Chapter 43 Nuclear Physics PowerPoint Lectures for University Physics, Thirteenth Edition Hugh D. Young and Roger A. Freedman Lectures by Wayne Anderson
Goals for Chapter 43 To understand some key properties of nuclei To see how nuclear binding energy depends on the number of protons and neutrons To investigate radioactive decay To learn about hazards and medical uses of radiation To analyze nuclear reactions To investigate nuclear fission To understand the nuclear reactions in our sun
Introduction How can we date ancient biological artifacts? Most of the mass of an atom is found in its tiny nucleus. Some nuclei are stable, but others spontaneously decay. Fission and fusion are important nuclear reactions. We would not exist without the fusion in our sun.
Properties of nuclei The nucleon number A is the total number of protons and neutrons in the nucleus. The radius of most nuclei is given by R = R 0 A 1/3. All nuclei have approximately the same density. Follow Example 43.1.
Q43.1 A nucleus of neon-20 has 10 protons and 10 neutrons. A nucleus of terbium-160 has 65 protons and 95 neutrons. Compared to the radius of a neon-20 nucleus, the radius of a terbium-160 nucleus is A. 9.5 times larger. B. 8 times larger. C. 6.5 times larger. D. 4 times larger. E. 2 times larger.
A43.1 A nucleus of neon-20 has 10 protons and 10 neutrons. A nucleus of terbium-160 has 65 protons and 95 neutrons. Compared to the radius of a neon-20 nucleus, the radius of a terbium-160 nucleus is A. 9.5 times larger. B. 8 times larger. C. 6.5 times larger. D. 4 times larger. E. 2 times larger.
Nuclides and isotopes The atomic number Z is the number of protons in the nucleus. The neutron number N is the number of neutrons in the nucleus. Therefore A = Z + N. A nuclide is a single nuclear species having specific values for both Z and N. The isotopes of an element have different numbers of neutrons. Follow the text discussion of nuclear spin and magnetic moments. Follow Example 43.2 on proton spin flips.
NMR and MRI Follow the text discussion of nuclear magnetic resonance and MRI, using Figure 43.1 below.
Nuclear binding energy The binding energy E B of a nucleus is the energy that must be added to separate the nucleons. Follow the text discussion of nuclear binding energy, using Figure 43.2 (right). Read Problem-Solving Strategy 43.1. Follow Example 43.3 on strongly bound nuclei.
The nuclear force The nuclear force binds protons and neutrons together. It is an example of the strong interaction. Important characteristics of the nuclear force: It does not depend on charge. Protons and neutrons are bound. It has a short range, of the order of nuclear dimensions. Because of its short range, a nucleon only interacts with those in its immediate vicinity. It favors binding of pairs of protons or neutrons with opposite spins and with pairs of pairs (a pair of protons and a pair of neutrons, each pair having opposite spins).
Q43.2 Why do stable nuclei with many nucleons (those with a large value of A) have more neutrons than protons? A. An individual nucleon interacts via the nuclear force with only a few of its neighboring nucleons. B. The electric force between protons acts over long distances. C. The nuclear force favors pairing of both neutrons and protons. D. both A. and B. E. all of A., B., and C.
A43.2 Why do stable nuclei with many nucleons (those with a large value of A) have more neutrons than protons? A. An individual nucleon interacts via the nuclear force with only a few of its neighboring nucleons. B. The electric force between protons acts over long distances. C. The nuclear force favors pairing of both neutrons and protons. D. both A. and B. E. all of A., B., and C.
Nuclear models Follow text discussion of the liquid-drop model and the shell model. Figure 43.3 (right) shows the approximate potential-energy functions for a nucleon in a nucleus. Follow Example 43.4.
Nuclear stability and radioactivity Radioactivity is the decay of unstable nuclides by the emission of particles and electromagnetic radiation. Figure 43.4 (right) is a Segrè chart showing N versus Z for stable nuclides.
Alpha decay An alpha particle is a 4 He nucleus. Figure 43.5 shows the alpha decay of the 226 Ra nuclide. Follow Example 43.5.
Q43.3 Which kinds of unstable nuclei typically decay by emitting an alpha particle? A. those with too many neutrons B. those with too many protons C. those with too many neutrons and too many protons D. Misleading question the numbers of neutrons and protons in a nucleus are unrelated to whether or not it emits an alpha particle.
A43.3 Which kinds of unstable nuclei typically decay by emitting an alpha particle? A. those with too many neutrons B. those with too many protons C. those with too many neutrons and too many protons D. Misleading question the numbers of neutrons and protons in a nucleus are unrelated to whether or not it emits an alpha particle.
