Radioactivity Converter

This radioactivity converter changes activity between becquerels, kilobecquerels, megabecquerels, gigabecquerels, curies, millicuries, microcuries and nanocuries. One becquerel is one decay per second, and one curie is exactly 3.7 × 10¹⁰ Bq, so 1 mCi = 37 MBq and 1 µCi = 37 kBq.

How to use the radioactivity converter

1. Enter the activity, for example 20 from a vial label in mCi.
2. In the radioactivity converter, choose its unit and the target unit, such as mCi to MBq.
3. Read the radioactivity converter result: 20 mCi = 740 MBq.

For Ci to Bq, multiply by 37,000,000,000. For Bq to Ci, divide by the same number. For mCi to MBq, multiply by 37.

What is radioactivity?

Radioactivity (activity) is the number of nuclear decays per second. The SI unit is the becquerel (Bq), one decay per second; the older curie (Ci) equals exactly 3.7 × 10¹⁰ Bq.

Conversion formula

The radioactivity converter stores every unit as a multiple of the base unit, the becquerel (Bq). To convert:

value in target unit = value × (factor of source unit ÷ factor of target unit)

where each factor is the size of the unit in becquerels.

Common radioactivity conversions

Radioactivity converter worked example

Convert 25 megabecquerels to millicuries:

1. Factor of MBq = 1,000,000 Bq
2. Factor of mCi = 37,000,000 Bq
3. 25 × 1,000,000 ÷ 37,000,000 = 0.6756757 mCi

Radioactivity unit reference

Reverse factors for each radioactivity unit

The reference table gives each unit in becquerels. To go the other way, divide by that factor; the list below does the division for you.

• Kilobecquerel (kBq), SI: 1 kBq = 1,000 Bq, so 1 Bq = 0.001 kBq.
• Megabecquerel (MBq), SI: 1 MBq = 1,000,000 Bq, so 1 Bq = 1 × 10⁻⁶ MBq.
• Gigabecquerel (GBq), SI: 1 GBq = 1 × 10⁹ Bq, so 1 Bq = 1 × 10⁻⁹ GBq.
• Curie (Ci), Traditional: 1 Ci = 3.7 × 10¹⁰ Bq, so 1 Bq = 2.7027 × 10⁻¹¹ Ci.
• Millicurie (mCi), Traditional: 1 mCi = 3.7 × 10⁷ Bq, so 1 Bq = 2.7027 × 10⁻⁸ mCi.
• Microcurie (µCi), Traditional: 1 µCi = 37,000 Bq, so 1 Bq = 2.7027 × 10⁻⁵ µCi.
• Nanocurie (nCi), Traditional: 1 nCi = 37 Bq, so 1 Bq = 0.02702703 nCi.

Curies and becquerels side by side

Because the curie is so large, practical values use prefixes on both sides:

A useful reverse rule: 1 MBq ≈ 27.03 µCi.

Activity changes with time

Activity falls as A = A₀ × (1/2)^(t / T½). Technetium-99m, widely used in medical imaging, has a half-life of about 6 hours, so 740 MBq (20 mCi) falls to 370 MBq after 6 hours and about 185 MBq after 12. Activity tells you how many decays occur, not the dose a person receives. Use the half-life calculator for decay and the sievert to rem converter for sieverts and rem.

Radon and smoke detectors

The US EPA action level for radon in homes is 4 pCi/L. The radioactivity converter turns that into 148 Bq/m³, since 1 pCi/L equals 37 Bq/m³. Many European countries set reference levels of 100 to 300 Bq/m³, so the figures are directly comparable once converted.

An ionization smoke detector usually holds about 1 µCi of americium-241, which is about 37 kBq. One curie is exactly 3.7 × 10¹⁰ Bq.

Older medical and lab records list source strengths in mCi or µCi. A 10 mCi dose of technetium-99m for a scan is 370 MBq, the figure used in most current hospital paperwork. Activity also falls over time with each half-life, so a stated value always belongs to a reference date.

Related converters and calculators

Related radiation tools:

• Half-life calculator: decay over time
• Sievert to rem converter: Sv and rem
• Absorbed dose converter: Gy and rad
• Radiation exposure converter: R and C/kg
• Scientific notation calculator: powers of ten

Sources

BIPM: SI Brochure; NIST Special Publication 811, Appendix B; US NRC Glossary: Curie.

Questions about this calculator