a heat pipe could be observed in the range of 500–700 nm. The collision-induced enhancement effects of the intensities I_d→a and the quenching effect of the intensities I_D→X by collisions with argon buffer gas at different pressures were measured experimentally. Based on the stationary collisional model and lifetime measurements, the quenching cross sections and cross sections for collision-induced energy transfer between the D¹Π and d³Π states could be estimated. Received: 13 January 1997/Revised version: 20 October 1997     

Thermal grating and broadband degenerate four-wave mixing spectroscopy of OH in high-pressure flames

2 ∑–X²Π(0,0) band of OH has been studied in premixed methane/air flames using a cw Ar⁺ laser probe. Measurements of flame temperature and pressure were derived from fits of theoretical simulations to the observed time variation of signals over a pressure range of 10 to 40 bar and for different stoichiometry that were in agreement with independent measurements using N₂ CARS and predictions of a one-dimensional flame calculation. Broadband DFWM spectra in the same band of OH were observed up to a pressure of 9 bar, above which signals were obtained only from scattering from thermal gratings. Received: 10 November 1997/Revised version: 28 May 1998     

Nonlinear response of photorefractive lithium tantalate and niobate at acoustic frequencies

An amplification of the intensity of pump oscillations is observed experimentally at frequencies from 100 Hz to 1 kHz during photoinduced light scattering and holographic-type parametric scattering in photorefractive lithium tantalate and niobate. Possible ways are analyzed for explaining the existence of a photorefractive response in these crystals over times of 10⁻²–10⁻³ s, which are five orders of magnitude shorter than the Maxwell time. Zh. éksp. Teor. Fiz. 112, 1490–1498 (October 1997)     

Prediction and Measurement of Electron Density and Collision Frequency in a Weakly Ionised Pine Fire

Pine litter flame is a weakly ionised medium. Electron-neutral collisions are a dominant form of particle interaction in the flame. Assuming flame electrons to be in thermal equilibrium with neutrals and average electron-neutral collision frequency to be much higher than the plasma frequency, the propagation of microwaves through the flame is predicted to suffer signal intensity loss. A controlled fire burner was constructed where various natural vegetation species could be used as fuel. The burner was equipped with thermocouples and used as a cavity for microwaves with a laboratory quality network analyzer to measure wave attenuation. Electron density and collision frequency were then calculated from the measured attenuation. The parameters are important for numerical prediction of electromagnetic wave propagation in wildfire environments. A controlled pine litter fire with a maximum flame temperature of 1080 K was set in the burner and microwaves (8–10.5 GHz) were caused to propagate through the flame. A microwave signal loss of 1.6–5.8 dB was measured within the frequency range. Based on the measured attenuation, electron density and electron-neutral collision frequency in pine fire were calculated to range from 0.51–1.35 × 10¹⁶ m⁻³ and 3.43–5.97 × 10¹⁰ s⁻¹ respectively.     

Baryon decay of excited states of 1P-shell hypernuclei

The baryon decays of hypernuclear resonances with the configurations s_⃛p⁻¹, p_⃛p⁻¹, and s_⃛s⁻¹ are analyzed within the framework of a translationally invariant shell model. Particular attention is paid to the influence of the nuclear structure on the decay probabilities in different channels. Joint Institute of Nuclear Research, Dubna. Institute of Nuclear Physics, Czech, Republic, Rzhezh. Institute of Nuclear Research, Russian Academy of Sciences, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 35–51, October, 1997.     

Tunable KrF laser-induced fluorescence of C2 in a sooting flame

2 in a flame, excited by a tunable KrF laser near 248 nm. The first comprises several P and R lines of the (1,0) band of the e ³Π_g-a ³Π_u Fox–Herzberg system, with fluorescence bands extending past 350 nm. The second is the band head region of the (7,1) band of the D ¹Σ_u ⁺←B^′ 1Σ_g ⁺ system, with fluorescence at 232 nm from D to the X ¹Σ_g ⁺ ground state. Neither band has been previously observed in any environment. The flame in these experiments is highly sooting, and the C₂ seen here is likely produced by laser vaporization of the soot with subsequent laser photolysis of a C₂ precursor. In a rich flame, this fluorescence could cause interferences in other studies such as KrF laser Raman scattering. Moreover, signal level calculations suggest native C₂ near 10 ppm could be readily observed using the Fox–Herzberg excitation. Raman measurements of major species (X≥0.01) in the same flame, using the KrF laser, are in good agreement with a model prediction. Received: 2 April 1998/Revised version: 8 June 1998     

Maximum spin aligned states in 98 47Ag51

New excited states have been observed in the neutron deficient isotope ⁹⁸Ag following the ⁵⁸Ni+⁵⁰Cr →¹⁰⁸Te^* heavy–ion reaction. One of these states may be interpreted as a maximum spin aligned state of the πg_9/2 ⁻³νg_7/2 configuration. Other possible interpretations within the nuclear shell model are discussed as well. Received: 24 October 1997     

Tomographic reconstruction of the OH*-chemiluminescence distribution in premixed and diffusion flames

A fast tomographic reconstruction device has been developed to detect the two-dimensional distribution of the chemiluminescence of OH^* in the reaction zones of flames. In the set-up, special emphasis was placed on the applicability of the technique to turbulent flames. A spatial resolution of the system, <1–2 mm, and an exposure time of 100–200 μs are required to resolve the chemiluminescence signal of OH^* originating from the folded flame front of a turbulent flame.     

