Phosphates of Ca8ZnLn(PO4)7 (Ln3+ = La – Nd, Sm – Lu) with β-Ca3(PO4)2-type structure were prepared by high-temperature solid-state technique on air. All compounds of Ca8ZnLn(PO4)7 are ...centrosymmetric and have R3¯c space group, which has been proved by several methods such as second-harmonic generation, dielectric spectroscopy, and Rietveld analysis. The influence of Ln3+ on the structure, luminescent properties and temperature of phase transitions, which corresponds with “tetrad” effect, has been investigated. The bandgap width and location of 4f Ln3+ and Ln2+ levels relatively to the energy bands were determined using the data of luminescent spectroscopy.
•Space group of Ca8ZnLn(PO4)7 compounds as centrosymmetric R3¯c and Zn2+ ions occupy only M5 position according to SXRD refinement.•The distribution of Ln3+ between M1 and М3 positions depends on the ionic radius of Ln3+.•Temperatures of first-order reversible phase transitions correspond with the “tetrad” effect.•The energies of excitons creation and bandgap were determined as Eex = 7.94 eV and Eg = 8.57 eV, respectively.•A scheme, which determines the location of Ln3+ and Ln2+ 4 f and 5d levels relatively to the energy bands was developed.
The luminescent properties of Y
1 –
x
Sc
x
PO
4
: 0.5 mol % Eu
3+
(
x
= 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) solid solutions are studied at the excitation by the radiations of ultraviolet and ...vacuum-ultraviolet ranges. The disordering of the solid-solution crystal structure is shown to influence the structure of the Eu
3+
luminescence spectra. The bandgap width is shown to nonlinearly depend on the solid solution composition. The model explaining this effect is proposed.
We studied optically induced effects in ultrafine Al
2
O
3
–BeO ceramics irradiated with a high-dose pulsed electron beam (130 keV). Upon optical excitation of ceramics at 470 nm, optically ...stimulated luminescence is observed due to the depletion of traps associated with thermoluminescence peaks at 380 and 530 K. These traps are characterized by a complex energy spectrum with a nonuniformly distributed photoionization cross section. The prospects of using optically stimulated luminescence of Al
2
O
3
–BeO ceramics in high-dose dosimetry (3–30 kGy) have been proved.
Abstract
The work addresses the use of electron beam produced by the
linear induction accelerator to generate terahertz radiation pulses
of 100 MW power level based on a free electron laser scheme. ...The
beam parameters required for efficient generation are given. The
features of transverse beam dynamics when transporting the beam
through the linac are investigated. Emphasis is put on the electron
injector which geometry and operation parameters mainly determine
the beam characteristics at the linac exit. Most of the possible
factors contributing to the beam emittance gain in the accelerator
are considered. The obtained analytical estimates are compared to
the numerical simulation results. The experimental results on
compressing and transporting the beam having the electron energy of
5 MeV and the current of 1 kA in the transport system of free
electron laser are presented.
The process of dealumination of mordenites differing in morphology and crystal size obtained under identical conditions from reaction mixtures of similar composition has been studied. Parameters that ...have been chosen to change the morphology and crystal size are the dry matter concentration in the reaction mixture, the pH of the reaction mixture, the crystallization time, the presence of crystalline seeds, and agitation during the synthesis. Dealumination has been performed by heat treatment at 700°C followed by acid treatment. It has been shown that the stability of the mordenite crystal framework to dealumination depends on the thickness of the primary needle crystal, which forms the basis of large zeolite crystals, not on the size of the zeolite crystal as a whole. With a decrease in the average needle crystal thickness from 250 to 90 nm, the Si/Al molar ratio in the crystal lattice, determined from
29
Si NMR data, increases from 6.8 to 9.5. The dealumination is accompanied by a change in the texture of large mordenite crystals associated with a decrease in the packing density of the primary needles.
