同一原子番号を持つものの中性子数が異なる核種の関係を同位体と呼びます。同位体の多くは安定同位体、それ以外はその核種の不安定性から放射能を放出して放射性崩壊を起こす能力を持ちます。核兵器や原子力、医療、放射性炭素年代測定、地球の年齢や太陽系の起源の確立に用いられるのが後者で、これがなぜ幅広い科学領域、考古学研究で重要なのか、同位体の性質を概観し、多岐にわたる応用を考察します。
　　

• Explains the role of isotopes in tackling challenges such as climate change, cancer treatment, Earth's age and origin, and nuclear accidents
• Considers the use of isotopes in archaeology for carbon dating
• Describes the various technologies used to measure the proportions of radioactive and stable isotopes

An isotope is a variant form of a chemical element, containing a different number of neutrons in its nucleus. Most elements exist as several isotopes. Many are stable while others are radioactive, and some may only exist fleetingly before decaying into other elements.

In this Very Short Introduction, Rob Ellam explains how isotopes have proved enormously important across all the sciences and in archaeology. Radioactive isotopes may be familiar from their use in nuclear weapons, nuclear power, and in medicine, as well as in carbon dating. They have been central to establishing the age of the Earth and the origins of the solar system. Combining previous and new research, Ellam provides an overview of the nature of stable and radioactive isotopes, and considers their wide range of modern applications.