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X-ray backscatter imaging can be used for a wide range of imaging applications, in particular for industrial inspection and portal security. Currently, the application of this imaging technique to the detection of landmines is limited due to the surrounding sand or soil strongly attenuating the 10s to 100s of keV X-rays required for backscatter imaging. Here, we introduce a new approach involving a 140 MeV short-pulse (< 100 fs) electron beam generated by laser wakefield acceleration to probe the sample, which produces Bremsstrahlung X-rays within the sample enabling greater depths to be imaged. A variety of detector and scintillator configurations are examined, with the best time response seen from an absorptive coated BaF2 scintillator with a bandpass filter to remove the slow scintillation emission components. An X-ray backscatter image of an array of different density and atomic number items is demonstrated. The use of a compact laser wakefield accelerator to generate the electron source, combined with the rapid development of more compact, efficient and higher repetition rate high power laser systems will make this system feasible for applications in the field. Content includes material subject to Dstl (c) Crown copyright (2014). Licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-governmentlicence/ version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@ nationalarchives.gsi.gov.uk [ABSTRACT FROM AUTHOR]

The glasses in the ZrF 4 –BiF 3 –BaF 2 system with different content of bismuth trifluoride have been investigated. The trends of the decrease of glass transition and crystallization temperatures along with the increase of the BiF 3 content in glass, the presence of more than one crystallization peak and composition of crystalline phases in glasses have been revealed. All the studied glasses of the fluorozirconate series have nanosized heterogeneities of virtually the same scale. The crystallization process depends on the bismuth trifluoride content in glass. The contribution of photoluminescence of bismuth with transition emission 540 nm was found for the glass doped with 1% Bi. [ABSTRACT FROM AUTHOR]

Thin films of thallium based superconductors were prepared successfully using sputtering target fabricated as a mixture of barium fluoride, calcium fluoride and copper oxide. Such a target is stable, does not degrade and does not involve any special handling (vacuum or argon atmosphere storage). Precursor films sputtered from this target contained less than 5 at.% of fluorine so no fluorine content reduction is needed. Depending on the substrate, film thickness and synthesis conditions, Tl-2212 phase or a mixture of Tl-2212 and Tl-2223 phases was prepared. Although Tl-2212 phase has epitaxial character, Tl-2223 phase, growing on the top of Tl-2212, is only c -axis oriented. The highest values of T C0 were obtained using 300 nm thick precursor films thallinated at 860 °C. After the thallination the films contained a mixture of Tl-2212 and Tl-2223 phase with a critical temperature of T C0 = 106 K and a critical current density (at 77 K) up to 6 × 10 4 A/cm 2 . Lower T C0 and J C values suggest that further optimization of the film synthesis is needed; however, the first results show that the stable sputtering target prepared from fluorides is a good candidate for high quality Tl-based thin film fabrication. [ABSTRACT FROM AUTHOR]

This work demonstrated that barium fluoride (BaF2) nanocrystals can be controllably formed by an electric-assisted phase separation and precipitation method, EAPSP, in a water/ethanol mixture. Experimentally, we employed an electrostatic generator to provide various voltages to reduce the surface tension of a water/ethanol mixture to cause rapid phase separation after which BaF2 nanocrystals formed and precipitated under control. Results showed that the average diameter of the formed BaF2 nanocrystals was reduced with the voltage increase, e.g. the 0 V sample at about 70 nm in diameter, the 500 V sample at 50 nm in diameter and the 1000 V sample at 30 nm in diameter. The conductivity of these nanocrystals was found to increase with the decrease in size. [ABSTRACT FROM AUTHOR]

