Radiation Converter — Gy/rad, Sv/rem and Bq/Ci

Background.

Gray and sievert both work out to a joule per kilogram, yet a gray is not a sievert, and a converter that turned one into the other would be wrong in a way that matters. Radiation is described by three separate quantities, each with an SI unit and an older unit still common in American hospitals, labs and regulations: activity in becquerels or curies, absorbed dose in grays or rads, and equivalent dose in sieverts or rems. Within a quantity the conversion is exact arithmetic. Between quantities it is not a unit change at all. So the first choice here is the quantity, and the From and To menus then offer only its units; switch the quantity and both menus change with it.

The factors are set by definition. A rad is exactly 0.01 Gy and a rem exactly 0.01 Sv, so a gray is 100 rad and a sievert 100 rem. A curie is exactly 3.7 × 10¹⁰ Bq, which makes a millicurie 37 MBq and a microcurie 37 kBq. Each result also shows the value in the quantity's SI unit and a line repeating both units.

A converted number is the same measurement written differently. It carries no judgement about risk and is not a clinical interpretation or a regulatory assessment. Questions about a medical exposure belong with the treating clinician or a medical physicist, and workplace decisions with the licensed radiation-protection programme and its regulator.

What is radiation unit converter?

Activity is the rate at which a radioactive sample decays: one becquerel is one nuclear transformation per second, and the curie was originally tied to the activity of about one gram of radium-226. Absorbed dose is the energy ionising radiation deposits per unit mass of material: one gray is one joule per kilogram, and the older rad is 100 ergs per gram, or 0.01 Gy. Equivalent dose is absorbed dose multiplied by a radiation weighting factor that reflects how much biological harm each kind of radiation does, 1 for X-rays and gamma rays and 20 for alpha particles, and is expressed in sieverts or rem. The SI Brochure gives the gray and the sievert separate names so that the two are never confused.

How to use this calculator.

1. 01Under "Radiation quantity", choose what the number measures: absorbed dose for Gy or rad, equivalent dose for Sv or rem, radioactivity for Bq or Ci. A personal dosimeter report is normally in mSv or mrem, while a source or vial label is in MBq or mCi.
2. 02Enter the value; it can be zero or more.
3. 03Choose the From and To units. If a unit you expect is missing from the menus, the quantity is set wrong.
4. 04Millirem is not listed: 1 mrem is 0.01 mSv, or 0.001 rem, so convert it to one of those first.
5. 05Read the converted value with the SI value and the statement line, and copy the quantity name along with the number into any record.

The formula.

Each quantity has its own table of factors, each factor saying how many SI units one of that unit contains: target = value × SI-per(source) ÷ SI-per(target). For absorbed dose the factors are 1 for Gy, 0.001 for mGy, 0.000001 for µGy and 0.01 for rad. Equivalent dose follows the same pattern for Sv, mSv, µSv and rem. For activity they are 1 for Bq, 10³ for kBq, 10⁶ for MBq, 10⁹ for GBq, 3.7 × 10¹⁰ for Ci, 3.7 × 10⁷ for mCi and 3.7 × 10⁴ for µCi. All of these are exact definitions listed in NIST Special Publication 811, and the US Nuclear Regulatory Commission defines the same units in 10 CFR Part 20, so a conversion adds no uncertainty to the original figure.

A unit that is not in the chosen quantity's table is refused, which is what stops a gray-to-sievert request: with absorbed dose selected, Sv is simply not an absorbed-dose unit. Results are shown to ten decimal places. That is ample for doses, but a very small activity expressed in curies can fall below it, so tiny activities are better converted to microcuries.

A worked example.

Frequently asked questions.

References& sources.

1. [1]NIST SP 811 Appendix B.9 supplies rad-to-gray, rem-to-sievert and curie-to-becquerel factors.
2. [2]U.S. NRC 10 CFR Part 20 §§20.1004–20.1005 independently defines dose and activity units.
3. [3]BIPM SI Brochure assigns distinct special names to becquerel, gray and sievert to prevent quantity errors.