857 In this Chapter we begin our discussion of nuclear physics. We study the properties of nuclei, the various forms of radioactivity, and how radioactive decay can be used in a variety of fields to determine the age of old objects, from bones and trees to rocks and other mineral substances, and obtain information on the history of the Earth. Shown is one version of a Chart of the Nuclides . Each horizontal row has a square for each known isotope (nuclide) of one element with a particular Z value ( number of electrons in the neutral atom number of protons in the nucleus). At the far left is a white box with the average atomic weight (or a range if uncertain) of the naturally occurring isotopes of that element. Each vertical column contains nuclides with the same neutron number N . For (to right of pencil), starting at the bottom, there is a lone neutron, then above it , then and . Each square is color coded: black means a stable nuclide. Radioactive nuclides are blue green for decay, pink for decay or electron capture ( ) such as , yellow for decay, and so on. Thus and are stable but (tritium) undergoes decay with half-life 12.3 years (“a” is for Latin “anno” year). The squares contain the atomic mass of that isotope, or half-life and energy released if radioactive. Other details may be alternate decay modes and certain cross sections ( ). s = = b – 3 1 H 2 1 H 1 1 H a 7 4 Be e b ± b – 4 3 Li 3 2 He 2 1 H N = 1 = = C H A P T E R Nuclear Physics and Radioactivity CHAPTER-OPENING QUESTION —Guess now! If half of an sample of decays in 5.3 years, how much is left in 10.6 years? (a) (b) (c) (d) (e) I n the early part of the twentieth century, Rutherford’s experiments (Section 27 – 10) led to the idea that at the center of an atom there is a tiny but massive nucleus with a positive charge. At the same time that the quantum theory was being developed and scientists were attempting to understand the structure of the atom and its electrons, investigations into the nucleus itself had also begun. In this Chapter and the next, we take a brief look at nuclear physics . 0 m g. 40 m g. 30 m g. 20 m g. 10 m g. 27 60 Co 27 60 Co 80- m g CONTENTS 30–1 Structure and Properties of the Nucleus 30–2 Binding Energy and Nuclear Forces 30–3 Radioactivity 30–4 Alpha Decay 30–5 Beta Decay 30–6 Gamma Decay 30–7 Conservation of Nucleon Number and Other Conservation Laws 30–8 Half-Life and Rate of Decay 30–9 Calculations Involving Decay Rates and Half-Life 30–10 Decay Series 30–11 Radioactive Dating *30–12 Stability and Tunneling 30–13 Detection of Particles 30
30–1 Structure and Properties of the Nucleus An important question for physicists was whether the nucleus had a structure, and what that structure might be. By the early 1930s, a model of the nucleus had been developed that is still useful. According to this model, a nucleus is made up of two types of particles: protons and neutrons. [These “particles” also have wave properties, but for ease of visualization and language, we usually refer to them simply as “particles.”] A proton is the nucleus of the simplest atom, hydrogen.
- Spring '14