Chapter 24: Nuclear Fission and Nuclear Fusion

Table of Contents

24.1 Introduction

In this chapter, we will explore two essential nuclear reactions: nuclear fission and nuclear fusion. These reactions involve the release of significant amounts of energy due to the conversion of mass into energy, as described by Einstein’s famous equation, $E=mc^2$ . We will discuss the principles behind these reactions and their various applications.

24.2 Nuclear Fission

Nuclear fission is a process in which a heavy atomic nucleus splits into two lighter nuclei, accompanied by the release of energy and, often, the emission of neutrons.

24.2.1 Chain Reactions

A fission event can release multiple neutrons, which can then cause other fission reactions in a process known as a chain reaction. In a controlled chain reaction, as used in nuclear power plants, the rate of fission is maintained at a steady pace. In an uncontrolled chain reaction, such as in a nuclear bomb, the rate of fission rapidly increases, leading to a massive release of energy.

24.2.2 Nuclear Power Plants

Nuclear power plants harness the energy released during controlled nuclear fission to generate electricity. The heat produced during fission is used to heat water and produce steam, which drives turbines connected to electrical generators. Common fissionable materials used in nuclear power plants include uranium-235 and plutonium-239.

24.3 Nuclear Fusion

Nuclear fusion is the process by which two light atomic nuclei combine to form a single, more massive nucleus, releasing energy in the process.

24.3.1 Fusion in Stars

The primary source of energy in stars, including the Sun, is nuclear fusion. The most common fusion process in stars is the proton-proton chain, which involves the fusion of hydrogen nuclei (protons) to form helium. This process releases energy in the form of gamma-ray photons, neutrinos, and kinetic energy of the reaction products.

24.3.2 Controlled Fusion

Controlled nuclear fusion has been pursued as a potential source of clean and sustainable energy on Earth. The most widely studied fusion reaction for power generation is the fusion of two hydrogen isotopes, deuterium and tritium, to form helium and a neutron. However, achieving controlled fusion has proven to be extremely challenging due to the high temperatures and pressures required to overcome the electrostatic repulsion between the positively charged nuclei.

24.3.3 Fusion Devices

Various devices have been developed in attempts to achieve controlled fusion, including magnetic confinement devices, such as tokamaks and stellarators, and inertial confinement devices, like laser-driven implosion systems. While progress has been made, net energy production from controlled fusion has not yet been achieved.

24.4 Binding Energy and Nuclear Stability

The stability of a nucleus depends on the balance between the attractive strong nuclear force and the repulsive electrostatic force between protons. The binding energy per nucleon, $E_\text{bind}$ , is an indicator of the nuclear stability. It is the energy required to disassemble a nucleus into its constituent protons and neutrons. The binding energy per nucleon can be calculated using the following equation:

$E_\text{bind} = \dfrac{Zm_pc^2 + Nm_nc^2 - M_\text{atom}c^2}{A}$

where $Z$ is the number of protons, $N$ is the number of neutrons, $m_p$ and $m_n$ are the masses of a proton and neutron, respectively, $M_\text{atom}$ is the mass of the atom, and $A = Z + N$ is the total number of nucleons.

Chapter Summary

In this chapter, we discussed nuclear fission and nuclear fusion, two fundamental nuclear reactions that involve the release of significant amounts of energy. Nuclear fission, the process by which a heavy nucleus splits into lighter nuclei, is utilized in nuclear power plants and atomic weapons. Nuclear fusion, the process of combining two light nuclei into a heavier one, is the primary energy source in stars and has been pursued as a potential source of clean and sustainable energy on Earth. Both nuclear fission and fusion demonstrate the immense power stored within atomic nuclei and the potential applications of harnessing such energy for human use.

Continue to Chapter 25: Introduction to Particle Physics

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Chapter 24: Nuclear Fission and Nuclear Fusion

24.1 Introduction