Radioactivity

Radioactivity is the spontaneous transformation or de-excitation of unstable atomic nuclei, accompanied by the emission of ionizing radiation. Its decay follows statistical laws, while individual nuclear events are unpredictable.

Alpha decay: A nuclear decay in which an atomic nucleus emits a helium-4 nucleus. It is one of the principal ways heavy radioactive nuclei shed mass and energy.
Atomic nucleus: The dense central region of an atom, composed of protons and neutrons. Radioactive transformations occur in this compact store of nuclear binding energy.
Radiometric dating: A method of determining age from measured radioactive decay and the abundance of parent and daughter isotopes. Known decay rates let radioactive isotopes date rocks, artifacts, and biological materials.
Ionizing radiation: Radiation energetic enough to remove electrons from atoms or molecules. Radioactive emissions belong to this broader class of radiation.
Henri Becquerel: The French physicist who discovered spontaneous uranium radiation in 1896. His experiments revealed emissions that did not require prior exposure to sunlight.
Beta decay: A nuclear transformation in which a neutron or proton changes type while an electron or positron is emitted. It changes a nucleus’s proton-to-neutron balance without ejecting a heavy fragment.
Isotope: One of two or more nuclides with the same proton number but different neutron numbers. Isotopes of an element can differ sharply in nuclear stability.
Radiocarbon dating: A dating method that estimates the age of once-living material from its carbon-14 content. It applies radioactive decay to archaeological and environmental samples.
Radiation dosimetry: The measurement and assessment of radiation dose absorbed by matter or living tissue. Dosimetry quantifies exposure from radioactive sources in work, medicine, and emergencies.
Marie Curie: The physicist and chemist who pioneered research on radioactivity and discovered polonium and radium. Her work established radioactivity as a measurable property of elements.

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