Beta and gamma decay There are three types of beta decay: beta-minus, beta-plus, and electron capture. A beta-minus particle is an electron. A gamma ray is a photon. Follow the text discussion of beta decay and gamma decay. Follow Example 43.6 on cobalt-60. Follow Example 43.7 on cobalt-57.
Q43.4 Which kinds of unstable nuclei typically decay by emitting an electron? A. those with too many neutrons B. those with too many protons C. those with too many neutrons and too many protons D. Misleading question the numbers of neutrons and protons in a nucleus are unrelated to whether or not it emits an electron.
A43.4 Which kinds of unstable nuclei typically decay by emitting an electron? A. those with too many neutrons B. those with too many protons C. those with too many neutrons and too many protons D. Misleading question the numbers of neutrons and protons in a nucleus are unrelated to whether or not it emits an electron.
Q43.5 Which kinds of unstable nuclei typically decay by emitting a gamma-ray photon? A. those with too many neutrons B. those with too many protons C. those with too many neutrons and too many protons D. Misleading question the numbers of neutrons and protons in a nucleus are unrelated to whether or not it emits gamma rays.
A43.5 Which kinds of unstable nuclei typically decay by emitting a gamma-ray photon? A. those with too many neutrons B. those with too many protons C. those with too many neutrons and too many protons D. Misleading question the numbers of neutrons and protons in a nucleus are unrelated to whether or not it emits gamma rays.
Natural radioactivity Figure 43.7 (right) shows a Segrè chart for the 238 U decay series.
Activities and half-lives The half-life is the time for the number of radioactive nuclei to decrease to one-half of their original number. The number of remaining nuclei decreases exponentially (see Figure 43.8 at right). Follow the text discussion of decay rates and radioactive dating. Follow Example 43.8 on 57 Co activity. Follow Example 43.9 on radiocarbon dating.
Q43.6 As a sample of radioactive material decays, the decay rate A. is directly proportional to the half-life and directly proportional to the number of radioactive nuclei remaining. B. is directly proportional to the half-life and inversely proportional to the number of radioactive nuclei remaining. C. is inversely proportional to the half-life and directly proportional to the number of radioactive nuclei remaining. D. is inversely proportional to the half-life and inversely proportional to the number of radioactive nuclei remaining.
A43.6 As a sample of radioactive material decays, the decay rate A. is directly proportional to the half-life and directly proportional to the number of radioactive nuclei remaining. B. is directly proportional to the half-life and inversely proportional to the number of radioactive nuclei remaining. C. is inversely proportional to the half-life and directly proportional to the number of radioactive nuclei remaining. D. is inversely proportional to the half-life and inversely proportional to the number of radioactive nuclei remaining.
Biological effects of radiation Follow the text discussion of the biological effects of radiation. Table 43.3 gives the RBE for several types of radiation. Figure 43.9 shows sources of U.S. radiation exposure. Follow Example 43.10 about a medical x ray.
Nuclear reactions A nuclear reaction is a rearrangement of nuclear components due to bombardment by a particle rather than a spontaneous natural process. The difference in masses before and after the reaction corresponds to the reaction energy Q. Follow Example 43.11, which looks at exoergic and endoergic reactions.
Nuclear fission Nuclear fission is a decay process in which an unstable nucleus splits into two fragments (the fission fragments) of comparable mass. Figure 43.11 (right) shows the mass distribution of the fission fragments from the fission of 236 U *.
Liquid-drop model The liquid-drop model helps explain fission. See Figure 43.12 below. Figure 43.13 (right) shows the potential energy function of two fission fragments.
Chain reactions The neutrons released by fission can cause a chain reaction (see Figure 43.14 below).
Nuclear reactors A nuclear reactor is a system in which a controlled nuclear chain reaction is used to liberate energy. Figure 43.15 below illustrates a nuclear power plant. Follow Example 43.12.
Nuclear fusion In a nuclear fusion reaction, two or more light nuclei fuse to form a larger nucleus. Figure 43.16 below illustrates the proton-proton chain, which is the main energy source in our sun. Follow Example 43.13.
Q43.7 Why does nuclear fusion of hydrogen require high temperatures? A. Positive charges repel each other. B. The nuclear force only acts at short range. C. both A. and B. D. neither A. nor B.
A43.7 Why does nuclear fusion of hydrogen require high temperatures? A. Positive charges repel each other. B. The nuclear force only acts at short range. C. both A. and B. D. neither A. nor B.