☢️ Radioactivity Conversion Calculator 2026
Convert between becquerel (Bq), curie (Ci), millicurie (mCi), microcurie (µCi), gigabecquerel (GBq), terabecquerel (TBq), rutherford (Rd) and all SI prefix variants instantly. Essential reference for nuclear medicine, health physics, environmental monitoring, and radiation safety professionals — with MathJax decay law formulas, specific activity calculations, and a 2500+ word nuclear science guide.
📊 All Units — Simultaneous Conversion
📖 How to Use This Radioactivity Converter
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1Filter by Unit Family (Optional)
Click a category button — All Units, Becquerel (Bq), Curie (Ci), or Other — to filter the unit dropdowns to the relevant subset. Nuclear medicine typically uses MBq and mCi; environmental monitoring uses Bq and kBq; industrial radiography uses GBq to TBq. Filtering makes finding the right unit much faster when working within a single unit system.
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2Enter Your Activity Value or Use a Preset
Type the numeric activity value in the Value field. Accepts scientific notation format. Or click any Quick Preset — human body background radiation (7,000 Bq), smoke detector Am-241 source (30 kBq), PET scan F-18 dose (400 MBq), iodine-131 therapy dose (3.7 GBq), or the benchmark 1 curie definition (37 GBq).
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3Select From and To Units
Choose source unit (e.g., curie for historic specifications, MBq for nuclear medicine, pCi for air quality measurements) and target unit. Over 27 units cover all practical ranges from femtocurie (fCi, sub-atomic trace analysis) to yottabecquerel (YBq, cosmological scales). All SI-prefix Bq variants use exact powers of 10.
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4Read Simultaneous Results for All Units
The green result box shows the primary conversion. The scrollable "All Units" panel simultaneously shows your value in every unit in the selected category — essential for radiation safety reports, nuclear medicine prescription conversion, or academic papers that require multi-unit verification.
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5Apply the Decay Law and Specific Activity Formulas
Use the MathJax formula section to calculate how activity changes over time (radioactive decay law: A(t) = A₀ × 2^(-t/t½)), predict when a source will decay to a safe level, or compute the specific activity of a pure radioisotope from its half-life and atomic mass.
📐 Radioactivity Formulas — MathJax Rendered
\[ N(t) = N_0 \cdot e^{-\lambda t} \quad \text{(number of radioactive atoms at time } t \text{)} \]
\( N_0 = \) initial atom count · \( \lambda = \) decay constant (s⁻¹) · \( t = \) elapsed time (s)
\[ A(t) = A_0 \cdot e^{-\lambda t} = A_0 \cdot 2^{-t/t_{1/2}} \quad \text{(activity at time } t \text{)} \]
\( A_0 = \) initial activity (Bq or Ci) · \( t_{1/2} = \) half-life · \( \lambda = \) decay constant
\( A = \lambda \cdot N = \frac{\ln 2}{t_{1/2}} \cdot N \quad \text{(activity in Bq)} \)
\( t_{1/2} = \frac{\ln 2}{\lambda} = \frac{0.6931}{\lambda} \quad \text{(half-life from decay constant)} \)
\( \text{Activity remaining: } A(n) = A_0 \cdot \left(\frac{1}{2}\right)^n \quad (n = \text{number of half-lives elapsed}) \)
\( \text{Time for activity to fall to fraction } f: \; t = t_{1/2} \cdot \frac{\ln(1/f)}{\ln 2} \)
\[ A_s = \frac{N_A \cdot \ln 2}{t_{1/2} \cdot M_r} \quad \text{(Bq/g)} \]
\( N_A = 6.02214076 \times 10^{23} \text{ mol}^{-1} \) (Avogadro's number) · \( M_r = \) molar mass (g/mol) · \( t_{1/2} = \) seconds
\( \text{Example (Ra-226): } A_s = \frac{6.022 \times 10^{23} \times 0.6931}{(1600 \times 3.156 \times 10^7) \times 226} = 3.66 \times 10^{10} \text{ Bq/g} \approx 1 \text{ Ci/g} \)
