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Nucleus and Radioactivity
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
In alpha decay, a nucleus emits an α particle, the same as in the Rutherford experiment mentioned in Chapter 1, and which is nothing but a 4He nucleus, i.e., composed of two protons and two neutrons: XZA→YZ−2A−4+He24.
Nuclear Fuels, Nuclear Structure, the Mass Defect, and Radioactive Decay
Published in Robert E. Masterson, Introduction to Nuclear Reactor Physics, 2017
Extremely heavy atoms having an atomic weight greater than 110 can also become unstable and emit ionized helium nuclei to return to a stable state. These ionized helium nuclei are sometimes called alpha particles, and the corresponding radiation is then called alpha radiation. Polonium is an example of a heavy element that emits alpha particles. Another element that emits alpha particles is Americium, which is used in household smoke detectors. Alpha decay therefore requires two protons and two neutrons to be emitted from an unstable nucleus. Normally, alpha decay allows the resulting nucleus to become a more energetically stable structure.As mentioned previously, alpha decay is normally restricted to heavy elements having atomic weights greater than about 110. Alpha decay does NOT occur in lighter elements such as Iron, Carbon, Oxygen, or Zirconium because these nuclei are too light and their average binding energy per nucleon is too high. The resulting alpha particles do not travel as far as photons, beta rays, or γ-rays do. They have kinetic energies between 2 and 6 MeV, and they are normally deposited in the nuclear fuel rods close to the atoms that created them. Alpha decay is frequently a by-product of the process of neutron capture. In a Segre Chart (see Figure 6.19), alpha decay normally occurs in the top right-hand quadrant of the chart.
Radioactive Materials and Radioactive Decay
Published in Robert E. Masterson, Nuclear Engineering Fundamentals, 2017
Alpha decay is probably the most common form of natural radioactive decay for the heavy radioactive isotopes used in common nuclear fuels. When a heavy nucleus undergoes alpha decay, it emits an alpha particle, α, which is basically a helium 4 nucleus with the two electrons removed (see Figure 6.7). The emitted alpha particle is sometimes called a helium ion. The helium ion has a positive charge of +2, but because it is heavy and relatively slow moving compared to other particles that may be released, it usually travels no more than a couple of millimeters before it hits another atom, captures one or two free neutrons, and becomes an atom of helium gas. You may be surprised to learn that this mode of alpha decay is responsible for about 98% of the helium gas that is present in the earth’s atmosphere today. Among other things, alpha decay has produced so much atmospheric helium that it has been indirectly responsible for the production of various dirigibles and helium airships such as the Hindenburg and the Goodyear Blimp. Since an alpha particle consists of two protons and two neutrons, any atom that emits an alpha particle will have its atomic mass A reduced by 4 and its atomic number Z reduced by 2. Since the parent atom has two fewer protons, alpha decay always transforms a heavy element into a lighter element that has its atomic number reduced by 2. For example, when U-238 decays into Thorium-234 by alpha decay, the equation governing the reaction is
A Nuclear Decay Micropropulsion Technology Based on Spontaneous Alpha Decay
Published in Nuclear Science and Engineering, 2021
Shiyi He, Yan Xia, Fei Xu, Leidang Zhou, Xiaoping Ouyang
The nuclear process of alpha decay occurs when an excited nucleus spontaneously emits an alpha particle to reach a stable state.16 Alpha decay ejects high-energy alpha particles of 4 to 9 MeV spontaneously. A schematic diagram of the process is shown in Fig. 1. The nuclear reaction formula of alpha decay is shown as Eq. (1):