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Systems Based on BN
Published in Vasyl Tomashyk, Quaternary Alloys Based on III-V Semiconductors, 2018
The Ba8[BN2]5F quaternary compound, which crystallizes in the triclinic structure with the lattice parameters a = 420.4 ± 0.3, b = 2092 ± 2, and c = 2095 ± 2 pm and α = 91.74° ± 0.06°, β = 90.03° ± 0.06°, and γ = 93.12° ± 0.07° and a calculated density of 4.739 g·cm−3, is formed in the B–Ba–F–N system (Rohrer and Nesper 1999a). This compound was synthesized from stoichiometric amounts of Ba3N2, BaF2, and BN. The basic educts are well mixed and heated in stainless steel ampoules to 1000°C. The temperature was kept for 10 h and then lowered to room temperature by 50°C·h−1. The product was a mixture of yellow needles, which were intergrown and light yellow crystals of rod-like shape.
Scintillation Detectors and Materials Scintillation Detectors and Materials
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Barium fluoride is a commercially available scintillator that is slightly hygroscopic. It is relatively soft with a ranking of 3 on the Moh hardness scale. The mass density of BaF2 is 4.88 g cm−3, and the atomic numbers of the elemental constituents are 56 and 9. The primary interaction efficiency as a function of gamma-ray energy and detector thickness is shown in Fig. 13.15. It has two important luminescent emissions at 310 nm and 220 nm, both intrinsic emissions. The 310 nm luminescent emission has a decay constant τ of 630 ns, while the 220 luminescent emission has a much faster decay constant ranging between 600 to 800 ps. The refractive index of BaF2 at 220 nm is 1.54 and at 310 nm it is 1.50, both practically the same as common glass windows on PMTs. Pure BaF2 was initially studied by Faruhki and Swinehart in 1971, although there was no report of the short wavelength component at the time. The absorption of light in common soda-lime glass is much too high to allow the transmission of either of the two luminescent wavelengths. Although some borosilicate glasses can be used for the 310 nm emissions, they are inadequate for transmittance of the 220 nm emissions. Perhaps it is for this reason that the fast luminescent component remained unreported until 1983 [Laval et al. 1983]. Instead, a PMT with a fused quartz window is preferred if the 220 nm wavelength is to be used (see Chapter 14 on PMTs). Light yield for the slow component (310 nm) is about 10,000 photons/MeV and for the fast component (220 nm) is about 1,800 photons/MeV.
The specific features of low-temperature thermal properties of the heterovalent (BaF2)0.59(TmF3)0.41 solid solution
Published in Philosophical Magazine, 2022
Vladimir Novikov, Аnton Morozov, Аleksandr Matovnikov, Nikolay Mitroshenkov, Sergey Kuznetsov, Angelina Volchek, Boris Kornev
Barium difluoride, BaF2, has a cubic fluorite crystal structure with space group Fmm and four formula units per unit cell. The metal atoms are located at the vertices and centres of the faces of the elementary cube and each fluorine atom is connected to the metal atoms at the vertices of the cube with three atoms at the centres of the faces by tetrahedral bonds, as shown in Figure 1 [1–3].
Experimental and Numerical Analysis of Thermal Interaction Between Two Droplets in Spray Cooling of Heated Surfaces
Published in Heat Transfer Engineering, 2018
Paolo E. Santangelo, Mauro A. Corticelli, Paolo Tartarini
The employed experimental setup (Figure 1) and approach are thoroughly described in previous works [11, 12, 23]. The facility was built to evaluate the evaporative transient by measuring the solid/liquid interface temperature from below. An infrared thermocamera (Avio TVS-500) was used [11, 12, 22–24]: it carries a micro-bolometric FPA sensor operating in the spectral band 8–12 µm; it features an IEEE-1394 interface and automatic calibration. Its maximum acquisition frequency is 60 frames per second and this parameter was set as 10 frames per second in the present work. The camera axis was placed perpendicular to the deposition region (Figure 1). A close-up lens was applied to enhance the image-resolution ratio (1 pixel to 142 µm); the distance between the lens and the sampling region was set as 150 mm. As shown in the detail of Figure 1, the solid substrate consists of a Barium Fluoride (BaF2) infrared-transparent disk, the spectral transmittance of which is higher than 90% over the most part of the wavelength range 8 – 12 µm [25]. BaF2 thermal conductivity is 11.72 Wm−1 °C−1[23, 25]. The disk diameter and thickness are 74.57 and 3.00 mm respectively; the disk was inserted into a Polystyrene insulating slab, thus minimizing heat losses along radial direction. The actual deposition surface was the disk upper one, where a black-acrylic coating layer was spray-deposited (Figure 1). The layer thickness was measured by a digital micrometer as 54 ± 1 µm, remarkably greater than the maximum operative wavelength of infrared thermocameras, while being thin enough to assume the temperature difference between the upper and the lower coating surface as negligible. Thermal conductivity of the black layer is 0.15 Wm−1 °C−1[26]; its emissivity and absorptance are almost equal to 1, thus allowing to consider its surface as a blackbody. Four radiant panels heated the layer top surface throughout each experiment; as the desired surface temperature was reached, the panels were kept on during droplet deposition, evaporation and surface thermal recovery. A 3-phase power supply controlled by a Variac fed the panels: the applied voltage was varied to impose the radiant flux corresponding to the desired initial surface temperature (nominally 80 °C). A maximum gap of 0.2 °C over the whole interrogation region was allowed; the global irradiated heat flux was measured by a photo-radiometer as about 600 Wm−2.