China
Africa
Explore chapters and articles related to this topic
Basics of Radiation Interactions in Matter
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
There are also some differences in the naming of photons. Gamma rays are those photons emitted as a result of the decay of a nucleus, and which therefore originate from the nucleus. X-rays that are emitted as a result of energy loss when electrons, accelerated in the vicinity of the atomic nucleus, are named ‘bremsstrahlung photons’ (sometimes also ‘braking radiation’). When a positron is close to an electron, and both particles are close to rest, a transformation of the two electron masses to energy in the form of electromagnetic radiation is possible with the result of two annihilation photons. A vacancy in an electron shell, caused by, for example, photoelectric absorption of an incoming photon, is called a ‘characteristic X-ray’ because the energies of these emitted X-ray photons are characteristic of the energy levels of the different electron shells and thus of the element. It is therefore recommended to follow these naming conventions because they provide information about the underlying interaction process.
Kilovoltage X-Ray Units
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
The bremsstrahlung energy spectrum emerging from the target shows a continuous distribution of energies with characteristic x-rays at discrete energies superimposed on this. In the absence of any filtration, the calculated energy spectrum emerging from a thick target will be a straight line given by the following equation (Johns and Cunningham 1983):
Diagnostic Imaging Using X-rays
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
Debbie Peet, Richard Farley, Elizabeth Davies
When these fast-moving electrons collide with a dense target metal (e.g. tungsten), they are rapidly slowed down, releasing their energy. Most of the kinetic energy from the electrons is converted to heat with only a small fraction being converted into X-rays. These X-rays are known as Bremsstrahlung, which is German for “braking radiation”. To prevent the anode from overheating, it is rotated at very high speed to help dissipate the heat. The maximum photon energy achieved is equal to the maximum kinetic energy of the electrons, driven by the peak voltage between the anode and cathode (kVp; Figure 4.2). The flux of electrons, and therefore the intensity of X-rays, is determined by the cathode filament current (typically several amps are needed). The target material is usually tungsten, but other materials are also used for specialist imaging applications, such as breast imaging (mammography). Characteristic X-rays are also produced at an energy dependent on the target material.
9th international symposium on physical, molecular, cellular, and medical aspects of Auger processes: preface
Published in International Journal of Radiation Biology, 2023
Katherine A Vallis, Roger F. Martin, Nadia Falzone
Removal of an inner orbital electron through the photoelectric effect, electron capture, or internal conversion leads to a vacancy which is then filled by a cascade of electron transitions from the outer shells. These transitions are accompanied by the emission of low energy ‘Auger’ electrons or characteristic X-rays. Auger electrons have low energy (<25 keV), have a short track length and are densely ionizing. As a result, the absorbed radiation dose they deposit in biological material is extremely high but restricted to a nanoscale volume (a few nm3) around the decay site. These qualities mean that Auger electron emitting radionuclides are suited to the ultra-precise delivery of radiation to individual cells, organelles or even to specific molecular targets, and so hold promise as oncologic therapeutic agents.
Advancements in the use of Auger electrons in science and medicine during the period 2015–2019
Published in International Journal of Radiation Biology, 2023
The removal of an inner shell electron from an atom leaves the atom in an excited state. Atomic relaxation to the ground state occurs via radiative and nonradiative processes within the atom containing the original vacancy, and via processes that take place in neighboring atoms. Radiative processes are those that emit photons such as characteristic X-rays. Nonradiative processes emit Auger electrons, Coster-Kronig (CK) electrons, and super-CK electrons. These categories of electrons, often collectively referred to simply as Auger electrons, are characterized by the shells and subshells involved with the transition. Radiative processes dominate K-shell transitions, whereas nonradiative processes dominate when the vacancy is in the L-shell and above. Nevertheless, the vacancy is filled rapidly which leads to the creation of new vacancies in higher subshells forming a cascade of atomic transitions that emit a shower of low energy Auger electrons and characteristic X-rays.
Scanning electron microscopy in analysis of urinary stones
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2019
Martin Racek, Jaroslav Racek, Ivana Hupáková
Chemical characteristics of materials including kidney stones can be also achieved with X-ray spectroscopy analytical methods. The use of these methods requires primary irradiation of the sample, which leads to ejection of electrons from the sample atoms. The resulting unstable state leads to an effect where the hole is filled by an electron from a higher orbital. The difference of the energy is balanced by a release of a photon with energy/wavelength characteristic for a given element. The characteristic X-rays emission can be reached in various ways, which is determinative for each method. The sample may be irradiated by high-energy protons (PIXE [47,48]), high-energy electrons (coupled with SEM, [29,35,38]) or primary X-rays (XRF [47–50]). The emitted X-rays can then be characterized based on their energy (energy-dispersive spectroscopy [EDS]) or wavelength (wavelength-dispersive spectroscopy [WDS]).