Radioactivity Converter
Inputs
| Becquerel | 37,000,000,000 Bq |
|---|
Radioactivity Converter
Convert radioactivity between becquerels (Bq), curies (Ci), and SI-prefixed multiples (kBq, MBq, GBq, mCi, µCi).
SI Units
Traditional Units
Radioactivity
Radioactivity is the spontaneous emission of radiation from unstable atomic nuclei. Each time a nucleus decays, it emits energy as alpha particles, beta particles, or gamma rays, and transforms into a more stable nuclide. The activity of a radioactive sample is the rate at which these decays occur — more decays per second means higher activity.
Units of radioactivity
Becquerel (Bq) — the SI unit, defined as exactly one nuclear decay per second. The becquerel replaced the curie in scientific and regulatory use after the 1975 SI update. Small amounts of radioactivity in food, water, and building materials are routinely reported in Bq or kBq.
Kilobecquerel (kBq) — 1,000 Bq. The americium-241 source inside a household ionization smoke detector has an activity of about 37 kBq (1 µCi).
Megabecquerel (MBq) — 10⁶ Bq. The standard unit for nuclear medicine. A typical adult PET scan dose is 300–400 MBq of fluorine-18 (FDG). 1 MBq = 1/37 mCi ≈ 0.02703 mCi.
Gigabecquerel (GBq) — 10⁹ Bq. Used for therapeutic doses and industrial sources. A thyroid cancer treatment with iodine-131 may use 3–7 GBq (80–200 mCi).
Curie (Ci) — the historical unit, defined as the activity of one gram of radium-226: exactly 3.7 × 10¹⁰ Bq. It was introduced in 1910 by Marie Curie's colleagues and remained the primary unit in medicine and industry until the SI transition. Many US regulations and medical protocols still express doses in mCi.
Millicurie (mCi) — 10⁻³ Ci = 3.7 × 10⁷ Bq = 37 MBq. The most common unit for diagnostic radiopharmaceuticals. A bone scan uses about 20 mCi of technetium-99m.
Microcurie (µCi) — 10⁻⁶ Ci = 3.7 × 10⁴ Bq = 37 kBq. Used for laboratory sources and sealed check sources.
Key conversion table
| From | To Bq | To mCi |
|---|---|---|
| 1 Ci | 3.7 × 10¹⁰ | 1,000 |
| 1 mCi | 3.7 × 10⁷ | 1 |
| 1 µCi | 3.7 × 10⁴ | 0.001 |
| 1 GBq | 10⁹ | 27.03 |
| 1 MBq | 10⁶ | 0.02703 |
| 1 kBq | 10³ | 2.703 × 10⁻⁵ |
The central conversion factor is 1 Ci = 3.7 × 10¹⁰ Bq (exact by definition). A handy shortcut: 1 mCi = 37 MBq and 1 µCi = 37 kBq.
Activity vs. dose
Activity (Bq or Ci) measures how many decays occur per second. It does not measure biological harm. Whether a given activity is dangerous depends on:
- Isotope — the type of radiation (alpha, beta, gamma) and the decay energy
- Exposure pathway — external exposure, inhalation, or ingestion
- Duration — how long the exposure lasts
The gray (Gy) measures absorbed energy per kilogram of tissue; the sievert (Sv) weights that by radiation type to estimate biological risk. National and international regulators (ICRP, IAEA, NRC) set dose limits in Sv, not Bq.
Usage
Enter any value in any field. All other units update automatically. For example, type 10 in the mCi field to instantly see 370 MBq, 0.37 GBq, 0.01 Ci, and 3.7 × 10⁸ Bq.
Frequently Asked Questions (FAQ)
What is the difference between becquerel and curie?
Both measure radioactivity (the rate of nuclear decays), but they differ in scale and origin. The becquerel (Bq) is the SI unit — 1 Bq = 1 decay per second. The curie (Ci) is an older unit defined as the activity of one gram of radium-226, equal to exactly 3.7 × 10¹⁰ Bq. Because the curie is so large, medical professionals often work in millicuries (mCi) or microcuries (µCi), while research increasingly uses MBq or GBq.
What does becquerel actually measure?
A becquerel measures the rate of radioactive decay in a sample: 1 Bq means exactly one nucleus disintegrates per second, emitting radiation (alpha, beta, or gamma). It does not measure the energy or biological effect of the radiation — that requires the gray (Gy) or sievert (Sv). A higher becquerel count simply means more decays per second, which is useful for comparing source strengths or calculating dose rates.
How do I convert MBq to mCi?
Divide MBq by 37 to get mCi: 1 mCi = 37 MBq. For example, a PET scan dose of 370 MBq equals exactly 10 mCi. The conversion factor 37 comes from 1 Ci = 3.7 × 10¹⁰ Bq, so 1 mCi = 3.7 × 10⁷ Bq = 37 MBq.
What activity levels are considered safe?
Safety depends on the type of radiation, the isotope, and exposure duration — not activity alone. That said, some reference points: the activity in a household ionization smoke detector is about 1 µCi (37 kBq) of americium-241, sealed inside and posing no health risk.
Diagnostic nuclear medicine doses typically range from 100–400 MBq (3–10 mCi). Background radiation in the body (mostly from potassium-40 and carbon-14) amounts to roughly 4,000–8,000 Bq. Regulatory limits and safety assessments are set by national radiation protection authorities and the IAEA.
Disclaimer
Conversion factors are exact per BIPM definition: 1 Ci = 3.7 × 10¹⁰ Bq. This tool converts units of activity only — it does not calculate dose, dose rate, or biological risk.
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