Chapter 9: Nuclear Chemistry
Introduction
Nuclear chemistry focuses on the reactions and properties of atomic nuclei, uncovering the immense energy stored within atoms. Unlike traditional chemistry, which involves electron interactions, nuclear chemistry examines processes like radioactive decay, nuclear fission, and nuclear fusion, where changes in the nucleus result in the transformation of elements and the release or absorption of energy. These processes release immense energy but also pose unique challenges. For example, on April 26, 1986, a catastrophic nuclear disaster occured at the Chernobyl Nuclear Power Plant in Ukraine (then part of the Soviet Union).
During a late-night safety test, reactor 4 experienced a sudden and uncontrollable power surge due to design flaws and operator errors. This caused the reactor core to overheat, leading to a series of explosions that destroyed the reactor and released massive amounts of radioactive material into the environment.
The explosion exposed the reactor to the open air, igniting fires and sending radioactive particles high into the atmosphere, where they spread across Europe. The disaster directly caused the deaths of two plant workers that night and dozens more from acute radiation sickness in the following weeks. Long-term health effects, including cancer and birth defects, have impacted thousands. The event remains one of the worst nuclear accidents in history, leading to significant changes in global nuclear safety protocols and practices. The site is now enclosed by a massive containment structure, but the area around it, known as the Chernobyl Exclusion Zone , remains uninhabitable due to lingering radiation.
Figure 9.1: Latent radioactivity at the Chernobyl reactor site 25 years later. (CC-BY-SA 2.0 2010; Roman Harak via WikiMedia Commons ).
However, applications of nuclear chemistry are vast and impactful, ranging from medical imaging and cancer therapy to energy generation in addition to nuclear reactors. Natural phenomena, such as the heat produced in Earth's core and the synthesis of elements in stars, are also governed by atomic nuclei. By studying nuclear chemistry, we gain insights into both the destructive and constructive potential of the atom's most fundamental components.
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- 9.2: Radioactive Decay
- Nuclei can undergo reactions that change their number of protons, number of neutrons, or energy state. Many different particles can be involved and the most common are protons, neutrons, positrons, alpha (α) particles, beta (β) particles (high-energy electrons), and gamma (γ) rays (which compose high-energy electromagnetic radiation). As with chemical reactions, nuclear reactions are always balanced. When a nuclear reaction occurs, the total mass (number) and the total charge remain unchanged.
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- 9.3: Nuclear Stability
- Many elements have at least one isotope whose atomic nucleus is stable indefinitely, but all elements have isotopes that are unstable and decay, at measurable rates by emitting radiation. Some elements have no stable isotopes and eventually decay to other elements. In contrast to the chemical reactions that were the main focus of earlier chapters and are due to changes in the arrangements of the valence electrons of atoms, the nuclear decay results in changes within atomic nuclei.
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- 9.4: Nuclear Transmutation
- It is possible to produce new atoms by bombarding other atoms with nuclei or high-speed particles. The products of these transmutation reactions can be stable or radioactive. A number of artificial elements, including technetium, astatine, and the transuranium elements, have been produced in this way.
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- 9.5: Fission and Nuclear Power
- Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger binding energies per nucleon. Sometimes neutrons are also produced. This decomposition is called fission, the breaking of a large nucleus into smaller pieces. The breaking is rather random with the formation of a large number of different products. Fission usually does not occur naturally, but is induced by bombardment with neutrons.
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- 9.6: Fusion - How the Elements Formed
- Unlike a chemical reaction, a nuclear reaction results in a significant change in mass and an associated change of energy, as described by Einstein’s equation. Nuclear reactions are accompanied by large changes in energy, which result in detectable changes in mass. The experimentally determined mass of an atom is always less than the sum of the masses of the component particles (protons, neutrons, and electrons) by an amount called the mass defect that corresponds to the nuclear binding energy.
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- 9.7: Applications of Radioactivity
- Compounds known as radioactive tracers can be used to follow reactions, track the distribution of a substance, diagnose and treat medical conditions, and much more. Other radioactive substances are helpful for controlling pests, visualizing structures, providing fire warnings, and for many other applications. Hundreds of millions of nuclear medicine tests and procedures, using a wide variety of radioisotopes with relatively short half-lives, are performed every year in the US.