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Morphology of Spray-Freeze-Dried Products
Published in S. Padma Ishwarya, Spray-Freeze-Drying of Foods and Bioproducts, 2022
The scanning electron microscope is a well-known instrument to visualize and understand the intricacies of a material's microstructure. It provides information on the topographies, morphology, compositional differences, crystal structures and orientation of a material (Swapp, n.d.). As the name suggests, a scanning electron microscope uses electrons instead of light to form an image. An electron gun generates the electrons that are accelerated to moderately high energy and focused upon the sample using electromagnetic fields. Interaction between these electrons and the atoms in the specimen produces a signal. Each spot on the sample interacts with the electron beam and emits secondary electrons from its surface, which are counted by a detector that directs the signals to an amplifier (JEOL, n.d.). The final micrograph thus obtained is collated from all the electrons emitted from each spot on the sample.
Maxwell’s theory of electromagnetism
Published in Edward J. Rothwell, Michael J. Cloud, Electromagnetics, 2018
Edward J. Rothwell, Michael J. Cloud
An electron gun creates a collimated stream of electrons for use in, e.g., a cathode ray tube, a microwave source or amplifier, or an electron microscope. A heated cathode emits electrons with low initial velocity v0 $ \mathbf{v}_0 $ , which are then accelerated in a static electric field. The electric field is created by applying a voltage between the cathode and an anode, separated by a distance d so that E0=-x^V0/d $ \mathbf{E}_0=-\hat{\mathbf{x}}V_0 /d $ (Figure 2.11). Consider an electron emitted at the origin at time t=0 $ t=0 $ . Determine the speed and kinetic energy of the electron when it passes through the anode at x=d $ x=d $ .
2 Lasers
Published in Peter K. Cheo, Handbook of Molecular Lasers, 2018
In a plasma cathode, electrons are extracted from a low-density plasma specially created for each emission event. Often, such cathodes use no auxiliary heater power supply to create the plasma (hence the name “cold” cathode); the plasma creation process is initiated by the application of the electron gun voltage pulse itself. Cold cathodes are used in several geometries: The foil-edge cathode, where the emission is confined to a very narrow region such as the edge of one or more thin foils or a thin strip of upright fibers. In the absence of an external guide magnetic field, electron optics can be used to expand the beam so that its area at the laser gas interface is much larger. The Los Alamos Helios laser electron gun used this design.The extended cathode, which usually uses a graphite velvet or brush surface whose area is comparable to the required beam area at the laser-gas interface. The electron beam flow is rectilinear. This design is particularly suitable for intense beams requiring a guide magnetic field to avoid pinching. Graphite is a favorite material because a plasma forms at the tips of the carbon filaments with particular ease when the external electric field pulse is applied (but the consequences of the deposition of carbon debris on the electron gun chamber surface need to be considered). This cathode geometry is usually used in excimer lasers such as the Los Alamos Large Aperture Module, where the cathode area is 1 m × 2 m (see Fig. 5.8).The “spark” cathode, a sparse version of the extended cathode. The physical cathode area is comparable to the final beam area, but the plasma is produced by arc formation made to occur at a large number of point locations within the physical cathode boundaries. Often, one employs an array of small metal “dots” insulated from the main body of the cathode but coupled capacitively to it (and to ground). Upon application of the electron gun pulse, the dots assume a potential determined by the capacitative voltage division; the potential difference is large enough to cause an arc to occur between the dot and the cathode substrate. The process is illustrated in Fig. 5.9.
Evaluation of the cellular effects of silica particles used for dermal application
Published in Journal of Toxicology and Environmental Health, Part A, 2023
Masanori Horie, Haruhisa Kato, Ayako Nakamura, Yutaka Kadota, Naoyuki Izumi
FE-SEM measurements; A scanning transmission electron microscope (Quanta 250 FEG, FEI Co., USA) using a field emission electron gun was employed. The electron diffraction of the selected area was operated at 2–20 kV with secondary electrons in a high-vacuum mode. The samples were prepared on treated hydrophilic flat silicon wafers. The sizes of the silica nanoparticles were assessed by the Scandium 5.1 software (Olympus Soft Imaging Systems, Japan). The scale was verified against the AS100P-D calibration scale, which has AIST traceability (NTT advanced Technology corporation, Japan). In order to determine the concentration of the silica particles, one drop of each fraction was placed on a well-cleaned silicon wafer and the weight of each drop (approximately 0.01 ml) measured. After the samples were dried, all particles in the dried drop were sized and counted (Kato, Nakamura, and Banno 2019). The particle size is the value published by the manufacturer.
Comparison of Analysis Results on Three Methods for Sampling Crud, a Radioactive Corrosion Product with Zinc-Injected Spent PWR Nuclear Fuel Rods
Published in Nuclear Technology, 2021
Yang Hong Jung, Seung Je Baik, Young Gwan Jin
The scanning electron microscope (Philips XL-30) used in this test is a shielded-type with a LaB6 electron gun. Energy dispersive spectrometry (EDS) (EDAX DX-4), which was used for soft and hard crud analyses, is a device with a tantalum collimator installed to reduce the effect of gamma rays. To prepare the test specimens, the vacuum plasma method was used with a gold sputter coater at a current of 10 mA for 6 min. The shielded EPMA used in this study was fabricated to be able to deal with highly irradiated fuels. In order to reduce the influence of radioactivity on the specimen, spectrometry, and column, etc., appropriate parts were shielded with lead and tungsten. The radioactivity of the specimen was designed to be testable up to 0.5 Ci. Beam conditions of 15 kV and 20 nA were applied for crud specimens because the specimen thickness was extremely thin.
Design of a Microfabricated Planar Slow Wave Structure for a 0.22-THz TWT for Communication, Imaging and Remote Sensing
Published in IETE Technical Review, 2019
Major components of a compact planar THz TWT, as shown in Figure 2, are electron gun with high current density cathode for forming a sheet electron beam of suitable shape (rectangular/elliptical) and size at required beam voltage and beam current; slow wave circuit/structure (SWS) in planar geometry of wide bandwidth, high impedance, low loss, and supporting and amplifying THz waves extracting maximum kinetic energy from the sheet electron beam; input and output waveguide couplers to feed THz signal into the circuit and coupled out from the circuit with minimum reflection and minimum insertion loss; periodic permanent magnetic focusing circuit for confined flow of the sheet beam through the structure with minimum beam interception; collector (depressed) for recovering maximum kinetic energy from the spent electron beam with zero back streaming; and complete tube assembly with packaging and potting.