What is the relationship between Bq and Ci? How many Becquerels equal 1 Curie?
1 Ci (Curie) = 3.7×10¹⁰ Bq (Becquerel) = 37,000,000,000 Bq = 37 GBq (gigabecquerel). This is an exact defined value with no approximation. Conversion formulas: Bq = Ci × 3.7×10¹⁰; Ci = Bq ÷ 3.7×10¹⁰. Bq is the SI international unit, named after French physicist Henri Becquerel (discoverer of natural radioactivity); Ci is the traditional unit, named after Marie Curie, originally defined as the activity of 1 gram of radium-226 (1910), and precisely redefined as 3.7×10¹⁰ Bq by the International Committee for Weights and Measures in 1953.
How do kBq, MBq, and Bq convert?
Bq (Becquerel) is the base unit: 1 kBq (kilobecquerel) = 10³ Bq = 1,000 Bq; 1 MBq (megabecquerel) = 10⁶ Bq = 1,000,000 Bq = 1000 kBq; 1 GBq (gigabecquerel) = 10⁹ Bq; 1 TBq (terabecquerel) = 10¹² Bq. Note that this tool supports 4 units: Bq, kBq, MBq, and Ci. Larger GBq/TBq and smaller mCi/μCi must be converted to the nearest supported unit first, then scaled by factors of 1000. For example, 1 mCi = 0.001 Ci = 37 MBq, 1 μCi = 0.000001 Ci = 37 kBq.
How much radioactivity is injected for a PET-CT scan?
PET-CT examinations commonly use F-18 FDG (fluorodeoxyglucose) imaging agent. The typical injected activity for adults is approximately 185–555 MBq (i.e., 5–15 mCi), or about 3.7–5.2 MBq/kg (0.1–0.14 mCi/kg) by body weight. Imaging occurs about 1 hour after injection. The physical half-life of F-18 is approximately 109.8 minutes; after 10 half-lives (~18 hours), residual activity in the body drops below 1/1024 of the initial amount. PET myocardial perfusion using Rb-82 requires higher activity (~1110–2220 MBq per scan), but its half-life is only 75 seconds, resulting in lower patient radiation dose.
How many Bq are in natural background radiation? Is it harmful?
Natural background radiation levels: airborne radon and its progeny are the main source. Typical indoor radon concentration is 10–100 Bq/m³ (Chinese standard limit: 100 Bq/m³ annual average, action level 300 Bq/m³); terrestrial gamma dose rate is approximately 50–200 nSv/h; natural potassium-40 in the human body is about 4000–5000 Bq (~70,000 decays per minute); natural radionuclide activity in food is tens to hundreds of Bq per kilogram. The global average natural background radiation is about 2.4 mSv/year, which is a normal exposure level and does not cause health hazards.
What activity/dose is used in radiotherapy?
External beam radiotherapy (linear accelerators) uses MV-level X-ray beams, not sealed radioactive source activity, but rather the dose unit Gy (Gray), with typical curative radiotherapy doses of 60–70 Gy. Brachytherapy (afterloading) uses Ir-192 sources (activity ~370 GBq = 10 Ci) or Cs-137 sources. Iodine-131 therapy for hyperthyroidism typically uses oral activity of 370–555 MBq (10–15 mCi); thyroid cancer ablation doses can reach 3.7–7.4 GBq (100–200 mCi). This tool provides activity conversion; for absorbed dose/dose equivalent, please use the radiation dose converter.
What is half-life? How does it relate to activity?
Half-life (T½) is the time required for a radionuclide's activity to decay to half its initial value. Decay law: A(t) = A₀ × (1/2)^(t/T½) = A₀ × e^(-λt), where λ = ln2/T½ is the decay constant. Note: half-life is an intrinsic property of each nuclide, independent of temperature, pressure, or chemical form. Common nuclide half-lives: F-18 ~109.8 minutes, Tc-99m ~6 hours, I-131 ~8 days, Ir-192 ~74 days, Co-60 ~5.27 years, Cs-137 ~30 years, Ra-226 ~1600 years, U-238 ~4.5 billion years. Nuclides with the same activity but different half-lives have completely different total atom counts and radiation hazard durations.
