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Measurement of Giant Resonances
Published in P. F. Bortignon, A. Bracco, R. A. Broglia, Giant Resonances, 2019
P. F. Bortignon, A. Bracco, R. A. Broglia
Another useful quantity in the study of the decay of the compound nucleus is the branching ratio for high-energy γ-decay. At zero temperature, the γ-width for decay of a state J1 to a state J2 summed over the magnetic states M1 is given by Γγ = 5.2£γ (MeV2) NZ/A (eV). Since the total width of the GDR based on the ground state displays values (cf. Fig. 2.5(c)) ranging from 4 MeV (spherical nuclei) to 8 MeV (deformed nuclei), the ground state γ-branching-ratios Γγ/Γ are in the range 10-3 to 10-2. The γ-branching ratio for the decay to excited states (hot nuclei), can be deduced integrating the γ-decay strength for the first step of the γ-decay cascade and calculating the total width for the decay. These values are in general smaller (within an order of magnitude) than those corresponding to the T = 0 MeV decay.
Radioisotope Production and Application
Published in Paul R. Bolton, Katia Parodi, Jörg Schreiber, Applications of Laser-Driven Particle Acceleration, 2018
In addition, it is important to remember that an unstable nucleus can decay into one or more channels. If decay occurs through several channels, we refer to the branching ratio for one channel as the percentage of decays occurring that way. For example, one very long-lived isotope (with about 1.25 gigayears half-life) that we have in our body is 40K. It decays in two different channels: one is electron capture (EC; i.e. capture of an inner electron by the nucleus), with a branching ratio of 10.7%, forming 40Ar; and the other is β− (electron) decay, yielding 40Ca, with a branching ratio of 89.3%. For a radioisotope to be useful in medicine, we need to have a complete map of the different decay channels and branching ratios, up to the percent level or so. Some of the decay channels are applied for imaging or treatments. The rest of the decay channels represent dose that the patient receives without any benefit.
Physics of X-Ray and γ-Ray Sources
Published in Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull, X-Ray Imaging, 2016
Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull
For a 22Na atom, known as the radioactive parent, the radioactive decay is by either EC or the emission of a positron (see Figure 4.9). The branching ratio is 0.90 β+ and 0.10 EC, given that the branching ratio is the number of decays of a particular type divided by the total number of decays. In either case, in essence, a proton is converted into a neutron, and the daughter atom becomes 22Ne. The daughter atom is in a neutron-excited state, and the neutron transitions (decays) to the ground state via emission of a 1.274 MeV γ-ray. In addition to this γ-ray, the β+ generates annihilation photons and Ne characteristic x-rays Kα1 and Kα2 both of 848.6 eV (Thompson et al. 2001). A representative 22Na γ-ray/x-ray energy spectrum is shown in Figure 4.12. 57Co decays by EC, as shown in Figure 4.9, and this decay generates γ-rays and x-rays. 60Co and 137Cs decay by β−, as shown in Figure 4.9. These radioactive isotopes emit an electron from the nucleus, and in so doing, a neutron is converted to a proton. 60Co results in a proton in a 2.505 MeV excited energy level, which subsequently decays by emission of two γ-rays, 1.173 and 1.332 MeV, of equal intensity (see Figure 4.10). 137Cs decays to the ground state and a 0.662 MeV excited state of Ba (see Figure 4.9). A representative 137Cs γ-ray/x-ray energy spectrum is shown in Figure 4.11.
Theoretical Study of Intramolecular H-Migration Reactions of Peroxyl Radicals of JP-10 (Exo-Tetrahydrodicyclopentadiene)
Published in Combustion Science and Technology, 2023
Jie Min, NingXin Tan, ZeRong Li, JingBo Wang
L is the reactant, and B1, B2, ……, Bn are products. The rate coefficients of R1, R2, ……, Rn reactions are k1, k2, …., kn, respectively. The branching ratio of Ri reaction is defined as: . The larger the branching ratio of a reaction is, the more competitive this reaction is. In our study, six reactants will produce 33 isomer products. If the subsequent reactions of these products are added in the oxidation mechanism of JP-10 at low temperature, the mechanism will be too large to be adopted for CFD. Therefore, the isomer lumping method was used to lump reactions with the same reactant (Lu and Law 2008). Here, the products B1, B2 ……Bn are classified as a single product B. The concentration of B is a sum of concentrations of Bi, . Therefore, for the lumped reaction , the rate coefficient is lumped as . Because the above reactions have the same reactant and similar reaction paths, the weight ratio of each product Bi can be represented by (Pitzer and Gwinn 1942): . The rate coefficients of lumped reactions were fitted to the modified Arrhenius equation.
On the Use of Graph Theory to Interpret the Output Results from a Monte-Carlo Depletion Code
Published in Nuclear Science and Engineering, 2021
The method just built is valid but does not really address the issue raised in the beginning of this section, which was to identify, for a given nuclide , the initial isotope from which it most likely originates. To answer this question, one has to follow the paths backward and thus associate with each path a notion of ingoing branching ratio. This notion can be defined in a simple manner, by the ratio of the rate of the reaction in which one is interested (i.e., the reaction on the path under consideration) to the sum of the reaction rates ending on the nuclide. Multiplying the ingoing branching ratios on each path from to , one obtains a measure whose interpretation can be thought of as the likelihood of a nuclide to originate from the initial isotope .
Cold temperatures invert product ratios in Penning ionisation reactions with argon
Published in Molecular Physics, 2019
Natan Bibelnik, Sasha Gersten, Alon B Henson, Etay Lavert-Ofir, Yuval Shagam, Wojciech Skomorowski, Christiane P Koch, Edvardas Narevicius
One of the central goals of the chemical sciences is to obtain a comprehensive characterisation and microscopic understanding of chemical processes. An important parameter in describing a chemical reaction with more than one possible outcome is the branching ratio. Very often, it is determined empirically and is assumed to vary slowly with changes in the collision energy. Nevertheless, the dependence of the branching ratio on the collision kinetic energy reveals interesting information about the reaction dynamics. In order to observe significant changes in the branching ratio, it is essential to perform measurements over a wide range of collision energies. In our experiments, we measure the branching ratio over collision energies ranging from room temperature, where classical models can explain the dynamics, down to the cold collision regime, where the reaction dynamics is largely governed by quantum effects.