Analysis of crystallization kinetics in glasses is an essential tool to gain control over ceramization to achieve desired functionalities. Here, the non-isothermal kinetics of crystallization in two different oxyfluoride glasses have been analyzed using various well-established kinetic models. Activation energies ( E a ) have been estimated using Kissinger, Augis–Bennett and Ozawa methods while both E a and Avrami index ( n ) were predicted from the Matusita and Avrami–Erofeev models. The values of E a and n as predicted using Avrami–Erofeev model are 285 kJ/mol and 1.18, respectively for the oxyfluoride glass yielding BaF 2 nanocrystals whereas 269 kJ/mol and 1.33 for the glass yielding BaGdF 5 nanocrystals. The Avrami indices predict three dimensional diffusion controlled crystallization through bulk nucleation. Moreover, isothermal prediction facilitated to optimize the ceramization temperature and time for obtaining transparent oxyfluoride glass-ceramics. Furthermore, Model-free kinetics analysis demonstrates initial decrease followed by a subsequent rise in activation energy during crystallisation in both the glass systems. [ABSTRACT FROM AUTHOR]

Laser selective excitation and polarization studies of the dominant C 3v symmetry Pr 3+ centre in BaF 2 :0.1%Pr 3+ crystals have been carried out in the 10–75 K temperature range. Crystal-field energy levels for seven of the 12 multiplets of Pr 3+ have been derived and their irrep symmetry labels determined. A further two minor centres have also been identified; their fluorescence lifetimes for the 1 D 2 multiplet are much less than that of the C 3v symmetry centre. [ABSTRACT FROM AUTHOR]

Crystals of fluorite phases with the CaF 2 structure: Ba 1− x La x F 2+ x (x = 0, 0.05, 0.105, 0.25, 0.35, 0.40) and those of tysonite ones with the LaF 3 structure: La 1− y Ba y F 3− y (y = 0, 0.05, 0.09) have been studied by electron diffraction and elemental analysis in a transmission electron microscope. Diffraction patterns of Ba 1− x La x F 2+ x crystals with x = 0.105, 0.25 exhibit diffuse scattering, which indicates the presence of clusters of structural defects. Blurred supercell reflections are seen in diffraction patterns of Ba 1− x La x F 2+ x crystals with a high lanthanum content (x = 0.35, 0.40) in addition to diffuse scattering. They indicate the existence of nanoscale ordered crystallites as well as clusters. It was found that LaF 3 and the tysonite phase La 1− y Ba y F 3− y with a low barium content (y = 0.05) is of a low-temperature l -form (space group P 3 ¯ c 1 , Z = 6). A small fraction of tysonite crystallites in La 1- y Ba y F 3- y crystals with y = 0.09 is of a high-temperature h -form (space group P6 3 /mmc , Z = 2). An intermediate crystal structure between l - and h -forms was also found. The maximum ionic conductivity σ dc of tysonite crystals La 1− y Ba y F 3− y at 293 K is 800 times higher than that of fluorite ones Ba 1− x La x F 2+ x. A correlation was found between logarithm of conductivity and composition: lg σ dc (x) = ax + b for fluorite Ba 1− x La x F 2+ x and tysonite La 1− y Ba y F 3− y crystals. The reason for the additive law of change in ionic conductivity in both types of nonstoichiometric phases in the BaF 2 -LaF 3 system is apparently the similarity of defect structures of fluorite and tysonite phases. • Crystals of fluorite phases Ba 1− x La x F 2+ x and those of tysonite ones La 1− y Ba y F 3− y have been studied. • It was found that LaF 3 and the tysonite phase La 1− y Ba y F 3− y with a low barium content is of a low-temperature l -form P 3 ¯ c 1. • A small fraction of tysonite crystallites in La 1- y Ba y F 3- y crystals with y = 0.09 is of a high-temperature h -form. • The maximum ionic conductivity σ dc of tysonite crystals at 293 K is 800 times higher than that of fluorite ones. • A correlation was found between logarithm of conductivity and composition: lg σ dc (x) = ax + b for fluorite and tysonite crystals. [ABSTRACT FROM AUTHOR]

