Characteristics of LiAlO2 – Radioluminescence and optically stimulated luminescence

Radioluminescence (RL) and optically stimulated luminescence (OSL) results of LiAlO₂ were compared with Al₂O₃:C. For blue (470 nm) optical stimulation, RL + OSL signal in LiAlO₂ exhibited a sharp initial increase followed by a decay within the first 20 s of continuous wave (CW)-OSL and a very slow increase thereafter. The RL + OSL signal was about 1.25 times of its RL signal in LiAlO₂ as compared to 2.5 times in Al₂O₃:C. With the continued beta irradiation, the RL signal exhibited a faster growth in LiAlO₂ than that in Al₂O₃:C. Emission spectrum of LiAlO₂ exhibited multiple emission peaks in the range from 320 to 380 nm as against 410 nm of Al₂O₃:C. RL and OSL emission spectra were similar in both LiAlO₂ and Al₂O₃:C. The intense RL in LiAlO₂ (about 300 times of that of its background signal) for a beta ray dose rate of 4.6 mGy/s appears attractive for radiation dosimetry including real time/online dosimetry and dose mapping.     

Free-radical saturation at high doses in γ-irradiated glycine

In this work the apparent decrease of radical yield in irradiated dry glycine at very high doses of radiation is interpreted as an effect of measurement inaccuracy due to the spatially inhomogeneous distribution of the radicals and to the presence of a mixture of different types of radical species.     

Thermomechanical response of an Ni–Ti–Cr shape-memory alloy at low and high strain rates

The thermomechanical response of an Ni–Ti–Cr shape-memory alloy is investigated at various initial temperatures, over a wide range of strain rates, using an Instron hydraulic testing machine and one of the modified split-Hopkinson-bar systems at the Center of Excellence for Advanced Materials, University of California, San Diego. The transition stress for the stress-induced martensite formation is observed to be quite sensitive to the initial deformation temperature, but the yield stress of the resulting martensite is not. The linear transition stress–temperature relation with a slope of 8.5?MPa?K^?1, obtained in a quasistatic loading regime, seems to remain valid for strain rates up to 500–700?s^?1. The transition stress and the yield stress of the stress-induced martensite show strain-rate sensitivity, increasing monotonically with increasing strain rate. There exists a certain critical strain rate at which the transition stress equals the yield stress of the material. This critical strain rate determines the material's deformation behaviour; the material deforms by the formation of stress-induced martensites and their subsequent yielding, when the strain rate is less than this critical value, and through dislocation-induced plastic slip of the parent austenite, when the strain rate exceeds the critical value. It appears that the critical strain rate increases slightly with decreasing initial temperature.     

Growth of α-Al2O3:C crystal with highly sensitive optically stimulated luminescence

In this work, an α-Al₂O₃:C crystal was directly grown by the temperature gradient technique (TGT) using Al₂O₃ and graphite powders as the raw materials. The optical, optically stimulated luminescence (OSL) properties and dosimetric characteristics of as-grown crystal were investigated. As-grown α-Al₂O₃:C crystal shows strong absorption band at 205, 230 and 256 nm. Three-dimensional thermoluminescence (TL) emission spectrum of the crystal shows a single emission peak at ∼415 nm. The OSL decay curve can be fitted to two exponentials, the faster component and the slower component. The OSL response of the crystal shows a linear-sublinear-saturation characteristic. As-grown α-Al₂O₃:C crystal shows excellent linearity in the dose range from 5×10⁻⁶ to 50 Gy. For doses higher than the saturation dose (100 Gy), the OSL sensitivity decreases as the dose increases.     

The study on optically stimulated luminescence dosimeter based on the SrS：Eu,Sm and CaS：Eu,Sm

With the increasing use of nuclear energy, there is a need for a wider range of efficient dosimeters for radiation detection and assessment. There has been a tremendous growth in the development of radiation detectors and devices in the past few decades. In recent years, the development of new materials for radiation dosimetry has progressed significantly. Alkaline earth sulfides （AES） have been known for a long time as excellent and versatile phosphor materials. In the present investigation, a number of phosphor samples such as mono-, binary and ternary sulfides of alkaline earths （II^a-VI^b） have been prepared and their TL properties have been studied with respect to exposure （x-ray） response and fading. In this paper, some results on SrS：Eu, Sm and CaS：Eu, Sm phosphors are presented. A type of novel OSL dosimeter is described. The dosimeter takes advantage of the characteristics of charge trapping materials SrS：Eu, Sm and CaS：Eu, Sm that exhibit optically stimulated luminescence （OSL）. The measuring range of the dosimeter is from 0.01 to 1000 Gy. The OSL dosimeters provide capability for remote monitoring radiation locations which are difficult to access and hazardous. This equipment is relatively simple, small in size and has low power consumption. The device is suitable for space radiation dose exploration. In addition, it also can be used in IC and other radiation occasions and has good prospects.     

