Dependence of the stopping power of charged particles on the physical state of organic dielectric compounds

The effect of induced crystallinity by preirradiation annealing on range energy relationships have been investigated for a number of energetic ions and Cf-252 fission fragments in polymer dielectric nuclear track detectors DNTDs. The stopping power of the defferent polymeric detectors (cellulose based derivatives), have been examined in the solid (amorphous and crystalline) phases. X-ray diffraction of annealed CA80-15 (made by Kodak Pathe' France) and other polymers show a general decrease in (dE/dX) and hence variations of electron density distribution, leading to increased penetration ranges for charged particles in DNTDs.     

Dependence of the spontaneous emission of singlet oxygen on the refractive index and molecular polarizability of the surrounding dielectric media

The rate constants (k _r ) for singlet oxygen O₂ (a ¹Δ _g ) luminescence in several selected solvents and in binary solvent mixture (acetone-toluene) were measured. All data have been normalized such that k _r ^rel = 1.0 in toluene. It has been demonstrated that the changes in these rate constants were caused both by optical properties of a medium (the local field factor and density of photon states) and by an inherent property of the emitter of ¹O₂ (the square of transition moment). In its turn, the value of the transition moment is directly proportional to molecular polarizability of the medium molecules.     

Experimental lifetimes of some levels of KrI

Lifetime of nine levels belonging to the and configuration of neutral krypton have been measured by high-frequency deflection technique with a delayed coincidence single photon counting arrangement. The results have been compared with other experimental and theoretical values. The lifetimes of the 9s[3/2]₁ and 7p[1/2]₀ levels have been measured for the first time.     

Radiative lifetimes of some states of NeII

The radiative lifetimes of eight states of NeII, namely 3d, 3d′, 4s and 4s′, are measured. The delay-coincidence method with pulsed electron excitation is employed. A comparison with other results is also reported.     

Radiative lifetimes of some excited CoI states

The lifetimes of atomic CoI states have been determined using the delayed coincidence technique. A tunable dye laser pumped by a nitrogen laser was employed for the excitation of cobalt atoms in an atomic beam. The lifetimes were derived from the time dependent fluorescence intensity of the observed lines after the excitation. For the measurement of the lifetimes of thee ⁴ F _9/2,f ⁴ F ^9/2 andf ⁴ F _7/2 levels a two step excitation was applied. In case of overlapping measurement we find our results to be in good agreement with those reported by Becker [1].     

Pressure dependence of positron lifetimes in V3Si

We have measured positron lifetimes in V₃Si at hydrostatic pressures of 0 to 20 kb, at room temperature. The lifetimes were independent of pressure, within the experimental uncertainty of ± 2 ps; the results of eight measurements all were between 129 and 133 ps.     

Pressure dependence of dielectric constants of alums

The effect of hydrostatic pressure p on the low frequency dielectric constant ? has been investigated for 31 alums of different composition at 293 K in the pressure range between 0 and 7 kbar. The ?(p)-curves deviate from linearity. For almost all alums with symmetric ions the first-, second-, and third-order pressure derivatives of the dielectric constant obey the following relations:

$\text{(}\text{??}\text{?p}\text{)}{}_{\mathrm{T}}\text{< 0, (}\text{?}{}^2\text{?}\text{?p}{}^2\text{)}{}_{\mathrm{T}}\text{> 0, and (}\text{?}{}^3\text{?}\text{?p}{}^3\text{)}{}_{\mathrm{T}}\text{< 0}$

. The logarithmic volume derivative of the low frequency polarizability, $\text{(}\text{? ln α}\text{? ln V}\text{)}{}_{\mathrm{T}}$, is found to be quasi-invariant also in the isotypic crystal group of alums (Jarman's rule). For the cases, where piezooptical data are available, the optical and infrared contributions to the volume dependence of the polarizability are determined.     

The influence of several parameters on the lifetimes and intensities of positron lifetime spectra of metals

The influence of the instrumental time-resolution function and the source-surface spectrum on the lifetimes and intensities of positron lifetime spectra is studied by a computer simulation of such spectra. The prompt curve is described not by a sum of Gaussian curves but by the convolution of a Gaussian curve with a double-sided exponential. It is shown that the fitted lifetimes and intensities considerably depend on these parameters.     