Barium fluoride, an inorganic scintillation material used for the detection of X-ray and/or gamma-ray radiation, has been receiving increasing attention in the field of radiation measurements in fast-timing applications. To make full use of its timing properties, its slow emission around the ultraviolet region, more specifically, the 300 nm region needs to be suppressed. Although doping ions, such as lanthanum, yttrium, and cadmium, can suppress the slow component, such techniques can lose information of interacted radiations. Consequently, a suppression technique that does not suffer from information loss while maintaining precise timing measurements would be desirable. In this study, we proposed aluminum nano-disk-based plasmonic filters to suppress slow emissions while maintaining fast emissions around 195 and 220 nm and a usability of the slow component. Finite-difference time-domain simulations and experimental results exhibited good agreement, with over 90% of slow components being adequately suppressed without sacrificing fast components, proving that aluminum nanodisks can be used for ultraviolet filters. Moreover, based on the designed filter performance, we conducted coincidence time resolution simulations for positron-electron annihilation gamma rays from an analytical perspective. The simulations indicated the designed filters could maintain high timing performance. Consequently, the proposed plasmonic ultraviolet filter was suitable for maximizing the potential of barium fluoride scintillators., (© 2023 the author(s), published by De Gruyter, Berlin/Boston.)

Pulsed laser deposition was employed to deposit epitaxial Ge2Sb2Te5-layers on the (111) plane of BaF2 single crystal substrates. X-ray diffraction measurements show a process temperature window for epitaxial growth between 85 °C and 295 °C. No crystalline growth is observed for lower temperatures, whereas higher temperatures lead to strong desorption of the film constituents. The films are of hexagonal structure with lattice parameters consistent with existing models. X-ray pole figure measurements reveal that the films grow with one single out-of-plane crystal orientation, but rotational twin domains are present. The out-of-plane epitaxial relationship is determined to be Ge2Sb2Te5(0001) || BaF2(111), whereas the in-plane relationship is characterized by two directions, i.e., Ge2Sb2Te5 [-12-10] || BaF2[1-10] and Ge2Sb2Te5[1-210] || BaF2[1-10]. Aberrationcorrected high-resolution scanning transmission electron microscopy was used to resolve the local atomic structure and confirm the hexagonal structure of the films. [ABSTRACT FROM AUTHOR]

A strong red-emitting Eu2+ activated CaAlSiN3 phosphor was successfully prepared by a pressureless low temperature solid-state reaction method with the aid of fluxes, namely BaF2, CaF2, NH4F, and H3BO3. The experimental results showed that the addition of BaF2 flux effectively reduced the temperature of formation of CaAlSiN3:Eu2+ by about 100 K and suppressed the volatilization of the raw materials, suggesting that BaF2 flux modifies the mechanism of formation of CaAlSiN3:Eu2+. The powder of the CaAlSiN3:Eu2+ phosphor produced with 6 wt% BaF2 flux had an enhanced emission intensity, which was a result of the high crystallinity, the absence of secondary phases, the narrow particle-size distribution, and the clean surfaces of the particles in the final product. [ABSTRACT FROM AUTHOR]

The vitrification in two sets of fluorozirconate glass 53.5ZrF · 20NaF · 20BaF · (6.5 − x)LaF · xEuF (0 ≤ x ≤ 6.5 mol %) (I) and 53.5ZrF · 20NaF · (20 − x)BaF · 6.5LaF · xEuF (0 ≤ x ≤ 20 mol %) (II) has been studied. It has been determined that, in set I, at full or partial replacement of lanthanum fluoride by europium difluoride (1-6.5 mol %), colorless transparent glass is formed. In the samples of set II, at the substitution of BaF in order to obtain stable glass under analogous conditions, the initial batch should not contain more than 7.0 mol % EuF. The methods of differential-thermal and X-ray phase analyses and IR and electron spectroscopy were used to study the properties and phase composition of the obtained glass and vitrocrystalline materials. Using the Grubi criterion, the optimal, with respect to crystallization, EuF content has been deter-mined in the glass of both systems. In the devitrified glass of series II, the low-temperature modification of compound EuZrF is formed, in addition to sodium, barium, and lanthanum fluorozirconates. For the vitro-crystalline samples, the absorption bands of Eu-F bonds are observed in infrared spectra, in addition to the broad band (∼500 cm), which is intrinsic for all fluorozirconate glass. The electron diffuse reflection spectra confirm the presence of both double and triple-charged europium ions in glass. [ABSTRACT FROM AUTHOR]

