Radiation Activity Conversion Calculator

The curie was introduced in 1910 as a practical unit tied to radium experiments. The becquerel was adopted as the SI unit in 1975, named after Henri Becquerel who discovered radioactivity in 1896. Both remain in use because the curie is entrenched in US nuclear medicine practice, while the becquerel is the international scientific standard.

Diagnostic radiopharmaceutical activities vary by procedure: Tc-99m scans use 185–1110 MBq (5–30 mCi), FDG-PET scans use 370–740 MBq (10–20 mCi), and I-131 thyroid therapy can use 1.85–7.4 GBq (50–200 mCi). Therapeutic applications use higher activities than diagnostic ones.

Activity alone does not determine hazard. The radiation dose depends on the type of emissions (alpha, beta, gamma), their energies, the distance from the source, shielding, and exposure duration. A 1 Ci alpha source inside a sealed container may be far less hazardous externally than a 1 mCi unshielded gamma source. Dose calculations require additional information beyond activity.

Specific activity is the activity per unit mass (Bq/g or Ci/g) of a radioactive substance. It depends on the isotope's half-life: shorter half-lives yield higher specific activities. For example, Co-60 has a specific activity of about 1131 Ci/g, while U-238 has only 0.33 μCi/g due to its 4.5-billion-year half-life.

Activity concentrations (Bq/L, Bq/kg, pCi/L) use the same Bq-Ci conversion factors applied to the activity numerator. For example, the US EPA drinking water limit of 5 pCi/L equals $$5 \times 3.7 \times 10^{-2} = 0.185$$ Bq/L. Simply convert the activity portion and keep the per-unit denominator unchanged.