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Radiation Dosimetry
Published in Kwan Hoong Ng, Ngie Min Ung, Robin Hill, Problems and Solutions in Medical Physics, 2023
Kwan Hoong Ng, Ngie Min Ung, Robin Hill
An ionisation chamber operates based on the principle of measuring the number of ion pairs produced in a volume of air due to radiation. In the simplest arrangement, the ionisation chamber exists as two-electrode plates spaced apart in air. A large potential (100–400 V) is applied to the plates. Radiation dose is delivered by charged particles in excitation and ionisation events. Charged particles are either the radiation of interest themselves (e.g., electron and proton radiotherapy) or indirectly produced by non-charged radiation (e.g., photons and neutrons). When charged particles traverse between the plates, they ionise the air producing free negative electrons and positive ions. The positive- and negative-charged particles are then swept by the electric field between the plates towards the appropriate electrodes, producing a steady current flow in the external circuit, which can be measured by an electrometer. The important premise of an ionisation chamber is that each interaction of the charged particle produces exactly one ion pair and therefore allows for accurate quantification of dose.
Basics of Radiation Interactions in Matter
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Most detector systems rely on the measurement of charged particles. This means that a neutron cannot be measured directly because it does not carry any charge. However, one can use some type of neutron interaction process with a large cross section that can create free charged particles, which can then be detected. Three commonly used processes are the (n,p) reaction in 3He, (n,α) in 6Li, and (n,α) in 10B. The last process has also been used clinically to treat cancer in the brain by a method called boron neutron-capture therapy (BNCT). For more information about this, see, for example, the literature review by Nedunchezhian and colleagues [4].
The Structure of Solids
Published in Joseph Datsko, Materials Selection for Design and Manufacturing, 2020
Like-charged particles repel each other and oppositely charged particles attract each other with an electrical force called the coulomb force. When a material is maintained in the solid state by the mutual attraction of positively and negatively charged ions, the interatomic bonding force is called ionic.
A magneto-hydrodynamic analysis of liquid metal flows in the conducting and insulating wall ducts using a finite element tool
Published in International Journal of Ambient Energy, 2023
The fusion reactor is a toroidal-shaped device, in which a plasma ring is confined by twisting the magnetic fields using vacuum vessels (Song et al. 2014a). A plasma is made up of charged particles and confinement of plasma within the walls of the vacuum vessel is achieved using a large magnetic field (Walker et al. 2020). Poloidal and toroidal coils are used to confine the plasma as it follows the magnetic flux lines. Immediately behind the first wall of the fusion reactor, blanket modules are provided through which coolant is passed (Nygren 1981), (Pironti and Walker 2005), (Sykes et al. 2014). Blanket modules have used square straight channels to flow electrically conducting fluid in it. The MHD pressure drop is a severe problem in the fusion reactor and the problems arising from the MHD effects can be interesting for the researchers. Therefore, the study of the MHD analysis in the coupled field environment is very interesting among researchers. In this paper, an extensive analysis has been carried out to reduce the MHD effect in the square channels used for the fusion reactor. A finite element analysis of MHD rotational flow of non-fluid was investigated by (Ali et al. 2020). In (Umavathi et al. 2005), the turbulent two-fluid flow and heat transfer in a horizontal channel were examined. The computational methods have been studied by increasing the field intensity with a significant influence on the fluid flow (Adesanya et al. 2015).
Macroscale modeling of electrostatically charged facemasks
Published in Aerosol Science and Technology, 2023
M. Jamali, S. Atri, S. Gautam, A. M. Saleh, H. V. Tafreshi, B. Pourdeyhimi
Particle capture due to electrostatic attraction is a complicated phenomenon that is not understood well, and relies on hard-to-obtain quantitative information about density and polarity of charges in the media (and among the particles). In this study, we considered three particle charge configurations of neutral particles, charged-neutralized particles, and singly-charged particles (Chang, Chen, and Pui 2016; Chang et al. 2018; Tang et al. 2018; Wang, Liu, and Chen 2020; Wang and Chen 2021). With regards to the fibers, we considered them as corona-charged bipolar fibers. In the first case (the neutral particles), as the particles approach the charged fibers they become polarized by the electric field of the fibers (resulting in induction of dipole charges on the particles). In the second case (charge-neutralized particles), particles were assumed to be in the Boltzmann equilibrium state, i.e., they maintain a zero net-charge (symmetric charge distribution). In the third case (singly-charged particles), the particles were assumed to contain a unit charge (Chang, Chen, and Pui 2016; Chang et al. 2018; Tang et al. 2018; Wang, Liu, and Chen 2020; Wang and Chen 2021). The SFE due to electrostatic capture of neutral particles by charged fibers is given by Lathrache, Fissan, and Neumann (1986) (see also O’Shaughnessy 2022),
Biomaterial engineering surface to control polymicrobial dental implant-related infections: focusing on disease modulating factors and coatings development
Published in Expert Review of Medical Devices, 2023
Samuel S. Malheiros, Bruna E. Nagay, Martinna M. Bertolini, Erica D. de Avila, Jamil A. Shibli, João Gabriel S. Souza, Valentim A. R. Barão
Electrophoretic deposition is another physical method developed based on the particles’ movement under an electric field. Charged particles can be deposited on a metal substrate to create thin or thick films. The process is done in two steps. The first consists of creating an electrical field attracting particles of the opposite charge; in the second step, the particles accumulate and can form a compact film (Figure 3. A4). Then, heat treatment can be applied to enhance the film properties [174,175], resulting in a more compact and dense film with superior mechanical and corrosion properties. This technique is often used to produce bioactive glass, chitosan, and other polymeric coatings since the process is simple, controllable, and produces high-quality surfaces (Figure 3. B4) [176,177].