Dependence of dielectric permittivity of moist disperse materials on the temperature

The behavior of the dielectric permittivity of a mixture of disperse materials with change in volume content of the component with high dielectric permittivity (water) and temperature is investigated. An analysis of the results is presented. A formula is given for the calculation of the dielectric permittivity of moist disperse materials as a function of the temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 65–68, January, 1982.     

Dependence of lattice constants and bulk moduli on pseudopotential properties

Using a nearly-free-electron model and model pseudopotentials, an analytical relation between the Wigner-Seitz radius for a metal, r_ws, and the core radius of the model pseudopotential, r_c is derived. In addition, a semi-empirical formula for the bulk moduli is obtained.     

Square-well models and mismatches of dielectric constants and lattice constants of heterostructures

The reliability of using the square well approximation model to describe the energy band profile of heterostructures is discussed. The effects of dielectric constant mismatch for type I and type II heterostructures and the lattice constant mismatch for the strained-layer heterostructures are studied.     

Fluorescence lifetimes and radiative rate constants of alkanes at 25°C

Fluorescence lifetimes of 33 alkanes were measured at 25°C using a 0.7 ns pulse radiolysis system and the relationship between molecular structure, fluorescence lifetime (τ), quantum yield (Φ_f) and radiative rate constant (R = $\text{Φ}{}_{\mathrm{f}}\text{τ}$) is discussed. The τ's showed a large dependence on the molecular structure, however, the R-values were approximately constant for groups of alkanes: R = 1.3×10⁶s^?1 for n-alkanes, R ≈ 4×10⁶ s^?1 for aliphatic vicinally substituted dimethyl alkanes, R = 7×10⁶s^-1 for cyclohexane and alkylcyclohexanes, and R = 10×10⁶s^?1 for di- and trimethylcyclohexanes. The excited state lifetimes of some non-fluorescing alkanes were also determined from steady-state photolytic quenching data and found to be very low (? 0.3 ns).     

Dependence of electron and positron backscattering coefficients on Al film thickness

The backscattering coefficient of 1-4 keV electron and positron beams normally incident impinging on Al thin film targets is stochastically modeled within a Monte Carlo frame work. The aim of the present paper is to study the behavior of the backscattering coefficient as a function of the Al film thickness. To the authors’ knowledge, no theoretical or experimental work on the dependence of the positron backscattering coefficient on film thickness targets has been reported so far. It is found that the backscattering coefficient for both electron and positron beams presents different behaviors when the Al film thickness belongs to the nano-scale. Beyond this scale, the behavior becomes qualitatively similar.     

Prediction of complex dielectric constants of polymer-clay nanocomposites

In this Letter, simple theoretical models are presented to predict the influence of aspect ratio, orientation, distribution, and interphase of layered silicates on the dielectric properties of polymer-clay nanocomposites. The predictions are in good agreement with experimental data. The results show that the morphology of the clay fillers and the thickness and dielectric properties of the interphases play an important role in determining the dielectric properties of polymer-clay nanocomposites.     

Radiative lifetimes of some excited states of neutral xenon

The radiative lifetimes of ten levels belonging to the nf (n=4-7) and three levels belonging to the ns (n=8,9) configuration of XeI have been measured using the high frequency deflection technique together with a delayed coincidence single-photon counting arrangement. Lifetimes of some of the levels have been measured for the first time. The results have been compared with other experimental and theoretical values.     

Radiative lifetimes of some excited levels in Eu II

Radiative lifetimes of the six levels 6p _3/2(7/2, 3/2)_{2, 3, 4, 5} and 6p _1/2(7/2, 1/2)_{3, 4} in Eu II are measured with a laser-ion beam technique using intracavity excitation and tandem pumping.     

Modeling the electrical characteristics of periodic dielectric media

The dispersion of the effective permittivities of two inhomogeneous matrix systems with unidirectional fiber inclusions with a square cross section is studied. Interpolation formulas for the effective permittivity as a function of the frequency are obtained, whose range of applicability is determined through physical modeling and comparison with known systems of equations admitting exact solutions. It is established that the effective loss factor exhibits anomalous behavior in the vicinity of the critical concentration of inclusions.