This study describes the determination of fluorine evaluating the molecular absorption of barium monofluoride (BaF) at the rotational lines of 495.088 and 495.263 nm simultaneously using a high-resolution continuum source electrothermal atomic absorption spectrometer. Upon pipetting of samples together with Ba as its nitrate, BaF was generated in the gas-phase of the atomizer. All experiments were performed using pyrolytically coated graphite tubes/platforms and applying 900 °C for pyrolysis and 2200 °C for vaporization. In the presence of 50 μg of Ba, a perfect linearity up to 0.1 μg of F was maintained. The limit of detection and characteristic mass of the method were 0.105 ng and 0.055 ng of F, respectively. The F concentration of a standard waste water sample was found in the uncertainty limits of its certified value as well as spike additions were quantitatively recovered. Finally, F concentrations in various water and milk samples sold in markets were determined. [ABSTRACT FROM AUTHOR]

The Barium fluoride loaded titanium dioxide (BaF 2 –TiO 2 ), synthesized by a sonochemical method, was characterized for morphological and optical characteristics. DRS spectra reveal a slight increase in absorbance from 400 nm to entire visible region in BaF 2 loaded TiO 2 . Presence of BaF 2 was confirmed by X-ray photoelectron spectroscopy analysis. BaF 2 –TiO 2 is found to be more efficient than prepared TiO 2 and commercial TiO 2 -P25 at pH 5 in the degradation of Trypan Blue under solar light. The effects of operational parameters such as the amount of photocatalyst, initial pH on photomineralization by BaF 2 –TiO 2 have been analyzed. The degradation intermediates identified by gas chromatography-mass spectrometry analysis are Naphthalen-1-ol, 2-aminobenzaldehyde and 5-aminobenzene-1,3-diol. A dual mechanism involving electron–hole separation by BaF 2 –TiO 2 and dye sensitization is proposed for the degradation under solar light. The mineralization of TB was confirmed by FT-IR, COD and CV measurements. The catalyst was found to be reusable. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mo reacted with BaF2 and formed BaMoO4. [•] The working temperature range of Fe–Cr based alloy was widened. [•] Tribological properties of composites strongly depended on the additives. [•] FM showed the excellent tribological properties from RT to 800°C. [ABSTRACT FROM AUTHOR]

We experimentally investigate the spectral extent and spectral profile of the supercontinuum (SC) generated in transparent solids: barium fluoride, calcium fluoride, and fused silica upon irradiation by intense femtosecond-long pulses of 800, 1,380, and 2,200 nm light. These wavelengths correspond to the normal and anomalous group velocity dispersion (GVD) regimes in fused silica calcium fluoride and barium fluoride. We observe an isolated (anti-Stokes) wing on the blue side most prominently in fused silica but also in CaF. The SC conversion efficiency is measured for the long wavelengths used in our experiments. We also present results on filamentation in BaF in the anomalous GVD regime, including visualization of focusing-refocusing events within the crystal; the size of a single filament is also determined. The 15-photon absorption cross section in BaF is deduced to be 6.5 × 10 cmWs. [ABSTRACT FROM AUTHOR]