Thermoluminescence and optically stimulated luminescence disadvantages of α-Al2O3:C crystal grown by the temperature gradient technique

Recently, α-Al₂O₃:C crystal with highly sensitive thermoluminescence (TL) and optically stimulated luminescence (OSL) has been successfully grown by the temperature gradient technique. This paper investigates the heating rate dependence of TL sensitivity, light-induced fading of TL signals and thermal stability of OSL of α-Al₂O₃:C crystals. As the heating rate increases, the integral TL response decreases and the dosimetric glow peak shifts to higher temperatures in α-Al₂O₃:C crystals. Light-induced fading of TL increases with the irradiation dose, and TL response decreases as the exposure time increases, especially in the first 15 minutes. With the increasing intensity of the exposure light, the TL fading of α-Al₂O₃:C crystal increases sharply. The OSL response of as-grown α-Al₂O₃:C crystal is quite stable below 373 K and decreases sharply for higher temperatures.     

Nuclear-like effects in proton–proton collisions at high energy

We show that several effects considered nuclear effects are not nuclear in the sense that they do not only occur in nucleus–nucleus and hadron–nucleus collisions but, as well, they are present in hadron–hadron (proton–proton) collisions. The matter creation mechanism in hh, hA and AA collision is always the same. The p _T suppression of particles produced in large multiplicity events compared to low multiplicity events, the elliptic flow and the Cronin effect are predicted to occur in pp collisions at LHC energies as a consequence of the high density partonic medium obtained.     

Spin crossovers in Mott–Hubbard insulators at high pressures

The high-pressure induced phase transitions initiated by electronic transition in 3d ions from the high-spin (HS) to the low-spin (LS) state (HS-LS spin-crossover) are considered. Behavior of the system with d⁶ electronic configuration is investigated in the ground state of zero temperature and critical pressure P_c. Magnetic properties of the Mott–Hubbard insulator (Mg_1−xFe_x)O are studied in the vicinity of the quantum critical point (T=0, P_c). At the critical pressure of spin crossover P_c, the spin gap energy ε_S between HS and LS states is zero. The quantum spins fluctuations HS⇔LS do not require any energy, and the antiferromagnetism is destroyed in the quantum critical point by the first order transition.     

Oxidation parameters determination of Cu–Al–Ni–Fe shape-memory alloy at high temperatures

In this study, isothermal oxidation behavior of a Cu–Al–Ni–Fe shape-memory alloy between 500 and 900 °C was investigated. Alloy samples were exposed to oxygen by TG/DTA for 1 h at a constant temperature, allowing for calculation of the oxidation constant and activation energy values of the oxidation process. The oxidation constant value increased with temperature, reaching saturation at 800 °C. The effect of oxidation on crystal structure, surface morphology and chemical composition of the Cu–Al–Ni–Fe alloy was determined by X-ray diffractometer (XRD) and scanning electron microscope (SEM)–energy-dispersive X-ray (EDX) analyses. With increasing oxidation temperature, number and intensity of the characteristic 18R martensite phase peaks were reduced while Al₂O₃ phase peaks were increased. In parallel to the XRD results, the same variations were also detected by SEM–EDX measurements.     

Magnetic losses at high flux densities in nonoriented Fe–Si alloys

We present and discuss power loss measurements performed in Fe–(3.5 wt%)Si nonoriented laminations up to very high flux densities. The results are obtained on disk samples using a 1D/2D single-sheet tester, where the fieldmetric and the thermometric methods are applied upon overlapping polarization ranges. The power loss in the highest polarization regimes (e.g. J_p>1.8 T) is measured, in particular, by the rate of rise of temperature method, both under controlled and uncontrolled flux density waveform, the latter case emulating the conditions met in practical unsophisticated experiments. Lack of control at such extreme J_p levels is conducive to strong flux distortion, but the correspondingly measured loss figure can eventually be converted to the one pertaining to sinusoidal induction at the same J_p values. This is demonstrated as a specific application of the statistical theory of magnetic losses, where the usual formulation for the energy losses in magnetic sheets under distorted induction is exploited in reverse fashion.     

Erbium–ytterbium co-doped fiber amplifier operating at 1550 nm with stimulated lasing at 1064 nm

A new method of controlling the amplified spontaneous emission (ASE) from Yb^3 + ions in Er^3 +/Yb^3 + co-doped fiber amplifiers is presented. The 1 μm ASE is suppressed by stimulating a laser emission at 1064 nm in a fiber amplifier, due to a positive feedback for the 1 μm signal. The results are compared to a conventional amplifier setup without any ASE control. We have shown, that applying a feedback loop in an Er^3 +/Yb^3 + co-doped fiber amplifier allows higher power scaling and provides operation without unwanted parasitic lasing effects, increasing the stability and robustness of the amplifier.     

Linear-scaled excited state calculations at linear response time-dependent Hartree–Fock theory

In this paper, we present a localised molecular orbital (LMO) based methodology of the TDHF excited state calculation in which the computing time is linearly scaled by the size of the system. In the benchmark calculations using simple poly-acetylene molecules, the LMO-driven TDHF provides significant shorter CPU time than conventional TDHF calculations and near O(N) computing cost. We also present the techniques accelerating the convergence speed in Davidson iterative diagonalisation and show its usefulness. The methodology accurately reproduces the excited state properties of poly-acetylene molecules obtained in conventional TDHF calculations.     

