Radiation-Activity Converter

Radiation activity is the rate at which a radioactive substance undergoes nuclear decay — how many unstable atomic nuclei in a sample break down per unit of time. A higher activity means more decays happen each second, corresponding to a stronger, more intensely radioactive source. Activity is a property of the sample itself, independent of any shielding, distance, or exposure — it doesn't tell you how much radiation a person nearby would actually receive, only how "hot" the source is.

Our Radiation-Activity converter supports the SI unit, becquerel (Bq), defined simply as one nuclear decay per second, along with its metric multiples from millibecquerel up through terabecquerel. The curie (Ci), the older traditional unit, remains extremely common in nuclear medicine, industry, and older regulatory documents throughout the US and elsewhere; it was originally defined as the activity of exactly one gram of radium-226, which works out to almost exactly 3.7 × 10¹⁰ decays per second. The converter includes the curie's full range from kilocurie down to picocurie, plus the rutherford (an obsolete but occasionally still-referenced unit equal to one million decays per second), and disintegrations per second or minute, the units used directly in radiation counting and detector calibration.

To use the converter, select your starting and target units from the dropdown lists and enter a value — the result is calculated instantly to up to 12 significant digits. For example, converting a typical diagnostic nuclear medicine dose of 10 millicurie to becquerel gives 370,000,000 Bq (370 MBq), a conversion needed constantly when comparing US clinical practice (which still largely uses curies) against international literature and regulatory standards (which use becquerels).

Radiation activity conversions are essential in nuclear medicine (specifying diagnostic and therapeutic radioisotope doses, such as iodine-131 for thyroid treatment or technetium-99m for imaging), industrial applications (radiography sources, gauging instruments, and smoke detectors), nuclear power and research (characterizing fuel, waste, and reactor materials), and radiation safety regulation (activity limits define how sources must be transported, stored, and disposed of). Because activity alone doesn't determine biological risk — that depends on the type of radiation, the exposure pathway, and the resulting absorbed dose — activity conversions are typically just the first step in a larger radiation safety calculation involving the Radiation Absorbed Dose and Radiation Exposure converters elsewhere in this section.

All conversion factors used in this tool are drawn from standard, internationally recognized unit definitions, so results are dependable for nuclear medicine dosing, radiation safety compliance, and regulatory reporting. The converter is free, requires no account, and works equally well on desktop and mobile devices.