\( \text{Inverse: mass from activity: } m = \frac{A}{A_s} \text{ (grams)} \)
\( 1 \text{ Ci} = 3.7 \times 10^{10} \text{ Bq} \quad \text{(exact, by definition)} \)
\( 1 \text{ Bq} = \frac{1}{3.7 \times 10^{10}} \text{ Ci} = 2.\overline{702} \times 10^{-11} \text{ Ci} \)
\( 1 \text{ mCi} = 3.7 \times 10^7 \text{ Bq} = 37 \text{ MBq} \quad 1 \text{ µCi} = 3.7 \times 10^4 \text{ Bq} = 37 \text{ kBq} \)
\( 1 \text{ Rd (rutherford)} = 10^6 \text{ Bq} = 1 \text{ MBq} = \frac{1}{37,000} \text{ Ci} \)
📊 Complete Radioactivity Conversion Reference Table
| Unit | Symbol | In Becquerel (Bq) | In Curie (Ci) |
|---|---|---|---|
| Yottabecquerel | YBq | 10²⁴ | 2.703 × 10¹³ Ci |
| Zettabecquerel | ZBq | 10²¹ | 2.703 × 10¹⁰ Ci |
| Exabecquerel | EBq | 10¹⁸ | 2.703 × 10⁷ Ci |
| Petabecquerel | PBq | 10¹⁵ | 27,027 Ci |
| Terabecquerel | TBq | 10¹² | 27.03 Ci |
| Gigabecquerel | GBq | 10⁹ | 0.02703 Ci = 27.03 mCi |
| Megabecquerel | MBq | 10⁶ | 2.703 × 10⁻⁵ Ci = 27.03 µCi |
| Kilobecquerel | kBq | 10³ | 2.703 × 10⁻⁸ Ci = 27.03 nCi |
| Becquerel | Bq | 1 | 2.703 × 10⁻¹¹ Ci |
| Millibecquerel | mBq | 10⁻³ | 2.703 × 10⁻¹⁴ Ci |
| Microbecquerel | µBq | 10⁻⁶ | 2.703 × 10⁻¹⁷ Ci |
| Megacurie | MCi | 3.7 × 10¹⁶ | 10⁶ Ci |
| Kilocurie | kCi | 3.7 × 10¹³ | 10³ Ci |
| Curie | Ci | 3.7 × 10¹⁰ | 1 Ci (definition) |
| Millicurie | mCi | 3.7 × 10⁷ = 37 MBq | 10⁻³ Ci |
| Microcurie | µCi | 3.7 × 10⁴ = 37 kBq | 10⁻⁶ Ci |
| Nanocurie | nCi | 37 Bq | 10⁻⁹ Ci |
| Picocurie | pCi | 0.037 Bq = 37 mBq | 10⁻¹² Ci |
| Femtocurie | fCi | 3.7 × 10⁻⁵ Bq = 37 µBq | 10⁻¹⁵ Ci |
| Rutherford | Rd | 10⁶ = 1 MBq | 1/37,000 Ci |
🌍 Real-World Radioactivity Reference Values
| Source / Material | Activity (Bq) | Activity (Ci/mCi) | Context |
|---|---|---|---|
| 🧬 Human body (K-40, C-14) | ~7,000 Bq | ~189 nCi | Natural — always present |
| 🔥 Smoke detector (Am-241) | ~30,000 Bq (30 kBq) | ~0.81 µCi | Alpha emitter in sealed source |
| 📺 Old colour TV (K-40 in glass) | ~10 Bq | ~270 pCi | Trace natural potassium |
| 💊 Thyroid uptake scan (I-123) | ~7.4 MBq | ~200 µCi = 0.2 mCi | Nuclear medicine diagnostic |
| 🩺 Bone scan (Tc-99m) | ~740 MBq | ~20 mCi | Most common nuclear medicine scan |
| 🏥 PET scan (F-18 FDG) | ~400 MBq | ~10.8 mCi | Oncology / neurology PET imaging |
| 💊 I-131 thyroid therapy | 1–7.4 GBq | 27.5 mCi – 200 mCi | Treatment of hyperthyroidism / thyroid cancer |
| 🔬 Ra-226 (1 gram) | 37 GBq | 1 Ci (definition) | Original curie definition base |
| 🏭 Industrial radiography (Ir-192) | 1–5 TBq | 27–135 Ci | NDT weld inspection, regulated sealed source |
| ⚛️ Nuclear reactor (total core) | ~3 × 10¹⁸ Bq (3 EBq) | ~80 MCi | Operating power reactor core fission products |
| 🌋 Chernobyl release (1986) | ~5 × 10¹⁸ Bq | ~85 MCi released | Largest accidental release; per UNSCEAR 2008 |
| 🌾 Banana (K-40 per kg) | ~130 Bq/kg | ~3.5 nCi/kg | Natural food radioactivity |
| 🪨 Granite rock (U/Th/K) | ~1,000 Bq/kg | ~27 nCi/kg | Natural building material radioactivity |
| 🌊 Seawater (U-238, Ra-226) | ~12 Bq/L | ~324 pCi/L | Dissolved natural radionuclides |
| 🌬️ Indoor radon (US average) | ~50 Bq/m³ | ~1.35 pCi/L | EPA action level: 148 Bq/m³ (4 pCi/L) |
⚛️ Understanding Radioactivity Units
Becquerel (Bq) — The SI Standard
The SI unit of radioactivity, adopted at the 15th CGPM in 1975. Defined as exactly 1 radioactive decay per second. Named after Henri Becquerel (1852–1908), who discovered radioactivity in 1896 when he found uranium salts exposed photographic plates without visible light — sharing the 1903 Nobel Physics Prize with Marie and Pierre Curie. The becquerel is extremely small: 1 Bq means only one atom decays per second. Environmental and medical contexts use kBq (thousands), MBq (millions), GBq (billions), and TBq (trillions).
