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X-ray Interactions in Matter
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
This process will meet the parameters set out in the last paragraph above. It occurs when the energy of the incoming photon is considerably greater than the binding energy of the electron involved. In the case of the Compton scattering process, the photon energy is so much greater than the electron binding energy that some texts describe the electron as being a ‘free’ electron. This somewhat confusing term can lead you to think that the electron is not bound into an atom at all. This is not the case, it is a term which is used to try and indicate the mega-mismatch between the two energies involved i.e. the X-ray photon and the weekly-bound electron.
Particles and Radiation
Published in Rob Appleby, Graeme Burt, James Clarke, Hywel Owen, The Science and Technology of Particle Accelerators, 2020
Rob Appleby, Graeme Burt, James Clarke, Hywel Owen
We have seen that in ordinary Compton scattering – where the electron is initially stationary – that the scattered photon always reduces in energy. Inverse Compton scattering is the situation where the electron is moving sufficiently fast that a collision may cause the photon to increase in energy. For this to occur, the electron typically must be moving relativistically with . We will see that an incident photon can be scattered to a much larger outgoing energy.
Photon Beams, Dose, and Kerma
Published in Eric Ford, Primer on Radiation Oncology Physics, 2020
Kerma is the kinetic energy released when a photon enters material. Recall that at therapy energies this usually occurs through the Compton scattering process (Section 5.2.1) where some of the energy of the photon is given to an electron in the form of kinetic energy. The photon can undergo further Compton scattering, and the electron can make photons of its own that then Compton scatter. All this happens in a cascading process, and energy is released in the form of moving charged particles, i.e. electrons (Figure 5.2.2). This is kerma.
Monte Carlo-based calculation of nano-scale dose enhancement factor and relative biological effectiveness in using different nanoparticles as a radiosensitizer
Published in International Journal of Radiation Biology, 2021
Mostafa Robatjazi, Hamid Reza Baghani, Atefeh Rostami, Ali Pashazadeh
Although employing NPs as a radiosensitizer in high-energy X-ray radiotherapy is a useful approach for more efficient tumor cell killing, NP-assisted low-energy X-ray radiotherapy can result in more remarkable dose enhancement during the treatment. In this way, the results of the MC-based study by Kakade and Sharma (2015) demonstrated that the obtained dose enhancement factor (DEF) at the keV photon energy region is about 188% higher than that attained at MeV one when AuNPs are used during the irradiation. This fact is mainly linked to the large cross-sections of photoelectric interactions at low energy X-ray region, while the Compton scattering is the prevailing interaction at the high energy one. Therefore, the employed NPs during the low energy X-ray radiotherapy can act as promising and reliable radiosensitizers for dose enhancement purposes.
Experimental assessment on feasibility of computed tomography-based thermometry for radiofrequency ablation on tissue equivalent polyacrylamide phantom
Published in International Journal of Hyperthermia, 2019
Daryl Tan, Nurul Ashikin Mohamad, Yin How Wong, Chai Hong Yeong, Peng Loon Cheah, Norshazriman Sulaiman, Basri Johan Jeet Abdullah, Mohd Kamil Fabell, Kok Sing Lim
The idea of CT number dependence on temperature was conceived more than three decades ago where a temperature-dependent shift of CT number was observed in water and biological tissues. The CT number is a measurement of the ability of a material to attenuate X-ray photons and generally expressed in dimensionless Hounsfield Units (HU) using the following equation: water is the linear X-ray attenuation coefficient of water while μobject is the average linear attenuation coefficient of the material. X-ray attenuation in CT scan is mainly due to Compton scattering effects. The probability of Compton interaction is proportional to the physical density of the material/tissues. Therefore, the change in material/tissue density with temperature due to thermal expansion indicates that there is a direct relationship between temperature and variation of CT number.
Imaging-based internal body temperature measurements: The journal Temperature toolbox
Published in Temperature, 2020
Juho Raiko, Kalle Koskensalo, Teija Sainio
Temperature dependence of water and biological tissue sample HU values was first described in 1979 by Bydder et al. [73]. In CT imaging, attenuation is mostly due to Compton scattering. The probability of Compton interaction increases in relation to the effective electron density of the imaged tissue. Increase in tissue temperature results in thermal expansion of the tissue further resulting in decreased electron density and decreased attenuation. Thus, an increase in tissue temperature results in lower CT number in the examined tissue (see Figure 5). The phenomenon can be formulated as follows: