Becquerel to Curie Converter
Quickly convert from Becquerel to Curie.
How to convert
Formula:
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Radioactivity is measured by the rate at which unstable atomic nuclei decay — emitting alpha, beta, or gamma radiation.
Where is it used?
• Nuclear Medicine — Radiopharmaceuticals administered to patients are dosed in megabecquerels (MBq) or millicuries (mCi); for example, a typical thyroid scan uses 185–370 MBq of technetium-99m.
Examples:
• 1 curie (Ci) = 3.7 × 10¹⁰ becquerels (Bq)
• 1 millicurie (mCi) = 3.7 × 10⁷ Bq (37 MBq)
Radioactivity is measured by the rate at which unstable atomic nuclei decay — emitting alpha, beta, or gamma radiation. The SI unit is the becquerel (Bq), defined as one nuclear disintegration per second. The older curie (Ci), still common in medical and industrial contexts, equals 3.7 × 10¹⁰ Bq — the activity of one gram of radium-226. Understanding activity units is essential for radiation safety, nuclear medicine dosimetry, and environmental monitoring.
Radioactive activity quantifies how many nuclear decay events occur per unit time in a radioactive material. Higher activity means more decays per second and therefore more radiation emitted. The becquerel (Bq) and curie (Ci) are the primary activity units; the rutherford (Rd) — 10⁶ Bq — and disintegrations per minute (dpm) are used in specialist laboratory contexts. Activity differs from dose: a high-activity source does not necessarily deliver a high dose to a person, because dose also depends on radiation type, energy, and geometry.
Where is it used?
- Nuclear Medicine — Radiopharmaceuticals administered to patients are dosed in megabecquerels (MBq) or millicuries (mCi); for example, a typical thyroid scan uses 185–370 MBq of technetium-99m.
- Radiation Safety & Regulation — National regulators (NRC, IAEA) set exemption limits and transport thresholds in becquerels or curies; materials above set Bq limits require licensing and labelled packaging.
- Environmental Monitoring — Radon gas in homes is measured in becquerels per cubic metre (Bq/m³); the EU reference level is 300 Bq/m³ for existing buildings.
- Radiochemistry & Tracer Studies — Specific activity (Bq/g or Ci/mol) describes how radioactive a given mass of material is, critical for designing tracer experiments in biochemistry and pharmacokinetics.
Common Conversion Mistakes
Confusing activity with dose
Activity (Bq or Ci) measures how many decays occur per second; it does not tell you the biological effect on a person. Dose (gray, sievert) accounts for the energy deposited and the type of radiation. A material with very high activity can deliver a low dose if the radiation is weakly penetrating or the source is far away.
Misapplying the curie prefix scale
The curie is a large unit: 1 Ci = 3.7 × 10¹⁰ Bq. Common medical and lab quantities are millicuries (mCi) or microcuries (μCi). Forgetting the prefix and treating 1 mCi as 1 Ci overstates the activity by a factor of 1,000 — a potentially dangerous error in dose calculations.
Ignoring half-life when comparing activities
A 1 Bq sample of a short-lived isotope (seconds half-life) contains very few atoms, while 1 Bq of a long-lived isotope (billions of years) contains an enormous number of atoms. Activity and the number of radioactive atoms are related through the half-life: A = λN = (ln 2 / t½) × N. Comparing activities of isotopes with very different half-lives without this context is misleading.
Confusing becquerel with gray or sievert
The becquerel (Bq) measures activity — how many decays per second. The gray (Gy) measures absorbed dose — energy deposited per kilogram. The sievert (Sv) measures equivalent dose — biological effect. These are distinct physical quantities. A high-activity source does not automatically imply high absorbed dose or high biological risk, because dose also depends on radiation type, energy, shielding, geometry, and distance.
Quick Reference Table
| From | To |
|---|---|
| 1 curie (Ci) | 3.7 × 10¹⁰ becquerels (Bq) |
| 1 millicurie (mCi) | 3.7 × 10⁷ Bq (37 MBq) |
| 1 microcurie (μCi) | 37,000 Bq (37 kBq) |
| 1 rutherford (Rd) | 1,000,000 Bq (1 MBq) |
| 1 becquerel (Bq) | 1 disintegration per second (dps) |
| 1 Bq | 60 disintegrations per minute (dpm) |
| 1 Ci | 2.22 × 10¹² dpm |
Frequently Asked Questions
What is a becquerel and why was it introduced?
The becquerel (Bq) was adopted as the SI unit of radioactivity in 1975 to replace the curie, which is defined relative to radium-226 — a historical artefact. One becquerel equals exactly one nuclear disintegration per second, giving a clean, dimensionally transparent unit. It was named after Henri Becquerel, who discovered radioactivity in 1896.
How do I convert curies to becquerels?
Multiply curies by 3.7 × 10¹⁰ to get becquerels. To convert becquerels to curies, divide by 3.7 × 10¹⁰. Example: 5 mCi = 5 × 10⁻³ Ci × 3.7 × 10¹⁰ = 1.85 × 10⁸ Bq = 185 MBq. In nuclear medicine software, MBq and mCi appear side by side because US practice still uses curies while international practice uses SI.
What is specific activity?
Specific activity is the activity per unit mass (Bq/g) or per unit amount of substance (Bq/mol). It depends on the isotope's half-life and atomic mass. Short-lived isotopes have very high specific activity — carbon-11 (t½ = 20 min) has a specific activity around 3.4 × 10¹⁷ Bq/g, while uranium-238 (t½ = 4.5 Gyr) has only ~12,400 Bq/g. High specific activity is valued in tracer studies to achieve detectable signals with tiny masses.
What household radioactivity levels are considered safe?
Background radiation from natural sources typically produces exposures of 1–3 mSv/year. Radon in homes: the WHO recommends action above 100 Bq/m³; the EU reference level is 300 Bq/m³. Smoke detectors contain ~37 kBq (1 μCi) of americium-241, which is safe in normal use. Bananas contain ~15 Bq of potassium-40 each, giving rise to the informal 'banana equivalent dose' as a relatable reference point.
Sources & Standards
- IAEA Safety Glossary: Terminology Used in Nuclear Safety and Radiation Protection (2018 edition)
- NIST SP 811 — Guide for the Use of the International System of Units (SI)
- WHO Handbook on Indoor Radon (2009)
- ICRP Publication 107 — Nuclear Decay Data for Dosimetric Calculations
Reviewed by The Unit Hub Editorial Team · March 2026