Radiation Converter (Activity)

The Radiation Activity Converter converts between units of radioactive activity, which measures the rate of radioactive decay (disintegrations per unit time). The SI unit is the becquerel (Bq), equal to one disintegration per second. The older unit is the curie (Ci), equal to 3.7 x 10¹⁰ Bq (37 billion disintegrations per second).

Radioactivity is measured in terms of how many atomic nuclei decay per unit time. The becquerel, named after Henri Becquerel who discovered radioactivity in 1896, is an extremely small unit — even a banana contains about 15 Bq of potassium-40. Practical sources used in medicine and industry are measured in megabecquerels (MBq) or gigabecquerels (GBq).

The curie, named after Marie and Pierre Curie, was originally defined as the activity of 1 gram of radium-226. It was later standardized as exactly 3.7 x 10¹⁰ disintegrations per second. The curie remains widely used in the United States and in medical physics, while the becquerel is the international standard.

Medical applications: a diagnostic thyroid scan uses about 5–30 MBq (0.1–0.8 mCi) of I-123, a PET scan uses 200–700 MBq (5–20 mCi) of F-18, and cancer radiotherapy sources may have activities of 100–500 TBq (3,000–15,000 Ci).

The converter also handles disintegrations per second (dps), which is numerically identical to becquerels, and disintegrations per minute (dpm), commonly used in laboratory scintillation counting.