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Scintillation Detectors
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
There are two major types of photocathodes – multialkali (Na2KSb) and bialkali (K2CsSb). In NEA-dynodes (negative electron affinity) the lifetime of the created electrons is longer, which means a greater probability for escape from the surface before losing kinetic energy. The multiplication factor for NEA-dynodes is around 40–60 as compared with around 10 for normal dynode materials. The stronger emission of electrons is also important with respect to time resolution. The more abundant number of electrons means less relative variance and thus better-defined timing with less uncertainty. Normally the scintillator decay time determines the time resolution, but for fast scintillators it is the PM tube. Total time from photocathode to pulse out is about 50 ns.
The oxygen effect and therapeutic approaches to tumour hypoxia
Published in Michael C. Joiner, Albert J. van der Kogel, Basic Clinical Radiobiology, 2018
Michael R. Horsman, J. Martin Brown, Albert J. van der Kogel, Bradly G. Wouters, Jens Overgaard
The concept of chemical radiosensitization of hypoxic cells was introduced by Adams and Cooke (2) when they showed that certain compounds were able to mimic oxygen and thus enhance radiation damage. They also demonstrated that the efficiency of sensitization was directly related to the electron affinity of the compounds. It was postulated that such agents would diffuse out of the tumour blood supply and unlike oxygen, which is rapidly metabolized by tumour cells, these compounds would be able to diffuse further, reach the more distant hypoxic cells and thus sensitize them. Since these drugs mimic the sensitizing effect of oxygen, they would not be expected to increase the radiation response of well-oxygenated cells in surrounding normal tissues; radiation tolerance should therefore not be compromised.
Biomedical Accelerator Mass Spectrometry
Published in Graham Lappin, Simon Temple, Radiotracers in Drug Development, 2006
Although AMS, in the drug development area, has been used mostly to quantify 14C, the technique is by no means limited to this isotope. An element should conform to the following criteria if it is to be analyzed by AMS: Since AMS is an isotope ratio technique, at least two isotopes for any given element are required, one of which should be rare. The natural abundance of the rare isotope determines the signal-to-noise ratio, and hence the sensitivity of the measurement. It is for this reason that 14C is suitable for AMS and 13C (natural abundance, 1.1%) is not. Some elements only have one stable isotope (Be, F, Na, Al, P, Sc, Mn, Co, As, Y, Nb, Rh, I, Cs, Pr, Pm, Tb, Ho, Tm, Au, and Bi), and therefore by definition their other (radio-)isotopes are rare or nonexistent in nature. This does not mean they are necessarily useful in AMS, as the radioisotope must have a usable half-life.Elements with a low electron affinity (e.g., N, Mn, Pr, Pm, and Ho) do not readily form negative ions. These elements can still be measured by AMS, but analysis is more complicated and is based on molecular ion beams (e.g., MnH).Since samples have to be prepared for AMS analysis, isotopes with short half-lives are impractical.
Chemical radiosensitizers: the Journal history
Published in International Journal of Radiation Biology, 2019
The next radiosensitizer paper and the first in vitro one published by the Journal was the 1964 paper by Bianchi et al. This paper reported that iodoacetic acid and ‘more or less related compounds’ (including N-ethylmaleimide, NEM) sensitized red blood cells to irradiation in vitro. Many further papers (∼20) on NEM and iodoacetates followed in the Journal particularly over the rest of the decade (Bianchi et al. 1964; Moroson and Spielman 1966; Bridges and Munson 1967; Grigoresco et al. 1967; Moroson and Furlan 1968; Adams and Cooke 1969; Kada 1969; Mullenger and Ormerod 1969; Ward et al. 1969). The mechanism of action of NEM and related compounds was never firmly established; one theory was that it was due to their thiol-binding ability (Moroson and Spielman 1966), but another related to what we would now call electron-affinity (Adams and Dewey 1963). These compounds disappear from the pages of the Journal after the early 80s because better radiosensitizers were found that had much less toxicity (Shenoy and Singh 1985). However, the research on NEM has a direct historical and scientific connection to the development of modern hypoxic cell sensitizers (Scott and Sturrock 1968).
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).
JM-20 protects memory acquisition and consolidation on scopolamine model of cognitive impairment
Published in Neurological Research, 2019
Maylin Wong-Guerra, Javier Jiménez-Martin, Luis Arturo Fonseca-Fonseca, Jeney Ramírez-Sánchez, Yanay Montano-Peguero, Joao Batista Rocha, Fernanda D´Avila, Adriano M. de Assis, Diogo Onofre Souza, Gilberto L. Pardo-Andreu, Roberto Menéndez-Soto del Valle, Guillermo Aparicio Lopez, Odalys Valdés Martínez, Nelson Merino García, Abel Mondelo-Rodríguez, Alejandro Saúl Padrón-Yaquis, Yanier Nuñez-Figueredo
Here we observed that 8 mg/kg JM-20 diminished the MDA levels while increased T-SH levels, maintaining normal activities of SOD and CAT enzymes, therefore evidencing strong antioxidant protection against scopolamine. Consequently, we postulate that JM-20 also inhibited the AChE and protected memory by its antioxidant properties. This suggestion is also supported by an antioxidant profile of JM-20 at mitochondrial level: 1) It inhibited H2O2 generation on rat brain mitochondria and synaptosomes, 2) displayed a cathodic reduction peak at −0.71 V, which is close to that of oxygen (−0.8 V) indicating high electron affinity, and 3) inhibited uncoupled respiration [5,7]. Hence, JM-20 may also act by blocking the generation of reactive species and trapping electrons escaping from the electron transport chain mitochondrial, a potential mechanism to prevent oxidative damage.