Radioactivity Unit Converter (Becquerel ↔ Curie)

Units of Radioactivity Radioactivity is measured in units of activity — the number of nuclear decays (disintegrations) per unit time. Becquerel (Bq): 1 disintegration per second. The SI unit, adopted in 1975. Named after Henri Becquerel who discovered radioactivity in 1896 in France. Curie (Ci): 3.7 × 10¹⁰ disintegrations per second = 37 GBq. Originally defined as the activity of 1 gram of radium-226. The Curie was defined in honor of Marie and Pierre Curie, who isolated radium in 1898 in France.

Unit Relationships 1 Ci = 3.7 × 10¹⁰ Bq = 37 GBq (exact by definition) 1 mCi = 3.7 × 10⁷ Bq = 37 MBq 1 µCi = 3.7 × 10⁴ Bq = 37 kBq 1 Rutherford (Rd) = 10⁶ Bq = 1 MBq (obsolete) 1 dpm (disintegrations per minute) = 1/60 Bq ≈ 0.01667 Bq

Activity of Common Sources 1 gram of Ra-226: 1 Ci (37 GBq) — the definition of the Curie. 1 gram of C-14: ~4.46 × 10⁹ Bq ≈ 120 mCi. Human body (from K-40 and C-14): ~8,000 Bq naturally. Typical nuclear medicine dose (Tc-99m for SPECT): 500–1000 MBq (13–27 mCi). Chernobyl cesium-137 release: estimated 85 PBq (petabecquerel = 10¹⁵ Bq). Background radiation rate indoors: ~0.1–1 µSv/h (depending on location and radon levels).

Activity-to-Mass Relation A = N × λ = (m × N_A / M) × (ln2 / t½) Where N = number of atoms, N_A = Avogadro’s number (6.022×10²³ /mol), M = molar mass (g/mol), t½ = half-life. Long-lived isotopes: very low activity per gram (U-238 half-life = 4.47 × 10⁹ years → ~12,400 Bq/g). Short-lived isotopes: high activity per gram (I-131 half-life = 8.02 days → ~4.6 × 10¹⁵ Bq/g).

Why Activity Matters Higher activity = more radiation emitted per second = more biological dose per second. Activity decreases exponentially: A(t) = A₀ × e^(−λt) = A₀ × 2^(−t/t½). This is why nuclear waste remains hazardous for thousands of years — long-lived isotopes maintain activity for geological timescales. Medical radioisotopes are chosen for short half-lives to minimize long-term patient exposure.

Dose vs Activity Activity (Bq or Ci) measures decays per second — not the energy deposited in tissue. Absorbed dose (Gray, Gy) = energy per unit mass. Effective dose (Sievert, Sv) = biological effect considering radiation type. Converting from activity to dose requires knowledge of the particle type, energy, and geometry.