Zerfall

Zerfall is the German word for decay or disintegration. In physics, it designates the spontaneous transformation of an unstable atomic nucleus into a more stable configuration, typically accompanied by the emission of particles such as alpha or beta particles and electromagnetic radiation. The rate of Zerfall is probabilistic: each nucleus has a constant probability per unit time to decay, characterized by the decay constant lambda and the half-life t1/2, where t1/2 = ln(2)/lambda. The activity A of a sample is A = lambda N, where N is the number of undecayed nuclei.

There are several common modes of Zerfall. Alpha-Zerfall (α-Zerfall) involves emission of a helium-4 nucleus and reduces the atomic number by 2 and the mass number by 4. Beta-Zerfall (β-Zerfall) changes the atomic number by ±1 through emission of an electron or positron, with the mass number remaining unchanged. Gamma-Zerfall (γ-Zerfall) emits high-energy photons without changing the atomic composition, usually following alpha or beta decay as the nucleus settles to a lower energy state. Spontane Zerfall occurs without external influence; induced decay is studied in advanced particle physics and related fields.

Applications of Zerfall concepts include radiometric dating, nuclear medicine, and reactor physics. In dating, the decay of isotopes such as uranium-238 or carbon-14 provides age estimates. In medicine, short-lived isotopes are used for imaging or therapy. The term is common in German-language scientific literature and education, where Zerfall is often discussed alongside the Zerfallsgesetz (the decay law) and related concepts.