Incorrect choice of measuring experimental geometry and energy windows for a positron-lifetime spectrometer with BaF2 scintillators can lead to a significant distortion in a measured spectrum. Contribution of the distorted events for a non-optimal geometry may exceed 50%. It reduces the measured lifetimes of the spectral components and redistributes their intensities. The Geant4 simulation allows to estimate an influence of the measuring geometry on the spectrum distortion and to choose the most appropriate energy windows. The optimal geometry with a lead absorber between detectors suppresses contribution of the distorted coincidences down to 1% providing sufficiently high count rate of true events. [ABSTRACT FROM AUTHOR]

The spectral characteristics of BaF and BaF:Tm crystals and ceramics are compared. The vacuum UV (VUV) and UV absorption spectra and excitation spectra of core-valence and exciton luminescence are investigated. The main exciton and electron-hole processes responsible for the structure of recorded spectra are considered. [ABSTRACT FROM AUTHOR]

The barium fluorobromate (III) has been obtained as the product of interaction between barium fluoride and bromine (III) trifluoride. The heat of formation of Ba (BrF 4 ) 2 has been found by the isothermal calorimetry method. By the TG/DT analysis the thermal stability of Ba(BrF 4 ) 2 has been researched. It has been found that this compound was mostly stable in the atmosphere or argon up to 250 o C. [ABSTRACT FROM AUTHOR]

Highlights: [•] The 1st observation of surface nanostructures induced by irradiation of BaF2 surface with highly charged ions (HCI) at higher potential energy is shown. [•] Evidence for the significance of the deposited potential energy in the creation of surface hillocks in BaF2 is confirmed. [•] The existence of potential energy threshold for the creation of surface etch pits in CaF2 is shown. [•] Similarities and differences for the creation of HCI-induced nanohillocks and etch pits in CaF2 and BaF2 of the same crystalline structure are discussed. [•] We compare the results with modifications induced by swift heavy ions. [ABSTRACT FROM AUTHOR]

Radiation defects in barium fluoride single crystals doped with cadmium have been investigated by luminescence and absorption spectroscopy, as well as by electron spin resonance spectroscopy. Three types of Cd [ABSTRACT FROM AUTHOR]

This paper examines how the transformation of BaF from a single-crystalline to polycrystalline state as a result of uniaxial hot-forming influences its properties. With increasing strain, the microstructure of the material changes from a nonuniform polycrystalline one, with a block size of about 1 mm, to a classic ceramic structure made up of grains in which dislocations form walls, resulting in a subgrain structure. The best mechanical characteristics are offered by the ceramic produced at a strain on the order of 700%. The intensity of the fast X-ray luminescence component (band at 220 nm) is independent of strain, whereas that of the slow component (band at 310 nm) decreases with increasing strain. [ABSTRACT FROM AUTHOR]

Abstract: Absorption and site-selective laser spectroscopy of BaF2 single crystals homogeneously doped with Nd3+ ions as well as heterogeneously doped with Nd3+ and either Gd3+ or Yb3+ ions, performed at 10K, is presented. In each case a single centre, assigned to be of C3v symmetry, is dominant. A heterogeneous Nd3+–RE3+ (RE being either Nd or Yb) is also present in each of the double doped crystals. Energy levels for six multiplets of the single Nd3+ centre and for three multiplets for each Nd3+–RE3+ centre are presented together with the 4F3/2 (R) multiplet fluorescence lifetime for each centre. Calculations give comparable solution energies for C3v and C4v symmetry Nd3+ centres in BaF2; the C3v symmetry configuration has lower energy for the preceding lanthanides while C4v is favoured from Sm3+ onwards. [Copyright &y& Elsevier]

Red phosphors BaTiF6:Mn4+ with microrod and polyhedron morphologies have been prepared respectively by etching TiO2 and Ti(OC4H9)4 in a HF solution with an optimized concentration of KMnO4 at 1.5 mmol L-1 in hydrothermal conditions. The red phosphor BaTiF6:Mn4+ exhibits a broad excitation band in the blue region and sharp emission peaks in the red region. A white LED (WLED) fabricated with the red phosphor BaTiF6:Mn4+ shows "warm" white light that possesses a color rendering index of 93.13 at a color temperature of 4073.1 K. [ABSTRACT FROM AUTHOR]

