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Basic Atomic and Nuclear Physics
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Gudrun Alm Carlsson, Michael Ljungberg
The de-excitation of the nucleus does not always occur because of the transmission of γ-radiation. The energy released at the transition between two energy states can instead be transferred to an electron in one of the surrounding shells (Figure 2.8). The electron is hereby released from the atomic shell with a kinetic energy equal to the energy released at the nuclear transformation minus the electron’s binding energy in the atomic shell. This type of process is called internal conversion (I.C). For such a process to be energetically possible, the energy released at the nuclear decay must be greater than the binding energy of the electron. The I.C. is an important process in de-excitation of high-Z nuclides, when the energy released at the nuclear transition is immediately above the binding energy of an electron in the atomic scale and then the nucleus transition is isomeric.
Physics of Radiation Biology
Published in Kedar N. Prasad, Handbook of RADIOBIOLOGY, 2020
In some disintegrations, the excited nuclei may get rid of its excess energy by internal conversion. In this process, γ-rays from the nucleus interact with one of its own inner electrons, which is ejected with a kinetic energy equal to the energy of the γ-ray minus the binding energy of electrons. During internal conversion, no γ-ray is emitted; however, characteristic X-radiation and Auger electrons are produced when the ejected conversion electron is replaced. The probability of internal conversion increases rapidly with atomic number and with the lifetime of the excited state of the nucleus.
Nuclear Physics Fundamentals Milorad Mladjenovic
Published in Frank Helus, Lelio G. Colombetti, Radionuclides Production, 2019
Internal conversion competes with photon emission, and, in a sense, these are two complementary processes. The probability of internal conversion increases with increasing Z and decreasing E, being negligible for light nuclei, but almost always occurring in heavy nuclei, especially at low transition energies.
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
Atomic vacancies that lead to Auger and ICD processes are created by several mechanisms. One mechanism that creates an inner atomic shell vacancy is the photoelectric effect. The Auger electrons that are emitted following the photoelectric effect were observed by Pierre Auger when he irradiated a cloud chamber with X-rays (Auger 1923). Radionuclides undergoing internal conversion (IC) transitions also create inner atomic shell vacancies, as do radionuclides that decay by electron capture (EC). The shower of low energy electrons that follow was seen by Meitner when she was conducting experiments on radioactive decay (Meitner 1923). The stochastic nature of the atomic and molecular electronic relaxation process results in different yields and energies of electrons for each initial vacancy created. Most of these electrons have very low energies (∼20–500 eV) which have extremely short ranges in water (∼1–10 nm). Biological molecules near the Auger cascade are impacted by the direct effects of electron irradiation as well as indirect effects caused by radical species that are produced during the radiolysis of water by these electrons (Figure 2) (Wright et al. 1990). Other physical mechanisms such as Coulomb explosion, caused by extremely rapid charge neutralization of highly ionized atoms, can cause damage to the molecule in which electronic vacancies are created (Pomplun and Sutmann 2004).
Assessing the impact of low level laser therapy (LLLT) on biological systems: a review
Published in International Journal of Radiation Biology, 2019
Ruwaidah A. Mussttaf, David F. L. Jenkins, Awadhesh N. Jha
This is the most common pathway that occurs and is called internal conversion, the excited singlet state of a chromophore is transported from a higher to a lower electronic state. This transition takes place without photons emitting, known as non-radiative decay (Hamblin and Demidova 2006). The energy of the electronically excited state is coupled to rotational and vibrational modes of the molecule. Thus, this interaction increases the kinetic energy of the molecule, such that the excitation energy is transformed into heat. This process would not be expected to cause chemical changes to the molecule (Smith 1991).