What activity levels are used for industrial radiography sources?
Industrial radiography (non-destructive testing) commonly uses Ir-192 gamma sources with activity of about 1.85–3.7 TBq (50–100 Ci); Co-60 sources can reach 370 TBq (10,000 Ci). Industrial level/density gauges using Cs-137 or Co-60 sources typically have lower activity (~0.1–10 GBq = several mCi to hundreds of mCi). These activity levels are high-hazard sources and must be managed per radiation safety regulations. China classifies radioactive sources into Categories I–V: Category I extremely high hazard (≥1×10¹⁴ Bq Co-60 or equivalent), Category II high hazard (≥1×10¹² Bq), Category III hazard (≥1×10¹⁰ Bq), Category IV low hazard (≥1×10⁸ Bq), Category V very low hazard (<1×10⁸ Bq).
What is the difference between radioactivity and radiation dose (Sv/Gy)?
Activity (Bq/Ci) describes how many decays per second a source emits — the source's 'strength'; absorbed dose (Gy/Gray) describes how much radiation energy is absorbed per unit mass of matter (1 Gy = 1 J/kg); equivalent dose (Sv/Sievert) is the biologically weighted dose accounting for different radiation types (gamma/beta radiation: 1 Gy = 1 Sv; alpha radiation: 1 Gy = 20 Sv). The three cannot be directly converted — different nuclides with the same activity produce vastly different doses due to differences in radiation type, energy, and half-life. This tool only converts activity (Bq/Ci); for dose conversion, please use the radiation dose unit converter.
What are mCi and μCi? How do they relate to Ci in this tool?
mCi (millicurie) and μCi (microcurie) are subunits of the Curie (Ci): 1 mCi = 0.001 Ci = 3.7×10⁷ Bq = 37 MBq; 1 μCi = 0.000001 Ci = 3.7×10⁴ Bq = 37 kBq. Nuclear medicine clinics commonly use mCi (e.g., 10 mCi FDG injection = 370 MBq); environmental samples commonly use μCi or Bq. This tool supports Ci; for mCi conversion, divide the value by 1000 before converting to Ci, then multiply the result by 1000 to get mCi. Similarly, GBq = 1000 MBq, TBq = 1000 GBq.
How much radioactivity do nuclear power plants release during normal operation?
Radioactive releases from nuclear power plants via gaseous and liquid pathways during normal operation are strictly regulated: China's GB 6249 sets limits for gaseous tritium emissions from nuclear power plants at approximately 1.5×10¹³ Bq/year (per million kilowatts), liquid tritium at approximately 7.5×10¹³ Bq/year; noble gases (e.g., Kr-85) at approximately 1.5×10¹⁶ Bq/year. However, after dilution through atmosphere/water bodies, the annual additional dose to the public is far below natural background (typically <0.01 mSv/year, less than ~0.5% of background). Note: large total activity does not mean high dose; it must be assessed comprehensively considering dilution factors, nuclide types, and exposure pathways.
Why is food labeled in Bq/kg? How is radioactive contamination detected?
Radionuclide activity concentration in food is measured in Bq/kg, i.e., how many decays per second per kilogram of food. China's food safety standard (GB 14882) sets Cs-137 limits for general foods at 100–1000 Bq/kg (depending on food category and nuclide); guidance levels for gross alpha/beta activity concentration in drinking water are 0.5 Bq/L and 1 Bq/L. After the Fukushima accident, foods in some areas were restricted due to Cs-137 exceeding limits. Food radioactivity testing typically uses high-purity germanium (HPGe) gamma spectrometers for nuclide identification and quantification; samples require preprocessing and are measured for hours to days.
Which radioactivity units does this tool support? How to distinguish from dose units?
This radioactivity converter supports 4 units: Bq (Becquerel), kBq (kilobecquerel), MBq (megabecquerel), and Ci (Curie). Note that these are 'activity' units representing decays per second from a source, not dose units. For radiation dose units (Gy Gray, Sv Sievert, rem, Rad), please use the radiation dose converter; radiation exposure (R Roentgen) is also outside the scope of this tool. Simple distinction: activity describes source strength, dose describes radiation energy received by people/matter.
