radioactive

Radioactive describes atoms with unstable nuclei that spontaneously decay to more stable configurations, emitting ionizing radiation in the process. This instability arises from an imbalance of nuclear forces or excess energy in the nucleus.

Radioactive materials occur naturally in the earth and atmosphere, and can also be produced in laboratories or reactors. Each isotope has a characteristic half-life, the time required for half of a sample to decay.

The radiation released may be alpha particles, beta particles, gamma rays, or, in some cases, neutrons. Alpha radiation consists of helium nuclei and is highly ionizing but poorly penetrating. Beta radiation is lighter and penetrates more, while gamma rays are highly penetrating electromagnetic radiation.

Shielding and detection are tailored to the radiation type. Alpha particles are stopped by a sheet of paper, beta by plastic or metal, while gamma rays and neutrons require dense shielding such as lead, concrete, or specialized materials. Detection methods include Geiger counters and semiconductor detectors that measure radiation activity and energy.

Measurements use the becquerel, equivalent to one decay per second, with the curie as a historical unit. Absorbed dose is measured in gray, and the biologically effective dose in sievert.

Applications include medicine (imaging and radiotherapy), industry (non-destructive testing and tracers), energy (nuclear power), and dating methods (radiocarbon dating). Exposure to ionizing radiation can damage cells and increase cancer risk, so safety standards, monitoring, and regulatory controls are essential in handling radioactive materials.