Dynamics of erosion plasma formation and formation of a plasma flame with a condensed disperse phase when quasi-continuous laser radiation acts on bismuth

The dynamics of near-surface plasma formation and the formation of an erosion plasma flame was investigated for quasi-continuous laser radiation (λ=1.06 μm, q=0.1–10 MW/cm², τ∼1.5 msec) acting on bismuth targets in air. The absence of low-threshold plasma formation at q<2 MW/cm² was established and explained. Instabilities in the plasma formation were revealed and the range of laser radiation power densities (2≤q≤4 MW/cm²) at which these instabilities take place was determined. At q≥5.4 MW/cm², brightening of the flame was noted. The dependence of the luminescence temperature of the flame on the laser radiation power density q was determined. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 126–133, January–February, 1998.     

Dielectric breakdown of rubber materials by femtosecond irradiation

We report the reversible micro-structuring of a synthetic rubber polymer (cis1,4-polybutadiene (PB)) by femtosecond laser illumination. Visco-elastic relaxation of the optically damaged region was observed. The recovery time, typically 10²–10⁴ ms, can be varied by changing the irradiation pulse energy. Multi-shot-induced damage recovers on the much longer scale of 10¹–10² s. It was found that the doping of PB by 4 wt. % of pentazadiene ([4-NO₂]–phenyl–N=N–N(C₃H₇)–N=N–phenyl–[4-NO₂]) reduces the threshold of light-induced photo-modification by 20%. This is explained by photo-induced (homolytic) cleavage of the pentazadiene bonds and formation of gaseous N₂, which facilitates material failure at the irradiated spot. The recovery of optical transmission can be applied to optical memory, optical and micro-mechanical applications. The underlying mechanism of the phenomenon is discussed in terms of anelastic α- and β-relaxation (polymer backbone and chains/coils relaxation, respectively). Received: 11 October 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +81-88/656-7598, E-mail: misawa@eco.tokushima-u.ac.jp     

Infrared absorption spectra and structure of TiO2-SiO2 composites

The composites xTiO₂-(1−x)SiO₂ (x = 0.1, 0.5, 0.9) were obtained by coprecipitation from solutions of alkoxides: tetraethoxysilane (TEOS) and titanium tetraisopropoxide (TIPT). Intermolecular interaction of the components of the composite is apparent in the IR absorption spectra in the 928–952 cm⁻¹ region, and is connected with bending vibrations of the Si-O-Ti bond. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 724–728, September–October, 2008.     

Energy transfer in the A2Σ+ state of OH following v’ = 1 excitation in a low pressure CH4/O2-flame

2 Σ⁺(v’=1) level of OH. Measurements were performed in a laminar premixed flame at 10 Torr total pressure. The low pressure allowed the spatial variation of the effective quenching rate to be determined through the flame front. In addition, the dependence of the quenching rate on rotational quantum number was measured by exciting a series of rotational lines in the range N’=0–16. The results show that the total quenching rate decreases only 17% through the flame front, in the region where OH can be detected. Nevertheless, the absolute value of the quenching rate Q is required if absolute concentrations are to be determined from LIF-signals. The variation both of Q and of the rotational relaxation rate with excited rotational quantum state must be known for quantification of LIF-temperature measurements via the Boltzmann relation. Finally, the rotational and vibrational energy transfer (RET, VET), was investigated by recording the spectrally and temporally resolved fluorescence. For all excited rotational lines, efficient RET to neighbouring rotational states was observed, but only very little VET. Total RET rates were determined from the difference between the time-resolved broadband (total fluorescence) and narrowband (fluorescence from the laser excited level) curves. The experimental results were compared with simulations using a dynamic model, which describes the energy transfer for flame conditions. With the available input data (temperature, major species concentrations and collision-partner specific RET cross sections), good agreement was obtained. Received: 3 February 1997/Revised version: 3 September 1997     

Effect of a low-frequency magnetic field on the structure of globular blood proteins

We used IR Fourier absorption spectra of blood to study changes in the structure of globular blood proteins with extracorporeal autohemomagnetotherapy, used to treat ischemic heart disease. We compare the spectra of blood before and after magnetotherapy in the regions: amide I (1655 cm⁻¹), amide II (1545 cm⁻¹), amide III (1230–1350 cm⁻¹), amide IV and amide V (400–700 cm⁻¹). We have shown that pronounced changes in the spectra in the indicated regions on direct exposure of blood in vivo to a low-frequency pulsed magnetic field are connected with conformational changes in the secondary structure of globular blood proteins, which are apparent in the increase in the contribution of the α-helix conformation. We discuss the magnetotherapy-initiated appearance of new IR absorption bands at 1018 and 1038 cm⁻¹ and an increase in the intensity of a number of other bands located in the 1000–1200 cm⁻¹ region, which suggests a change in the concentration of some blood components. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 665–669, September–October, 2007.     

