Becquerels

The becquerel (symbol Bq) is the SI unit of radioactivity. It is defined as one disintegration per second, representing the rate at which a radioactive source undergoes decay. The unit is named after the French physicist Henri Becquerel, who discovered radioactivity in 1896. The becquerel became the SI unit of activity in the mid-20th century and is used to quantify how many atomic decays occur in a given time.

A key distinction is that the becquerel measures only the rate of disintegration, not the energy released or the biological effect. Therefore, it does not by itself indicate the hazard of a source. For context, the older unit curie (Ci) is still encountered in some settings: 1 Ci equals 3.7 × 10^10 Bq, and conversely 1 Bq equals about 2.7 × 10^-11 Ci. In practical applications, activity is often expressed in larger units such as megabecquerels (MBq) or gigabecquerels (GBq), especially for medical and industrial sources.

Activity changes over time as radioactive isotopes decay, following characteristic half-lives. Measurements of activity are performed with radiometric detectors that count decays or the emitted radiation. While activity reflects how many decays occur per second, assessments of radiation dose or risk typically involve additional quantities such as absorbed dose (gray) and equivalent dose (sievert), which account for energy deposition and biological effect.

Becquerels are widely used in nuclear medicine, environmental monitoring, industrial radiography, and research to express the strength of radioactive sources in a standardized, comparable way.