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Electrical Characterization of Defects Introduced in Epitaxially Grown GaAs by Electron-, Proton- and He-Ion Irradiation
Published in Kazumi Wada, Stella W. Pang, Defects in Optoelectronic Materials, 2021
Next, consider the defects introduced in the same GaAs by 200 MeV proton irradiation at a dose of 1013 H+ cm−2 in a cyclotron (National Accelerator Center, Faure, South Africa) [105]. The DLTS spectrum (curve (a) in Figure 12) shows that the most significant difference between 200 MeV and 40 keV-1 MeV proton irradiation is that the 200 MeV spectrum contains a broad asymmetric peak, Ep7, just below 300 K. In contrast to 40 keV-1 MeV proton irradiation, the Ep7 peak height is larger than that of Ep3 and Ep4, and is about the same as the Ep1 and Ep2 peak heights. The activation energy, ET, and capture cross section, σa, of Ep7 were determined as 0.68 eV and 4 × 10−12 cm2, respectively. This is very similar to that of the En5 [106] and the “U-band” [107], observed in neutron-irradiated n-GaAs. The similarity between Ep7 and the neutron introduced defects, En5 and the “U-band”, suggests that Ep7 may be created by neutrons or other nuclear fragments produced in GaAs when high energy protons penetrate, or pass through, the Ga and As nuclei. As has been shown in Section 2, the threshold energy for a proton to enter Ga and As nuclei is about 6 MeV. This means that 200 MeV protons can easily penetrate Ga and As nuclei and thus cause nuclear reactions, including neutron emission by, for example, (p, n) reactions. The neutrons thus created can, in turn, introduce Ep7.
Detectors
Published in C. R. Kitchin, Astrophysical Techniques, 2020
The first neutrino telescope to be built was designed to detect electron neutrinos through the chlorine-to-argon reaction given in Equation 1.96. The threshold energy of the neutrino for this reaction is 0.814 MeV, so that 80% of the neutrinos from the Sun that are detectable by this experiment arise from the decay of boron to beryllium (Figure 1.104) in a low probability side chain of the proton-proton (pp) reaction () B58→B48e+e++νe
X-Ray Interactions and Energy Deposition
Published in Jerry J. Battista, Introduction to Megavoltage X-Ray Dose Computation Algorithms, 2019
Jerry J. Battista, George Hajdok
Pair production causes the incoming photon to be fully absorbed in the vicinity of the nucleus. For this event, the minimum or threshold energy for the incoming photon is 1.022 MeV – the combined rest mass energy of the electron-positron created out of this process. Pair production can also occur with orbital electrons instead of the nucleus with a greater threshold of 2.04 MeV, yielding a triplet of emerging particles (2 electrons, 1 positron). While triplet events can involve any one of the Z orbital electrons, these events are less prevalent than nuclear events because of the higher energy threshold and screening of the Coulomb field. In either pair or triplet production, the energy exceeding threshold energy is shared as kinetic energy among the emerging charged particles. The probability of nuclear pair production events per atom is quadratically dependent on atomic number (Z2). The emerging positron has a very high likelihood of annihilation in a sea of numerous host electrons particularly as the positron slows down. Upon annihilation, a pair of gamma rays will be emitted. If the positron exhausts all of its kinetic energy and recombines with a quasi-stationary electron, the gamma emissions will each inherit characteristic energies of 0.511 MeV and launch in directly opposite directions; otherwise the gamma rays will split a share of the residual kinetic energy and emerge at oblique angles.
Influence of Particle Beam and Accelerator Type on ADS Efficiency
Published in Nuclear Science and Engineering, 2023
M. Paraipan, V. M. Javadova, S. I. Tyutyunnikov
The dependence of energy gain on particle energy and mass is given in Fig. 8a. The same dependence for net power is shown in Fig. 8b. When accelerated in a linac, the optimal energy of the proton beam is 1.5 GeV with a G value of 14. The values of G and Pnet corresponding to the 1.5-GeV proton are shown in the figures with dashed lines. The energy gain of the deuteron is higher than of the proton for energies up to 1 GeV/n and approaches the proton value at 2 GeV/n. The ions 4He, 7Li, and 9Be have values of G higher than the 1.5-GeV proton in the entire energy range. In this case, G rises until ion energy of ~0.5 GeV/n, when a plateau is reached at values of 25 to 35. In the case of ions with higher mass, G exceeds the proton value after some threshold energy (0.25 GeV/n for C and 0.3 GeV/n for O and Ne), and the plateau is reached at higher energies. However, when one compares the energy efficiency of different beams beside the values of G, the values of Pnet must also be taken into account. All ions need some threshold energy to equalize the Pnet value of the 1.5-GeV proton. The most interesting results are obtained with 7Li and 9Be beams that need to be accelerated at 0.25 to 0.3 GeV/n to become equivalent with the 1.5-GeV proton from the point of view of Pnet. That allows using an accelerator 2 to 2.5 times shorter, which lowers construction and maintenance costs.
Silicon Solar Cells for Post-Detonation Monitoring and Gamma-Radiation Effects
Published in Nuclear Science and Engineering, 2022
Praneeth Kandlakunta, Matthew Van Zile, Lei Raymond Cao
where is the electron mass and is the speed of light. Equation (1) indicates that an of 21 eV can be transferred to a Si atom if the incident electron has a kinetic energy of at least 222 keV. Thus, DD due to the irradiation of Si by electrons of energy <222 keV is improbable, however, TID effects may still occur in devices such as Si MOS transistors. The threshold energy of different radiation particles to produce an atom displacement in Si is listed in Table I. As one might expect through kinematic arguments, the threshold energy decreases with an increase in the mass of the incoming particle.
Velocity map imaging studies of the photodissociation of CS2 by two-photon excitation at around 303–315 nm
Published in Molecular Physics, 2021
Zhenxing Li, Min Zhao, Ting Xie, Yao Chang, Zijie Luo, Zhichao Chen, Xingan Wang, Kaijun Yuan, Xueming Yang
Figures 3 and 4 show the relative vibrational state populations of CS products. The CS (X1Σg+) products are highly vibrationally excited, with the largest population at v=11, 12, 13, and 14 for the S (1D2) channel with the photolysis wavelength 314.545 nm, 312.983 nm, 307.322 nm, and 303.878 nm, respectively. The CS (X1Σg+) products for the S (3P0) channel show quite similar distributions at all four wavelengths. The vibrational state population maximises at v=18–21 and extends to around v=24–26, due to more available energy in the S (3P0) channel. Furthermore, a narrow peak at very low kinetic energy region at 307.322 nm is assigned to the CS (a3Φ) products with v=0, suggesting the excitation energy is just well above the threshold energy of the channel (4). At 303.878 nm, the population of the CS (a3Φ) products is significantly increased, which is in accord with that observed in the shorter wavelengths in the VUV region [18].