Characteristics of thermally stimulated depolarization phenomena in zinc-oxide ceramics for varistors

The results of experimental investigations and an analysis of the temperature dependences of the thermally stimulated depolarization current are presented for zinc-oxide ceramics suitable for use in high-voltage varistors. A model for the depolarization phenomena is proposed that takes into account charge exchange on localized electronic states on both sides of the intercrystallite potential barrier. The model is used to obtain estimates of the ionization energy and density of shallow (∼0.07 eV, 1×10¹⁷ cm⁻³) and deeper (∼0.2 eV, 1×10¹⁸ cm⁻³) bulk levels and surface-localized levels (∼0.1 eV, 1×10¹³ cm⁻²). Zh. Tekh. Fiz. 67, 60–63 (October 1997)     

Conditions for XUV amplification considering recombination in clusters

3 cm^-l for a wavelength of λ_R≈200 Å in a time ≲1 ps can be expected. The measurable gain G_real depends on the cluster density N_cl. For N_cl≈10¹⁶ cm^-3 we expect G_real≳20 cm^-1. Received: 30 October 1997     

Production, isolation, and characterization of group-2 metal-containing endohedral metallofullerenes

80 , Ca/Sr/Ba@C₈₂, Ca/Sr/Ba@C₈₄) are investigated for the first time by UV-Vis-NIR absorption spectroscopy and high-resolution ¹³C NMR. Direct evidence of the endohedral nature and cage structures are revealed by these measurements. Furthermore, we have found that each metallofullerene has 2–4 structural isomers, which have been isolated by multistage high-performance liquid chromatography. These isomers have different cage structures and give characteristic UV-Vis-NIR absorption spectra. Received: 22 September 1997/Accepted: 16 October 1997     

Conversion--electron gamma--ray coincidence spectroscopy of superdeformed 135Nd

Three mini-orange conversion–electron spectrometers and four Euroball Ge Cluster detectors have been used for γ–e^- coincidence spectroscopy of superdeformed ¹³⁵Nd. Transitions within the superdeformed band are shown to have the expected E2 multipolarity. The 766.5–keV transition which links the band to a positive-parity state has a conversion coefficient consistent with M1 multipolarity. Consequently, positive parity is deduced for the superdeformed band. No evidence for E0 transitions was found. Received: 22 December 1997 / Revised version: 19 January 1998     

Characterization of a Br(2P1/2)–CO2(1001-1000) transfer laser driven by photolysis of iodine monobromide

2 laser operating on the 10⁰1-10⁰0 transition at λ=4.3 μm and pumped by E –V energy transfer from Br(²P_1/2) has been demonstrated. The dynamics and performance of this device were characterized by observing the time-resolved stimulated emission and the steady-state spontaneous side fluorescence after photolysis of IBr or Br₂ by a frequency-doubled Nd:YAG laser or Ar⁺ laser, respectively. Although the E –V excitation kinetics are favorable, rapid vibrational relaxation limits laser action to CO₂ pressures of less than 1 Torr. Numerical modeling of laser pulse shapes and the dependence on IBr and CO₂ pressure and photolysis energy establish a relatively high gain of 0.33%/cm, a CO₂-pressure-dependent optical loss of 0.04–0.06%/cm, and an efficiency of 2×10^-5 4.3-μm-laser photons per incident photolysis photon. The CO₂ fluorescence after photolysis of a fixed Br₂/CO₂ gas mixture decreases as a function of photolysis time by about 30%/h, indicating the photolytic production of an important quencher. Received: 23 June 1997/Revised version: 23 September 1997     

High spin states and evidence for octupole correlations in 117Xe

High-spin states of ¹¹⁷Xe were investigated by means of in-beam γ-ray spectroscopic techniques via the reaction of ²⁸Si bombarding a ⁹²Mo target at beam energies of 100-120 MeV. A positive-parity rotational band decaying into the yrast negative-parity band by a series of enhanced E1 transitions was observed for the first time, implying the existence of octupole correlations in ¹¹⁷Xe. The B(E1) values increase with spin. The νd_5/2 band was firmly established up to 27/2⁺ and the B(M1)/B(E2) ratios were extracted from the relative intensities of γ-rays in this band. The previously known νh_11/2 and νg_7/2 [413]5/2⁺α=−1/2 bands were confirmed and extended up to high spins and two bandcrossings are observed in the latter at ħω=0.33 and 0.44 MeV, respectively. The bandcrossings and configurations of these bands are discussed by TRS and CSM calculations. In a γ–γ–t measurement, the 11/2⁻ and 7/2⁻ levels were identified as two isomers with half-lives of 59.4±20 ns and 16.5±8.0 ns, respectively. Received: 17 June 1997 / Revised version: 29 September 1997