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
The average ionization potential, I, is a weighted mean value over the atoms all excitation and ionization potentials and is therefore much higher than the smallest energy that is required to make an ionization. The value is determined from measurements of the stopping power or the range of heavy particles. The magnitude is approximately eV. The stopping power depends on the logarithm of I, as can be seen from Eq. 3.51; the precise value of I is not that critical. The two terms that include the relative velocity, , are only important for particles with speeds close to c.
General Radiobiology Refresher
Published in Loredana G. Marcu, Iuliana Toma-Dasu, Alexandru Dasu, Claes Mercke, Radiotherapy and Clinical Radiobiology of Head and Neck Cancer, 2018
Loredana G. Marcu, Iuliana Toma-Dasu, Alexandru Dasu, Claes Mercke
The ionisation potential of radiation is another factor that modulates the biological effects. This potential is quantified as a linear energy transfer (LET) that gives a measure of the energy transferred by the particles per unit length of their track. For directly ionising particles, the LET is the stopping power restricted only to transfers that could be considered local, in the proximity of the DNA molecule. For indirectly ionising radiation, it represents an average of the restricted stopping power of the secondary particles created from interactions with the medium. However, due to the stochastic character of the interaction of these particles, one could distinguish between track average LET and energy average LET, depending on how the average has been calculated. This distinction however is most prominent for particles with high LET that have a large variance of the energy deposition events and to a lesser extent for low LET radiation. Photons and electrons that are the most used radiation modalities in modern radiotherapy are regarded as low LET radiation, while neutrons and some of the ions used for radiotherapy are regarded as high LET radiation. It should be noted however that there is no threshold for the transition from low to high LET and that even for the same type of radiation the LET varies with its energy and even the medium, in the same manner as the variation of the stopping power of the charged particles involved.
Dictionary
Published in Mario P. Iturralde, Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990
Ionization potential. The energy (in electron volts) which is required to remove a particular electron from an atom is measured by its ionization potential (in volts). For the outermost electrons in almost all atoms the ionization potentials lie between 5 and 20 V, while those of the most tightly bound inner electrons in the heaviest atoms approach 100 kV.
Risk assessment of heterogeneous TiO2-based engineered nanoparticles (NPs): a QSTR approach using simple periodic table based descriptors
Published in Nanotoxicology, 2019
Joyita Roy, Probir Kumar Ojha, Kunal Roy
Ionization potential is the difference of energy between the ground state and state of ionization, and this amount of energy is required to completely remove the loosely attached electrons. The 2nd ionization potential is greater than 1st ionization potential and depends upon the size, charge and the type of electrons removed from outer shell of the atom. Ionization potential also determines the electronegativity and electron affinity of an atom. The low ionization energy of an atom (the energy required to remove the outer shell electron) indicates that the atom can easily lose its outer shell electron and has fewer tendencies to gain electrons. Thus, it clearly indicates that the atoms with high ionization potential will have high electronegativity. The electronegativity is responsible for the catalytic property of the cationic form of the metal and therefore increases the cytotoxicity. The positive regression coefficient of this descriptor indicated that an atom with higher 2nd ionization potential increases the cytotoxicity of the hamster ovary cell and vice versa. As for example, the nanoparticles 6.5Ag_0.5Pt and 6.5Ag are highly toxic (toxicity values are 5.8 and 5.88 respectively) towards the cytotoxicity to hamster ovary cell due to their higher range of 2nd ionization potential (14350.5 and 13455 respectively), whereas in case of nanoparticles 0.25Pt and 0.1Au, the cytotoxicity (4.56 and 4.67 respectively) decreases with its 2nd ionization potential (447.75 and 198 kJ/mol respectively).
Nanocarrier for levodopa Parkinson therapeutic drug; comprehensive benserazide analysis
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Mehdi Yoosefian, Elham Rahmanifar, Nazanin Etminan
Quantum molecular DFT based descriptors for Bz/c-CNT and its constituents are calculated and compared in Table 7. Gas phase geometry of BZ has a HOMO-LUMO energy gap of 4.91 eV. On the other hand, c-CNT found to be more reactive than the (5,5) SWCNT counterpart. Although in BZ adsorbed onto c-CNT the change in chemical hardness values are not very dramatic but the most stable conformer shows the highest stability. The chemical potential of conformer 3 is higher suggesting it to be more reactive. Lowering the electrophilicity index of mentioned conformer leads to behaves as a better nucleophile. These results support with the calculated values of ionization potential and electron affinity values.