Curie (Ci) — The Historical Unit
Defined in 1910 as the radioactivity of 1 gram of radium-226 = 3.7 × 10¹⁰ Bq exactly. Named jointly after Marie Curie (1867–1934) and Pierre Curie (1859–1906) — who jointly discovered polonium and radium in 1898. Still widely used in: US nuclear medicine dosing, NRC radiological materials licences, industrial sealed-source specifications, and environmental monitoring (picocuries per litre for radon gas in homes). The sub-units mCi (millicurie = 37 MBq) and µCi (microcurie = 37 kBq) are everyday clinical units in nuclear medicine.
Rutherford (Rd) — The Middle Unit
1 Rd = 10⁶ Bq = 1 MBq. Proposed in the 1940s–50s to provide a convenient intermediate-scale unit between the curie (too large) and the becquerel (too small). Named after Ernest Rutherford (1871–1937), who established the nuclear model of the atom and identified alpha and beta radiation types. The rutherford was never widely adopted and was superseded by megabecquerel (MBq) after SI standardisation. It appears only in historical nuclear physics literature from approximately 1946–1975.
Activity vs. Dose — Critical Distinction
Activity (Bq or Ci) = number of decays per second — it measures the source, not its effect on tissue. Absorbed dose (gray, Gy) = energy deposited per kg of tissue (1 Gy = 1 J/kg). Effective dose (sievert, Sv) = biologically weighted dose accounting for radiation type and organ sensitivity. Same activity → very different effective dose for different isotopes: 1 MBq of high-energy gamma emitter vs. 1 MBq of low-energy beta emitter can differ in effective dose by 100×. Unit conversion tools convert activity; dose assessment requires isotope-specific dosimetric models.
Picocurie (pCi) — Environmental Standard
1 pCi = 10⁻¹² Ci = 0.037 Bq. The picocurie per litre (pCi/L) is the US EPA and EU regulatory unit for measuring radon gas concentration in air. EPA action level: 4 pCi/L (148 Bq/m³) — at which point mitigation (sub-slab depressurisation) is recommended. The WHO guidelines use 100 Bq/m³ (2.7 pCi/L). Radon is the leading environmental cause of lung cancer after tobacco smoking (EPA: ~21,000 lung cancer deaths annually in the US). The picocurie per litre / becquerel per cubic metre conversion: 37 Bq/m³ = 1 pCi/L.
Nuclear Medicine Activity Units
Nuclear medicine uses MBq to GBq (SI) and mCi to Ci (US legacy). Common imaging doses: Tc-99m bone scan 740 MBq (20 mCi); F-18 PET scan 370–400 MBq (10–11 mCi); I-123 thyroid scan 7.4 MBq (200 µCi). Therapy doses: I-131 ablation 1.1–7.4 GBq (30–200 mCi); Lu-177 DOTATATE PRRT 7.4 GBq (200 mCi) per cycle. The 2013 IAEA Nuclear Medicine Physics handbook specifies dosimetry protocols for converting administered activity to organ absorbed dose using S-values (MIRD formalism) and patient-specific pharmacokinetics.
1 mCi = 37 MBq · 1 µCi = 37 kBq · 1 nCi = 37 Bq · 1 pCi = 37 mBq. This is because 3.7 × 10¹⁰ ÷ (10⁶ × 10³) = 37 exactly. Nuclear medicine dosimetrists use the "37 rule" to quickly cross-check Ci-to-Bq conversions mentally.
📚 Complete Guide to Radioactivity — Nuclear Physics, Units, and Real-World Applications
Radioactivity is one of the most profound discoveries in the history of science — and the correct conversion between its measurement units is essential for nuclear medicine dosing, radiation safety compliance, environmental monitoring, and industrial inspection. From the diagnosis of cancer with PET scans and the treatment of thyroid disease with iodine-131, to the regulation of radon gas in homes and the operation of nuclear power plants, every practical application of nuclear science requires fluent movement between becquerels (the SI unit), curies (the US/legacy unit), and their myriad SI-prefixed variants. Whether you need to convert a nuclear medicine prescription from mCi to MBq, check whether a radioactive material shipment exceeds an A2 transport quantity, or determine how long before a used Tc-99m generator reaches clearance level, this calculator provides the mathematical foundation.
