China
Africa
Explore chapters and articles related to this topic
Electron Beam Processing of Rubber
Published in Anil K. Bhowmick, Current Topics in ELASTOMERS RESEARCH, 2008
Rajatendu Sengupta, Indranil Banik, Papiya Sen Majumder, V. Vijayabaskar, Anil K. Bhowmick
High-energy radiation interacts with a material by three principal mechanisms [25–28]: Photoelectric effect: By which a photon is absorbed and an orbital electron, having the energy of the incident radiation minus the binding energy, is ejected.Compton scattering: By which an electron is ejected, while the photon (of reduced energy) is scattered.Pair production (above 1.022 MeV): By which a positron–electron pair is produced, and where subsequent annihilation of the positron generates γ-rays of ≈0.511 MeV which may further interact by the first two mechanisms.
High-Energy (X-Ray and γ-Ray) Photon Interactions with Matter
Published in Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull, X-Ray Imaging, 2016
Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull
where E is energy (ergs), m is mass (g), and c is velocity of light (cm/s). If we let m be the rest mass of the electron, mβ− be 9.11 × 10−2 g, and c be 3 × 1010 cm/s, and insert the conversion factor 1.6 × 10−6 erg/MeV, the equation gives the energy equivalent of the electron, 0.51 MeV. It follows that the threshold photon energy for pair production is 1.02 MeV since the electron and positron have the same mass. Pair production dominates attenuation for chemical elements iron through uranium at energies greater than 8 MeV (see Figure 5.10).
Photon Beam Physics
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
Solution:The Compton effect (incoherent scattering) represents a photon interaction with an essentially ‘free and stationary’ orbital electron. The incident photon energy is much larger than the binding energy of the orbital electron. The incident photon loses part of its energy to the recoil (Compton) electron and is scattered as photon with lower energy through a scattering angle. Two factors that influence the probability of Compton effect are the energy of incident photon and electron density of interacting medium.In the photoelectric effect the photon interacts with a tightly bound orbital electron of an attenuator and is completely absorbed, while the orbital electron is ejected from the atom as a photoelectron. Two factors that influence the probability of photoelectric effect are the energy of incident photon and the atomic number of interacting medium.When the energy of an incident photon is greater than the rest mass energy of an electron and a positron (2m0c2 = 1.022 MeV), the photon may be absorbed through the mechanism of pair production. Here, the photon passes very close to the nucleus, and its energy is used to create an electron-positron pair. The excess energy is shared between the electron and positron as kinetic energy. These two particles may collide through a process known as annihilation and converted to two photons with equal energy of 511 keV. Two factors that influence the probability of pair production are the energy of incident photon and the atomic number of interacting medium.
Enhancing radiographic imaging of cementitious materials in composite structures with photon attenuating inclusions
Published in Research in Nondestructive Evaluation, 2019
Wesley J. Keller, Stephen Pessiki
At higher energy levels, such as those employed by MeV X-ray betatrons (1–9 MeV), attenuation in all materials is relatively low and mainly due to Compton scattering, i.e., the influence of photoelectric absorption is significantly reduced. For high atomic number elements (e.g., barium), however, a second form of attenuation in this higher energy region of the emission spectrum known as pair production becomes significant. The probability of pair production increases with photon energy and atomic number of the element interacting with the photon. As a result, high atomic number elements exhibit significantly different attenuation characteristics below or near the pair production threshold energy of 1.02 MeV than they do at energy levels well above this threshold. As a result, it is believed that this change in attenuation around the pair production threshold may be useful in identifying and quantifying these materials (e.g., PAI grouts) through dual energy radiography, although this topic is not addressed in the present study.
Shielding Analysis for a Moderated Low-Enriched-Uranium–Fueled Kilopower Reactor
Published in Nuclear Technology, 2022
Jeffrey C. King, Leonardo de Holanda Mencarini
In photoelectric absorption, a gamma photon of energy greater than the binding energy of an orbital electron interacts with a target atom, with all the photon energy being transferred to an orbital electron. The electron is ejected from the atom, and the excess energy becomes the kinetic energy of the electron. Compton scattering results from the interaction between the gamma photon and an orbital electron. The direction vector of the gamma photon is changed based on the amount of photon energy absorbed by the electron. In pair production, the photon interacts to annihilate the gamma photon to generate an electron-positron pair. The mass of the electron-positron pair is equivalent to 1.02 MeV, establishing a minimum photon energy for this event. Since the common gamma-ray interactions involve electrons, gamma shields most often consist of high-density, high-atomic-number elements such as lead, tungsten, or depleted uranium. Unfortunately, in the presence of high-energy neutrons, these elements can produce significant amounts of additional gamma rays from inelastic scattering reactions. Since fission neutrons are generated with high energies (>1 MeV), layered shields consisting of alternating layers of neutron- and gamma-absorbing materials become important to maximize radiation attenuation while minimizing the mass of the shield. This becomes particularly important for high-power space nuclear reactors. In lower-power reactors, such as Kilopower Reactor Using Stirling TechnologY (KRUSTY), it is potentially possible to omit the high-density gamma shielding material.13 Thus, the present research considers a single-layer shield consisting solely of neutron moderators and absorbers.