Radiation vocabulary becomes easier when each quantity is kept separate. Activity describes how often unstable nuclei disintegrate; exposure describes ionization produced in air; absorbed dose describes energy deposited per unit mass; and equivalent or effective dose applies radiation and tissue weighting to express potential biological effect. The unit names can appear together in one report, but they answer different questions and cannot be substituted for one another.
Activity: Becquerels and Curies
The becquerel (Bq) is one nuclear disintegration per second. The curie (Ci) is a much larger historical unit: 1 Ci = 3.7 × 10¹⁰ Bq, based on the activity of radium-226. Use the Radiation Activity Converter to compare Bq, kBq, MBq, and Ci values while preserving the fact that activity says nothing by itself about absorbed dose or biological risk.
Exposure and Absorbed Dose
Exposure in air can be reported in coulombs per kilogram or roentgens; 1 R = 2.58 × 10⁻⁴ C/kg of air. Absorbed dose is measured in gray (Gy), where 1 Gy = 1 J/kg, and rad, where 1 rad = 0.01 Gy. The Radiation Exposure Converter and Radiation Absorbed Dose Converter keep those dimensions separate so a student does not accidentally apply an exposure factor to an absorbed-dose value.
Why Gray and Sievert Are Not a Direct Swap
The sievert (Sv) and rem describe dose equivalent or related weighted quantities, not simply absorbed dose in every situation. Although 1 rem = 0.01 Sv as a unit conversion within that quantity, translating a measured absorbed dose in Gy to a biological-effect quantity requires radiation type and, where applicable, tissue weighting. There is no universal Gy-to-Sv multiplier. The Radiation Converter is therefore for unit-family reference, not a clinical or medical dosing decision.
A Safe Study Workflow
Begin by writing the measured quantity beside the number: activity, exposure, absorbed dose, or equivalent dose. Convert only within that family, retain the source, isotope, radiation type, geometry, and measurement conditions, and ask a qualified health physicist or clinician about real-world interpretation. The conversion factors in this educational guide follow the U.S. Department of Health and Human Services REMM reference table; they are not a substitute for calibrated instrumentation, regulatory guidance, or professional medical advice.