Radioactivity Converter: Becquerel, Curie, and Rutherford

The becquerel (Bq) is the SI unit of radioactivity, defined as one nuclear disintegration per second. It measures the rate at which a radioactive substance undergoes radioactive decay, not the energy or biological impact of the emitted radiation. One becquerel is an extremely small quantity; environmental and medical measurements often use kilobecquerels (kBq), megabecquerels (MBq), or gigabecquerels (GBq). The becquerel replaced the curie as the preferred scientific unit following adoption of the International System of Units.

The curie (Ci) is an older unit of radioactivity defined as the activity of one gram of radium-226: exactly 3.7 x 10^10 disintegrations per second, or 37 gigabecquerels (GBq). It was named after Marie and Pierre Curie. Although the becquerel is now the SI standard, the curie remains widely used in the United States for industrial, medical, and regulatory applications. Millicuries (mCi) and microcuries (µCi) are common in nuclear medicine dosing.

The rutherford (Rd) is a non-SI unit of radioactivity equal to one million disintegrations per second, or 10^6 Bq, making it equivalent to one megabecquerel (MBq). It was named in honour of physicist Ernest Rutherford and was proposed as a practical intermediate unit between the very small becquerel and the very large curie. The rutherford is rarely used today in scientific or regulatory contexts, having been largely superseded by SI prefixed becquerel units.

Radioactivity measures the rate of nuclear decay (disintegrations per second, in becquerels or curies). Radiation dose measures the energy deposited in tissue by the emitted radiation. A substance can be highly radioactive yet pose minimal dose risk if the radiation is easily shielded or travels only a short distance. Conversely, even modest activity from alpha-emitting isotopes ingested into the body can deliver a significant biological dose. Dose equivalent is measured in sieverts (Sv) or rem, and absorbed dose in grays (Gy) or rad.

Many common materials contain trace radioactivity. A typical banana contains about 15 Bq from potassium-40. The average human body contains roughly 7,000 Bq from potassium-40 and about 3,000 Bq from carbon-14. Smoke detectors contain a small sealed source of americium-241, typically around 30,000 Bq (30 kBq). Dental X-ray film contains very small amounts. Background radiation contributes approximately 0.1 to 0.2 µSv/hr in most locations, and the average person receives about 2 to 3 mSv per year from natural sources.