![]() Radon gas is also produced ( 222Rn in the series), an increasingly recognized naturally occurring hazard. The decay series that starts from 238U is of particular interest, since it produces the radioactive isotopes 226Ra and 210Po, which the Curies first discovered (see Figure 1). Others, such as 238U, decay to another unstable nuclide, resulting in a decay series in which each subsequent nuclide decays until a stable nuclide is finally produced. For example, 60Co is unstable and decays directly to 60Ni, which is stable. Some radioactive nuclides decay in a single step to a stable nucleus. We call the original nuclide the parent and its decay products the daughters. Unstable nuclides decay (that is, they are radioactive), eventually producing a stable nuclide after many decays. Some nuclides are stable, apparently living forever. In this section, we explore the major modes of nuclear decay and, like those who first explored them, we will discover evidence of previously unknown particles and conservation laws. Nuclear decay gave the first indication of the connection between mass and energy, and it revealed the existence of two of the four basic forces in nature. Nuclear decay has provided an amazing window into the realm of the very small. Calculate the energy emitted during nuclear decay.For example, rubidium-83 (37 protons, 46 neutrons) will decay to krypton-83 (36 protons, 47 neutrons) solely by electron capture (the energy difference, or decay energy, is about 0.9 MeV).By the end of this section, you will be able to: If the energy difference between the parent atom and the daughter atom is less than 1.022 MeV, positron emission is forbidden as not enough decay energy is available to allow it, and thus electron capture is the sole decay mode. Electron capture is sometimes called inverse beta decay, though this term usually refers to the interaction of an electron antineutrino with a proton. In nuclear physics, beta decay is a type of radioactive decay in which a beta ray (fast energetic electron or positron) and a neutrino are emitted from an atomic nucleus. Electron capture is sometimes included as a type of beta decay, because the basic nuclear process, mediated by the weak force, is the same. Electron capture is always an alternative decay mode for radioactive isotopes that do have sufficient energy to decay by positron emission. However, a positive atomic ion may result from further Auger electron emission.Įlectron capture is an example of weak interaction, one of the four fundamental forces.Įlectron capture is the primary decay mode for isotopes with a relative superabundance of protons in the nucleus, but with insufficient energy difference between the isotope and its prospective daughter (the isobar with one less positive charge) for the nuclide to decay by emitting a positron. Simple electron capture by itself results in a neutral atom, since the loss of the electron in the electron shell is balanced by a loss of positive nuclear charge. Electron capture sometimes also results in the Auger effect, where an electron is ejected from the atom's electron shell due to interactions between the atom's electrons in the process of seeking a lower energy electron state.įollowing electron capture, the atomic number is reduced by one, the neutron number is increased by one, and there is no change in mass number. Usually, a gamma ray is emitted during this transition, but nuclear de-excitation may also take place by internal conversion.įollowing capture of an inner electron from the atom, an outer electron replaces the electron that was captured and one or more characteristic X-ray photons is emitted in this process. The resulting daughter nuclide, if it is in an excited state, then transitions to its ground state. Similarly, the momentum of the neutrino emission causes the daughter atom to recoil with a single characteristic momentum. Since this single emitted neutrino carries the entire decay energy, it has this single characteristic energy. The outer electron is ejected from the atom, leaving a positive ion. ![]() Lower right: In the Auger effect, the energy absorbed when the outer electron replaces the inner electron is transferred to an outer electron. An x-ray, equal in energy to the difference between the two electron shells, is emitted. Lower left: An outer electron replaces the "missing" electron. Process in which a proton-rich nuclide absorbs an inner atomic electron
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