Effect of metal diffusion into polycrystalline 6H–SiC prior to its anodization on luminescence response

p-Type porous SiC layers were fabricated by anodization of resistive p-type 6H–SiC samples using HF/ethylene glycol solution. Thin films of lithium (Li) and aluminum (Al) as donor and acceptor elements were vacuum deposited and diffused onto SiC substrates prior to anodization. The aim of this work is to investigate the properties of the nanoporous SiC layer formed by this method and to deduce the effect of diffused lithium as donor and Al as acceptor atoms on their photoluminescence response (PL). The profile distribution of lithium and aluminum diffused atoms was carried out using secondary ion mass spectrometry (SIMS). The photoluminescence spectra of the anodized Al-diffused samples exhibit a broad emission band centered at about 475 nm, while the Li-diffused samples exhibit luminescence with one broad peak located at 655 nm, attributed to Li-related defect centers. In addition, the PL intensity of lithium diffused samples varies with varying the etching time. Finally, the results are expected to have important applications in modern optoelectronic devices and electrode materials of lithium batteries.     

Double-sided laser heating system for in situ high pressure–high temperature monochromatic x-ray diffraction at the esrf

A new double-sided laser heating system optimized for monochromatic X-ray diffraction at high pressure and high temperature has been developed at beamline ID27 of the European Synchrotron Radiation Facility (ESRF). The main components of this system including optimized focusing optics to produce a large and homogenous heated area, optimized mirror optics for temperature measurements and a state-of-the-art diffraction setup are described in details. Preliminary data collected at high pressure and high temperature on tungsten and iron are presented.     

Fractional Stokes–Einstein relation in TIP5P water at high temperatures

Fractional Stokes–Einstein relation described by D ～(τ/T)~ξ is observed in supercooled water, where D is the diffusion constant, τ the structural relaxation time, T the temperature, and the exponent ξ =τ~(-1). In this work, the Stokes–Einstein relation in TIP5 P water is examined at high temperatures within 400 K–800 K. Our results indicate that the fractional Stokes–Einstein relation is explicitly existent in TIP5P water at high temperatures, demonstrated by the two usually adopted variants of the Stokes–Einstein relation, D ～τ~(-1)τand D ～ T/τ, as well as by D ～ T/η, where η is the shear viscosity. Both D ～τ~(-1)τand D ～ T/τ are crossed at temperature T_x= 510 K. The D ～τ~(-1)τis in a fractional form as D ～τξwith ξ =-2.09 for T ≤ T_xand otherwise ξ =τ~(-1).25. The D ～ T/τ is valid with ξ =τ~(-1).01 for T ≤ T_xbut in a fractional form for T T_x. The Stokes–Einstein relation D ～ T/η is satisfied below T_x = 620 K but in a fractional form above T_x. We propose that the breakdown of D ～ T/η may result from the system entering into the super critical region, the fractional forms of D ～τ~(-1)τand D ～ T/τ are due to the disruption of the hydration shell and the local tetrahedral structure as well as the increase of the shear viscosity.     

Asymptotics of dispersion curves in time-dependent problems of free viscous–inviscid interaction at transonic speeds

New high-frequency asymptotics of the dispersion relation have been obtained when analyzing the stability of a transonic boundary layer with self-induced pressure. It is shown that the dependence of the perturbation frequency on the wave number (except for the range of small wave numbers), which was previously considered unambiguous, is an exceptional case.     

Germanium–vacancy color center in isotopically enriched diamonds synthesized at high pressures

We report on the high-pressure synthesis of novel nano- and microcrystalline diamonds with germanium–vacancy (Ge–V) color centers emitting at 602 nm. The synthesis was carried out in non-metallic growth systems C–H–Ge and C–H–O–Ge enriched with germanium and carbon isotopes. We demonstrate germanium and carbon isotope shifts in the fine structure of the luminescence, which allows us to unambiguously associate the center with the germanium impurity entering into the diamond lattice. We show that there are two ground-state energy levels with the separation of 0.7 meV and two excited-state levels separated by 4.6 meV in the electronic structure of the center and suggest a split-vacancy structure of this center. High-intensity and narrow-line emission of high-pressure synthesized small diamonds with Ge–V centers makes them promising candidates for single-photon emitters.     

Conductivity anomalies in Y–Ba–Cu–O at 40K and 100K under high quasihydrostatic pressures

Electrical resistance measurements at low temperatures and high quasihydrostatic pressures on superconducting and non-superconducting varieties of Y_0.8Ba_1.2Cu₂O₅ (obtained by annealing in oxygen and air respectively) show striking anomalies in the vicinity of 100K and 40K. Arguments are presented to show that these anomalies as also the occurrence of T 's in the oxide superconductors either in the vicinity of 100K or of 40K are connected with their layered structure containing planes of Cu-O otahedral complexes.