Nuclear Decay and Conservation Laws Quiz

PDF page 1500: more than one mode. You can see why radium and polonium are found in uranium ore. A stable isotope of lead is the end product of the series. Note that the daughters of decay shown in Figure 31.14 always have two fewer protons and two fewer neutrons than the parent. This seems reasonable, since we know that decay is the emission of a nucleus, which has two protons and two neutrons. The daughters of decay have one less neutron and one more proton than their parent. Beta decay is a little more subtle, as we shall see. No decays are shown in the figure, because they do not produce a daughter that differs from the parent.

PDF page 1501: FIGURE 31.15 Alpha decay is the separation of a

PDF page 1500: more than one mode. You can see why radium and polonium are found in uranium ore. A stable isotope of lead is the end product of the series. Note that the daughters of decay shown in Figure 31.14 always have two fewer protons and two fewer neutrons than the parent. This seems reasonable, since we know that decay is the emission of a nucleus, which has two protons and two neutrons. The daughters of decay have one less neutron and one more proton than their parent. Beta decay is a little more subtle, as we shall see. No decays are shown in the figure, because they do not produce a daughter that differs from the parent.

PDF page 1503: FIGURE 31.17 In decay, the parent nucleus emits an electron and an antineutrino. The daughter nucleus has one more proton and one

PDF page 1499: Nuclear decay has provided an amazing window into the realm of the very small. 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. 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. Some nuclides are stable, apparently living forever. Unstable nuclides decay (that is, they are radioactive), eventually producing a stable nuclide after many decays. We call the original nuclide the parent and its decay products the daughters. Some radioactive nuclides decay in a single step to a stable nucleus. For example, is unstable and decays directly to , which is stable. Others, such as , decay to another unstable nuclide, resulting in a decay series in which each subsequent nuclide decays until a stable nuclide is finally produced. The decay series that starts from is of particular interest, since it produces the radioactive isotopes and , which the Curies first discovered (see Figure 31.14). Radon gas is also produced ( in the series), an increasingly recognized naturally occurring hazard. Since radon is a noble gas, it emanates from materials, such as soil, containing even trace amounts of and can be inhaled. The decay of radon and its daughters produces internal damage. The decay series ends with , a stable isotope of lead.

PDF page 1501: nucleus from the parent. The daughter nucleus has two fewer protons and two fewer neutrons than the parent. Alpha decay occurs spontaneously only if the daughter and nucleus have less total mass than the parent. If you examine the periodic table of the elements, you will find that Th has , two fewer than U, which has . Similarly, in the second decay equation, we see that U has two fewer protons than Pu, which has . The general rule for decay is best written in the format . If a certain nuclide is known to decay (generally this information must be looked up in a table of isotopes, such as in Appendix B), its decay equation is

PDF page 1501: where Y is the nuclide that has two fewer protons than X, such as Th having two fewer than U. So if you were told that decays and were asked to write the complete decay equation, you would first look up which element has two fewer protons (an atomic number two lower) and find that this is uranium. Then since four nucleons have broken away from the original 239, its atomic mass would be 235. It is instructive to examine conservation laws related to decay. You can see from the equation that total charge is conserved. Linear and angular momentum are conserved, too. Although conserved angular momentum is not of great consequence in this type of decay, conservation of linear momentum has interesting consequences. If the nucleus is at rest when it decays, its momentum is zero. In that case, the fragments must fly in opposite directions with equal-magnitude momenta so that total momentum remains zero. This results in the particle carrying away most of the energy, as a bullet from a heavy rifle carries away most of the energy of the powder burned to shoot it. Total mass–energy is also conserved: the energy produced in the decay comes from conversion of a fraction of the original mass. As discussed in Atomic Physics, the general relationship is 31.16 Here, is the nuclear reaction energy (the reaction can be nuclear decay or any other reaction), and is the difference in mass between initial and final products. When the final products have less total mass, is positive, and the reaction releases energy (is exothermic). When the products have greater total mass, the reaction is endothermic ( is negative) and must be induced with an energy input. For decay to be spontaneous, the decay products must have smaller mass than the parent.

PDF page 1501: where Y is the nuclide that has two fewer protons than X, such as Th having two fewer than U. So if you were told that decays and were asked to write the complete decay equation, you would first look up which element has two fewer protons (an atomic number two lower) and find that this is uranium. Then since four nucleons have broken away from the original 239, its atomic mass would be 235. It is instructive to examine conservation laws related to decay. You can see from the equation that total charge is conserved. Linear and angular momentum are conserved, too. Although conserved angular momentum is not of great consequence in this type of decay, conservation of linear momentum has interesting consequences. If the nucleus is at rest when it decays, its momentum is zero. In that case, the fragments must fly in opposite directions with equal-magnitude momenta so that total momentum remains zero. This results in the particle carrying away most of the energy, as a bullet from a heavy rifle carries away most of the energy of the powder burned to shoot it. Total mass–energy is also conserved: the energy produced in the decay comes from conversion of a fraction of the original mass. As discussed in Atomic Physics, the general relationship is 31.16 Here, is the nuclear reaction energy (the reaction can be nuclear decay or any other reaction), and is the difference in mass between initial and final products. When the final products have less total mass, is positive, and the reaction releases energy (is exothermic). When the products have greater total mass, the reaction is endothermic ( is negative) and must be induced with an energy input. For decay to be spontaneous, the decay products must have smaller mass than the parent.

