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Luminescent, Film, and Cryogenic Detectors
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
TLD-100 dosimeters are sensitive to charged particles, gamma rays, and neutrons. Gamma rays excite primary electrons in the material through the photoelectric effect, Compton scattering, or pair production. These energetic electrons excite secondary electrons in the material through Coulombic scattering. It is unlikely that energetic electrons deposit all of their energy in a small TLD chip before reaching the detector boundaries; hence, usually only a fraction of the incident energy is measured. The same is true for energetic beta particles. However, dosimetry is based on the amount of ionization produced in the body, primarily body tissue, and cavity theory attempts to correct for these energy losses.5
Surface Phenomena
Published in Pramod K. Naik, Vacuum, 2018
Secondary electrons are generated by neutrals, ions, electrons, or photons with sufficiently high energy. Photoelectrons also can be considered as secondary electrons. When an ion or an excited atom approaches a metal surface, neutralization of the ion may occur and de-excitation or resonance ionization of the excited atom may take place. It is evident from the experimental data that electronic transitions involved in these processes are almost independent of the kinetic energy of the incident particle and are governed by its potential energy of excitation. The electronic transitions 52,53 include: Resonance neutralization Resonance ionization Auger de-excitation Auger neutralization
Radiation Sterilization
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Barry P. Fairand, Dusan Razem, Karl Hemmerich
At intermediate photon energies that characterize the gamma ray and X-ray (Bremsstrahlung) sources of radiation used in the radiation sterilization process, the dominant channel for interaction of the photons with the orbital electrons occurs via a process called Compton inelastic scattering. This method of energy transfer is named after the person that first described the quantum mechanical relationships governing the scattering process [2]. A photon undergoing Compton scattering transfers part of its energy to the orbital electron. The amount of energy transferred to the electron will depend on the quantum mechanical relationships governing the scattering event but is usually sufficient to not only ionize the atom but also leave the electron with significant kinetic energy to continue the ionization process. In fact, the most probable Compton scattering event is a backscatter of the photon, which transfers maximum energy to the electron. For gamma rays emitted by a cobalt-60 source, a backscattered photon will deliver about 1 MeV to the orbital electron. These high-energy electrons are referred to as primary electrons. The scattered photon continues to undergo scattering events and generate additional primary electrons until its energy is dissipated. The primary electrons have sufficient energy to ionize other atoms via an electron–electron inelastic scattering process. A whole cascade of secondary electrons can be produced in this manner. From a numerical standpoint, it is primarily these secondary electrons that are the source of the physical and chemical events that lead to the radiation-induced changes in materials and sterilization of the medical device/drug product. The photon functions as an initiator of the process that leads to radiation sterilization throughout the bulk of the medical device/drug product.
Radiosensitization with iron nanoparticles under 10–800 Ry photon irradiation: Monte Carlo simulation of particle-to-medium energy transfer
Published in Radiation Effects and Defects in Solids, 2022
Alexander P. Chaynikov, Andrei G. Kochur, Victor A. Yavna
We performed a detailed MC simulation of energy transformation and transfer processes in iron NPs under photon irradiation. The MC algorithm considers the processes of the cascade decay of inner-shell vacancies. The simulations showed that the NPs re-emit most of the energy of an absorbed photon into the surrounding medium with cascade-produced secondary photons and electrons. Most of the energy is transferred to the medium by high-energy secondary electrons capable of ionizing the medium’s atoms. However, when incident photon energy is above the Fe1s-ionization threshold, 2p-1s and 3p-1s photons produced at the first step of the Fe1s-vacancy cascade also contribute noticeably to the energy carried away from the nanoparticle. Low-energy electrons are born in significant quantities due to asymmetric energy sharing by two final state electrons in electron impact ionization. They leave NPs in great quantities, especially in the case of large NPs. This leads to the formation of high positive charges on NPs, and to the appearance of strong electric fields near their surfaces. As the time of complete relaxation of the NP after ionization of its atom, i.e., the time during which the electric field is formed, is much shorter than the time needed for the screening of the field, the NPs’ electric field may interfere with the DNA repair processes discovered earlier, and thus become an additional factor of radiosensitization.
Variation of Internal Doses Caused by Differences in Physical Characteristics between the Average Japanese and the ICRP’s Reference Man Which Is Based on the Standard Data of Caucasians in the Dosimetric Methodology in Conformity to the 2007 Recommendations
Published in Journal of Nuclear Science and Technology, 2022
Kentaro Manabe, Kaoru Sato, Fumiaki Takahashi
Additional radiation transport calculation was executed to make the Japanese SAF dataset consistent with the current procedure for calculating Φ(T←Other) (Equation (2)). Yellow marrow is one of the assigned organs and tissues where radioactivity is distributed in the current systemic models. The others are not assigned as specific organs nor tissues in any systemic models [3–5]. Therefore, we defined ‘residual’ tissues as a source region by combining the organs and tissues other than yellow marrow and evaluated the SAFs of which the source region is residual tissues using MCNPX 2.6.0 [20] under the same calculation conditions as the existing SAF data [18,19]. The libraries el03 [25] and mcplib04 [26] were applied as cross-sectional data for electrons and photons, respectively. The lower cutoff energy was set to 1 keV with consideration of the voxel size of the Japanese phantoms. Secondary electrons produced by interactions of primary photons with tissue materials were also transported. The added SAFs enabled the calculation of Φ(T←Other) using Equation (2).
Experimental investigations of particle formation from propellant and solvent droplets using a monodisperse spray dryer
Published in Aerosol Science and Technology, 2018
James W. Ivey, Pallavi Bhambri, Tanya K. Church, David A. Lewis, Reinhard Vehring
Collected particle samples were examined using field emission scanning electron microscopy (FE-SEM). Samples were first coated in gold by sputter deposition (Desk II, Denton Vacuum, Moorestown, NJ, USA) for 120 s at 15–20 mA then imaged using FE-SEM (Sigma FE-SEM, Zeiss, Jena, Germany). A 30 µm aperture was employed, and accelerating voltage was 2–5 kV. Imaging was achieved by detection of secondary electrons using the out-of-lens detector. Selected samples were analyzed by sectioning particles with a focused beam of gallium ions (30 kV accelerating voltage, 50 pA beam current, 40 µm aperture) followed by imaging with a beam of helium ions (30 kV accelerating voltage, 1 pA beam current) (Orion NanoFab, Zeiss, Jena, Germany). Selected micrographs were analyzed to evaluate particle size distributions. Particle edges were delineated using circles for spheroidal particles (MATLAB R2014 a, Mathworks, Natik, MA, USA). The edges of collapsed spheroidal particles and irregular crystalline particles were delineated with freehand tracing and polygons, respectively (ImageJ, NIH, Bethesda, MD, USA). For each particle, a projected area equivalent diameter (Hinds 1999) was then computed based on the area enclosed by the bounding shape :