Radioactivity was discovered by Henri Becquerel in 1896 — entirely by accident. Becquerel was studying phosphorescence in uranium salts, suspecting that sunlight exposure was needed for the fluorescence. He stored photographic plates and uranium samples in a drawer during an overcast period, expecting no reaction. When he developed the plates, he found they had been exposed anyway. Uranium was emitting penetrating radiation spontaneously, without any external energy input. This discovery shattered the classical physics assumption that atoms were immutable and stable. Within two years, Marie and Pierre Curie had isolated two new radioactive elements — polonium (named after Marie's native Poland) and radium — by processing tonnes of pitchblende ore. In 1910, the International Radium Standards Commission, chaired by Marie Curie, defined the curie as the radioactivity of exactly 1 gram of radium-226. Ernest Rutherford subsequently identified alpha and beta radiation types, established the nuclear model of the atom (1911), and proposed the proton (1919), earning his place as the father of nuclear physics.
The transition from curie to becquerel as the standard unit reflects the broader adoption of the SI system. The 15th General Conference on Weights and Measures (CGPM) formally adopted the becquerel in 1975, defined as 1 nuclear transformation (decay) per second, equal to 1 s⁻¹. The curie, while not an SI unit, remained (and remains) in widespread use in the United States — the NRC (Nuclear Regulatory Commission) licences specify quantities in curies, NCRP (National Council on Radiation Protection) reports often use curies, and nuclear medicine documentation in the US commonly lists doses in millicuries. The WHO, IAEA, and European regulatory framework mandates becquerels. This dual-system reality means that practitioners must convert fluently between the two: 1 mCi = 37 MBq, 1 µCi = 37 kBq, 1 Ci = 37 GBq — the factor 37 appears because the original radium experiment yielded 3.7 × 10¹⁰ Bq per gram.
In nuclear medicine, activity is the foundation of evidence-based dosing. EANM (European Association of Nuclear Medicine) dosimetry guidelines, the MIRD (Medical Internal Radiation Dose) Committee of the Society of Nuclear Medicine, and the IAEA Nuclear Medicine Physics handbook all specify administered activity as the primary treatment parameter. For diagnostic imaging, activities are standardised to deliver diagnostic-quality images while minimising radiation burden. Tc-99m (technetium-99m, t½ = 6.01 hours) is the workhorse of nuclear medicine — accounting for approximately 80% of all nuclear medicine procedures globally. Its short half-life means a 740 MBq (20 mCi) administered dose decays to below 12 MBq (0.3 mCi) within 48 hours — allowing patients to return home safely. F-18 (t½ = 110 minutes) used in PET scanning is even shorter-lived: a 370 MBq dose decays to under 1 MBq in 18 hours. The trend toward theranostics — using higher-activity doses of targeted radiopharmaceuticals like Lu-177 DOTATATE and Ac-225 PSMA agents — requires careful dosimetric planning in GBq ranges, with each cycle delivering 7.4 GBq (200 mCi) of lutetium.
Radiation protection and regulatory compliance depend critically on accurate activity quantification. The IAEA TECDOC-1539 and its successor, the IAEA Safety Standards SSR-6 (2018) for the transport of radioactive material, classify radioactive packages by "A1/A2 quantities" — activity thresholds (in TBq, GBq or mCi) that determine packaging required for transport. Package categories: Exempt (below clearance levels, typically kBq/MBq range), Type A (routine transport, GBq range), Type B (high-activity transport, TBq range), and Type C (air transport of exceptional quantities). An industrial iridium-192 radiography source of 3.7 TBq (100 Ci) is a Type B(U) package requiring a heavy steel certified container and full emergency response documentation. Understanding and converting between these activity thresholds is a daily responsibility for radiation safety officers and transport logistics managers. The EU Directive 2013/59/EURATOM establishes dose limits (20 mSv/year for occupational, 1 mSv/year for public) — relating activity to dose requires radioisotope-specific dose coefficients from ICRP Publication 119.