PDF page 1501: where Y is the nuclide that has two fewer protons than X, such as Th having two fewer than U. So if you were told that decays and were asked to write the complete decay equation, you would first look up which element has two fewer protons (an atomic number two lower) and find that this is uranium. Then since four nucleons have broken away from the original 239, its atomic mass would be 235. It is instructive to examine conservation laws related to decay. You can see from the equation that total charge is conserved. Linear and angular momentum are conserved, too. Although conserved angular momentum is not of great consequence in this type of decay, conservation of linear momentum has interesting consequences. If the nucleus is at rest when it decays, its momentum is zero. In that case, the fragments must fly in opposite directions with equal-magnitude momenta so that total momentum remains zero. This results in the particle carrying away most of the energy, as a bullet from a heavy rifle carries away most of the energy of the powder burned to shoot it. Total mass–energy is also conserved: the energy produced in the decay comes from conversion of a fraction of the original mass. As discussed in Atomic Physics, the general relationship is 31.16 Here, is the nuclear reaction energy (the reaction can be nuclear decay or any other reaction), and is the difference in mass between initial and final products. When the final products have less total mass, is positive, and the reaction releases energy (is exothermic). When the products have greater total mass, the reaction is endothermic ( is negative) and must be induced with an energy input. For decay to be spontaneous, the decay products must have smaller mass than the parent.

PDF page 1502: The energy released in this decay is in the range, about times as great as typical chemical reaction energies, consistent with many previous discussions. Most of this energy becomes kinetic energy of the particle (or nucleus), which moves away at high speed. The energy carried away by the recoil of the nucleus is much smaller in order to conserve momentum. The nucleus can be left in an excited state to later emit photons ( rays). This decay is spontaneous and releases energy, because the products have less mass than the parent nucleus. The question of why the products have less mass will be discussed in Binding Energy. Note that the masses given in Appendix A are atomic masses of neutral atoms, including their electrons. The mass of the electrons is the same before and after decay, and so their masses subtract out when finding . In this case, there are 94 electrons before and after the decay.

PDF page 1502: There are actually three types of beta decay. The first discovered was “ordinary” beta decay and is called decay or electron emission. The symbol represents an electron emitted in nuclear beta decay. Cobalt-60 is a nuclide that decays in the following manner: 31.21 The neutrino is a particle emitted in beta decay that was unanticipated and is of fundamental importance. The neutrino was not even proposed in theory until more than 20 years after beta decay was known to involve electron emissions. Neutrinos are so difficult to detect that the first direct evidence of them was not obtained until 1953. Neutrinos are nearly massless, have no charge, and do not interact with nucleons via the strong nuclear force. Traveling approximately at the speed of light, they have little time to affect any nucleus they encounter. This is, owing to the fact that they have no charge (and they are not EM waves), they do not interact through the EM force. They do interact via the relatively weak and very short range weak nuclear force. Consequently, neutrinos escape almost any detector and penetrate almost any shielding. However, neutrinos do carry energy, angular momentum (they are fermions with half-integral spin), and linear momentum away from a beta decay. When accurate measurements of beta decay were made, it became apparent that energy, angular momentum, and linear momentum were not accounted for by the daughter nucleus and electron alone. Either a previously unsuspected particle was carrying them away, or three conservation laws were being violated. Wolfgang Pauli made a formal proposal for the existence of neutrinos in 1930. The Italian-born American physicist Enrico Fermi (1901–1954) gave neutrinos their name, meaning little neutral ones, when he developed a sophisticated theory of beta decay (see

PDF page 1502: There are actually three types of beta decay. The first discovered was “ordinary” beta decay and is called decay or electron emission. The symbol represents an electron emitted in nuclear beta decay. Cobalt-60 is a nuclide that decays in the following manner: 31.21 The neutrino is a particle emitted in beta decay that was unanticipated and is of fundamental importance. The neutrino was not even proposed in theory until more than 20 years after beta decay was known to involve electron emissions. Neutrinos are so difficult to detect that the first direct evidence of them was not obtained until 1953. Neutrinos are nearly massless, have no charge, and do not interact with nucleons via the strong nuclear force. Traveling approximately at the speed of light, they have little time to affect any nucleus they encounter. This is, owing to the fact that they have no charge (and they are not EM waves), they do not interact through the EM force. They do interact via the relatively weak and very short range weak nuclear force. Consequently, neutrinos escape almost any detector and penetrate almost any shielding. However, neutrinos do carry energy, angular momentum (they are fermions with half-integral spin), and linear momentum away from a beta decay. When accurate measurements of beta decay were made, it became apparent that energy, angular momentum, and linear momentum were not accounted for by the daughter nucleus and electron alone. Either a previously unsuspected particle was carrying them away, or three conservation laws were being violated. Wolfgang Pauli made a formal proposal for the existence of neutrinos in 1930. The Italian-born American physicist Enrico Fermi (1901–1954) gave neutrinos their name, meaning little neutral ones, when he developed a sophisticated theory of beta decay (see