The high-power long-pulse submillimeter-wave free-electron laser (FEL) is developed jointly by the Institute of Nuclear Physics and the Institute of Applied Physics on the basis of the linear ...induction accelerator complex, which forms electron beams with a particle energy of 5–20 MeV, a current of 2 kA, and a duration of 200 ns. The studies are aimed at achieving power levels of 0.1–1.0 GW and an energy of 10–100 J in pulses of radiation in the indicated range. We present the results of electron-optical experiments, in which electron beams with parameters acceptable for their efficient application in FELs were formed. Helical pulse undulators have been developed for the build-up of operating transverse oscillations of electrons. The possibility to use modified Bragg cavities, which are based on the coupling of propagating and quasi-critical waves and capable of ensuring stable narrow-band generation at significantly large (as compared with the wavelength) transverse dimensions of the interaction space, is analyzed as the key component of the electrodynamic system of a generator. The results of the simulating and cold testing of this type of cavities for operation in the submillimeter-wave range with a channel diameter exceeding 20 wavelengths are presented.
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The possibility of increase in Ti6A14V alloy’s wear resistance is shown using cathodic plasma electrolytic nitriding in a solution of ammonium chloride and ammonia. A competing effect on the ...surface erosion was revealed under the discharges and high-temperature oxidation on the surface morphology and roughness. The complex effect was established on the surface roughness and surface layer hardness of the titanium alloy’s wear resistance. It was determined that the highest decrease in the mass wear by 2.7 times was observed in the samples with a maximum microhardness of the surface layer, reaching 820 HV, and the lowest roughness of the surface. It was shown that the friction coefficient decreased proportionally to the treatment duration, when the surface layer was of not-too-high hardness that benefits the counterbody’s sliding motion.
The acoustic signal dynamics in a five-layer medium containing two liquid layers with polydisperse gas bubbles has been investigated. Calculations have been made for the interaction between the pulse ...perturbation of smallamplitude pressure and a multilayer sample containing two layers of industrial gel with polydisperse air bubbles. It has been shown that a small content of bubbles (about 0.1 vol. %) in a thin gel layer decreases tenfold or more the amplitude of acoustic waves with frequencies close to the resonance frequency of natural oscillations of bubbles. There are frequency ranges thereby where the influence of the bubbly layer is insignificant.
This article theoretically investigates the acoustic waves propagation in bubbly liquids in the presence of diffusion mass transfer. Numerical calculations of the dynamics of pressure pulse in bubbly ...liquids are performed for different values of the vapor concentration. An increase the vapor concentration in the bubbles leads to a decrease in the propagation velocity of the low-frequency harmonics that make up the pulse and to an increase their attenuation due to the nature of the dependence of the phase velocity and attenuation coefficient on the vapor content in the gas bubbles.
Abstract
As the injector of the new fourth-generation SKIF
synchrotron light source at the BINP SB RAS (Novosibirsk, Russia),
the linear accelerator will provide a 200 MeV electron beam. A
precise ...measurement of the beam is very important for the control of
the linac and even the entire light source. A set of diagnostic
instruments for tuning the linac and measuring the beam parameters
starting from the electron RF gun to the output of accelerator has
been designed. The instrumentation should cover the dynamic
diagnostic range of 0.6 to 200 MeV and a beam duration from the
initial 100 ps to 3 ps at the output of the accelerator. The set
includes eight fluorescent screens to measure beam transverse size,
two Cherenkov probes and RF-cavity sensors to record beam duration,
a dipole magnetic spectrometer to measure energy and energy spread,
a Faraday cup (FC) and fast current transformers (FCTs) to measure
beam charge current, and beam position monitors (BPMs) to check the
beam position. This paper aims to give an overview of the beam
instrumentation and briefly describes the design and parameters of
each diagnostic system. The results of numerical and dynamics
simulations of some of the instruments are briefed. Possible
scenarios of linac tuning are discussed.
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