Sumfrequency generation (SFG) vibrational spectroscopy and contactangle measurements of an ionic liquid, 1-butyl-3-methylimidazoliumdicyanamide [BMIM][DCA], at solid–liquid interfaces are reported.Bare solid single crystal BaF2(111) surface, a singleand few layer graphene-coated BaF2(111) surface are usedas the solid substrates. The SFG results indicate that both [BMIM]+and [DCA]−can be detected specificallyon the graphene-coated BaF2(111) surface, without coatingonly [DCA]−are observed. [DCA]−anions are attracted to the positively charged BaF2(111)surface and occupy the first layer at the solid–liquid interface.The graphene coating shields the charged crystal surface and allowsboth cations and anions to exist at the interface. Furthermore, increasein the contact angle of BaF2surface after graphene layersdeposition suggests that the graphene coating lowers the surface energy. [ABSTRACT FROM AUTHOR]

Single crystals of pure and Eu2+ doped LiBaF3 have been grown from melt by using a vertical Bridgman–Stockbarger method. Effects induced by irradiation on europium doped LiBaF3 (lithium barium fluoride) single crystals were monitored by optical absorption, photoluminescence and thermoluminescence studies. The absorption bands of Eu2+ ions with peaks at 240, 290 and 320nm were observed in the LiBaF3:Eu2+ crystal. Drastic increase in absorption was noted below 600nm after gamma irradiation, which was dependent on the radiation dose. The additional absorption peak at around 570nm was observed in irradiated crystal due to the ionization process Eu2+(−)e−→Eu3+. Photoluminescence of Eu2+ doped LiBaF3 single crystal shows sharp line peaked at ~359nm and a broad band extending between 370 and 450nm which shows a considerable reduction in Eu2+ PL intensity after gamma irradiation. Irradiated LiBaF3:Eu2+ sample has revealed three intense TL glow peaks at 128°C (peak-1), 281°C (peak-2) and 407°C (peak-3). Activation energy (E) and frequency factor (s) of the latter two peaks were determined by various heating rate (VHR) method and graphical method. [ABSTRACT FROM AUTHOR]

Fourier transform-infrared (FT-IR) chemical imaging in transmission mode has traditionally been performed on expensive mid-IR transparent windows such as barium/calcium fluoride, which are more fragile than glass, making preparation in the histopathology laboratories more cumbersome. A solution is presented here by using cheap glass substrates for the FT-IR chemical imaging, which has a high-wavenumber transmission window allowing measurement of the C–H, N–H, and O–H stretches occurring at ca. 2500–3800 cm–1. The "fingerprint" region of the IR spectrum occurring below 1800 cm–1 is not obtainable; however, we demonstrate that a wealth of information is contained in the high wavenumber range using 71 patients on a breast tissue microarray (TMA) as a model for investigation. Importantly, we demonstrate that the tissue can be classified into four basic tissue cell types and that using just the epithelial cells, reasonable discrimination of normal and malignant tissue can be found. [ABSTRACT FROM AUTHOR]

In this work, PbSe QDs were precipitated in oxyfluoride glass-ceramics containing BaF2 nanocrystals. Tunable and broad absorption and photoluminescence from PbSe QDs doped glass-ceramics were observed in the near-infrared wavelength range. When the glasses were heat-treated at temperatures below 560°C using one-step heat-treatment schedule, single photoluminescence band was observed from each sample. Upon high temperature (560°C or 570°C) one-step or two-step heat-treatment, dual-band photoluminescence was observed. These two photoluminescence bands in each spectrum were separated by a gap of ~110–150meV, and as a result, effective full width at half maximum as large as ~500nm was recorded. [ABSTRACT FROM AUTHOR]