PDF page 1502: There are actually three types of beta decay. The first discovered was “ordinary” beta decay and is called decay or electron emission. The symbol represents an electron emitted in nuclear beta decay. Cobalt-60 is a nuclide that decays in the following manner: 31.21 The neutrino is a particle emitted in beta decay that was unanticipated and is of fundamental importance. The neutrino was not even proposed in theory until more than 20 years after beta decay was known to involve electron emissions. Neutrinos are so difficult to detect that the first direct evidence of them was not obtained until 1953. Neutrinos are nearly massless, have no charge, and do not interact with nucleons via the strong nuclear force. Traveling approximately at the speed of light, they have little time to affect any nucleus they encounter. This is, owing to the fact that they have no charge (and they are not EM waves), they do not interact through the EM force. They do interact via the relatively weak and very short range weak nuclear force. Consequently, neutrinos escape almost any detector and penetrate almost any shielding. However, neutrinos do carry energy, angular momentum (they are fermions with half-integral spin), and linear momentum away from a beta decay. When accurate measurements of beta decay were made, it became apparent that energy, angular momentum, and linear momentum were not accounted for by the daughter nucleus and electron alone. Either a previously unsuspected particle was carrying them away, or three conservation laws were being violated. Wolfgang Pauli made a formal proposal for the existence of neutrinos in 1930. The Italian-born American physicist Enrico Fermi (1901–1954) gave neutrinos their name, meaning little neutral ones, when he developed a sophisticated theory of beta decay (see

PDF page 1502: There are actually three types of beta decay. The first discovered was “ordinary” beta decay and is called decay or electron emission. The symbol represents an electron emitted in nuclear beta decay. Cobalt-60 is a nuclide that decays in the following manner: 31.21 The neutrino is a particle emitted in beta decay that was unanticipated and is of fundamental importance. The neutrino was not even proposed in theory until more than 20 years after beta decay was known to involve electron emissions. Neutrinos are so difficult to detect that the first direct evidence of them was not obtained until 1953. Neutrinos are nearly massless, have no charge, and do not interact with nucleons via the strong nuclear force. Traveling approximately at the speed of light, they have little time to affect any nucleus they encounter. This is, owing to the fact that they have no charge (and they are not EM waves), they do not interact through the EM force. They do interact via the relatively weak and very short range weak nuclear force. Consequently, neutrinos escape almost any detector and penetrate almost any shielding. However, neutrinos do carry energy, angular momentum (they are fermions with half-integral spin), and linear momentum away from a beta decay. When accurate measurements of beta decay were made, it became apparent that energy, angular momentum, and linear momentum were not accounted for by the daughter nucleus and electron alone. Either a previously unsuspected particle was carrying them away, or three conservation laws were being violated. Wolfgang Pauli made a formal proposal for the existence of neutrinos in 1930. The Italian-born American physicist Enrico Fermi (1901–1954) gave neutrinos their name, meaning little neutral ones, when he developed a sophisticated theory of beta decay (see

PDF page 1502: Figure 31.16). Part of Fermi’s theory was the identification of the weak nuclear force as being distinct from the

PDF page 1503: theoretical physics included the identification of the weak nuclear force. The fermi (fm) is named after him, as are an entire class of subatomic particles (fermions), an element (Fermium), and a major research laboratory (Fermilab). (credit: United States Department of Energy, Office of Public Affairs). (b) Chien-Shiung Wu undertook the experimentation to verify Fermi’s theory of beta decay. She became the world’s expert on the subject, and contributed to work that led to a Nobel Prize, even though she was denied the award. (credit: Smithsonian Institute) The neutrino also reveals a new conservation law. There are various families of particles, one of which is the electron family. We propose that the number of members of the electron family is constant in any process or any closed system. In our example of beta decay, there are no members of the electron family present before the decay, but after, there is an electron and a neutrino. So electrons are given an electron family number of . The neutrino in decay is an electron’s antineutrino, given the symbol , where is the Greek letter nu, and the subscript e means this neutrino is related to the electron. The bar indicates this is a particle of antimatter. (All particles have antimatter counterparts that are nearly identical except that they have the opposite charge. Antimatter is almost entirely absent on Earth, but it is found in nuclear decay and other nuclear and particle reactions as well as in outer