Environmental radioactivity measurement uses both Bq and pCi depending on regulatory jurisdiction. Radon in indoor air is the most common environmental radioactivity concern: radon-222 (t½ = 3.82 days), a noble gas produced by decay of uranium-238 in rock and soil, diffuses into buildings and undergoes alpha decay, depositing short-lived daughters (Po-218, Pb-214, Bi-214, Po-214) in lung tissue. The EPA recommends testing at or below 148 Bq/m³ (4 pCi/L) and mitigation above this level. European WHO guidance: 300 Bq/m³ reference level indoors. The conversion: 1 pCi/L air = 37 Bq/m³ (since 1 m³ = 1,000 litres and 1 pCi = 0.037 Bq). Drinking water radioactivity: EPA maximum contaminant levels are specified in pCi/L (e.g., 5 pCi/L for Ra-226+Ra-228 combined). Ground-level air radioactivity from nuclear weapons testing fallout isotopes (Cs-137, Sr-90) are measured in mBq/m³. Food radioactivity: EU Regulation 2016/52 sets maximum limits for food following nuclear accidents in Bq/kg.
Nuclear power generation involves the largest scales of radioactivity quantified anywhere outside stellar physics. The inventory of fission products in an operating 1 GWe (electric) light water reactor core is approximately 3–4 × 10¹⁸ Bq (3–4 EBq) — 100 million curies. Spent nuclear fuel immediately after removal from a reactor has activity ~1,000 times higher than average ore, dominated by short-lived fission products like I-131, Cs-137, and Sr-90. After 10 years of cooling, activity falls by approximately 1,000-fold due to decay of short-lived isotopes; after 1,000 years, only long-lived isotopes remain. The Chernobyl accident (1986) released approximately 5 × 10¹⁸ Bq (85 million curies) — the largest accidental radioactive release in history, per UNSCEAR 2008 Report. The Fukushima Daiichi accident (2011) released an estimated 5 × 10¹⁷ Bq (14 million curies) into the atmosphere, according to NISA estimates. These immense quantities require PBq (petabecquerel) and EBq (exabecquerel) units — scales natively handled by this converter.
❓ Frequently Asked Questions — Radioactivity Unit Conversion
What is radioactivity and how is it measured?
How do I convert curie to becquerel?
1 Ci = 37,000,000,000 Bq = 37 GBq
1 mCi = 37,000,000 Bq = 37 MBq
1 µCi = 37,000 Bq = 37 kBq
1 nCi = 37 Bq
1 pCi = 0.037 Bq = 37 mBq
The factor 37 appears at every level of SI prefix — making the "37 rule" the fastest mental conversion shortcut: nano-curies to becquerels × 37; micro-curies to kilo-becquerels × 37; milli-curies to mega-becquerels × 37.
How do I convert becquerel to curie?
1 GBq = 1/37 Ci = 27.03 mCi
1 MBq = 1/37,000 Ci = 27.03 µCi
1 kBq = 27.03 nCi
1 Bq = 27.03 pCi
In nuclear medicine, a quick check: if a dose is ~400 MBq, that's 400/37 ≈ 10.8 mCi — a typical PET scan F-18 FDG dose.
Why is 1 curie exactly 3.7 × 10¹⁰ Bq?
What is the difference between activity and dose?
Absorbed dose (gray, Gy = J/kg): Energy deposited per kg of tissue. Depends on activity, radiation type, energy, geometry, and tissue composition.
Effective dose (sievert, Sv): Biologically weighted absorbed dose, accounting for radiation type (alpha = 20× more damaging per unit energy than gamma) and organ sensitivity (bone marrow and lung are most radiosensitive). 1 Sv = 100 rem (legacy unit).
Same activity → very different effective dose depending on isotope: 1 MBq of Tc-99m (low energy gamma) gives ~7 mSv effective dose if ingested; 1 MBq of Po-210 (alpha emitter) gives ~500 mSv — 70 times higher.
What is half-life and how does it affect activity?
What is specific activity?
What is the radioactive decay law?
How much radioactivity is naturally in the human body?
What is radon and why is 4 pCi/L (148 Bq/m³) the action level?
What activity units are used in nuclear medicine?
United States (legacy): mCi and Ci. Same bone scan: "Administer 20 mCi Tc-99m MDP." Conversion: 740 MBq / 37 = 20 mCi ✓.
Common nuclear medicine activities: Tc-99m bone scan: 740 MBq (20 mCi) · F-18 PET: 370 MBq (10 mCi) · I-123 thyroid scan: 7.4 MBq (0.2 mCi) · Ga-68 PET: 185 MBq (5 mCi) · I-131 ablation: 1.1–7.4 GBq (30–200 mCi) · Lu-177 PRRT: 7.4 GBq (200 mCi) per cycle · Ra-223 therapy: based on body weight, ~55 kBq/kg (1.49 µCi/kg).