Exam category: Safety → Radiation Physics and Radiobiology
Why it matters: Every dose figure you will read at work, from a fluoroscopy dose display to your dosimetry report, is stated as one of these quantities, each with its own unit. The registry tests what each quantity measures, its unit, and which one fits a given scenario.
There's a chain: how much radiation is in the air (air kerma) → how much energy a specific tissue actually absorbs (absorbed dose) → how biologically damaging that absorbed dose is for that tissue, accounting for radiation type (equivalent dose) → how much whole-body risk that represents once you account for which organs were exposed and how sensitive they are (effective dose). Each step adds a layer of "how much this actually matters," not just "how much radiation was there."
Air kerma is the kinetic energy photons transfer to electrons during ionization — radiation intensity measured in air. Unit: gray in air (Gya).
Before air kerma, this same "how much ionization in the air" idea was called exposure: the amount of ionization x-rays or gamma rays produce in a mass of air. Its unit is the coulomb per kilogram (C/kg), the electrical charge liberated per kilogram of air.
Exposure is defined only for air and only for x-rays/gamma rays. Modern practice reports air kerma (Gy) instead, so treat C/kg as the older name for that same first link in the chain.
Memory cue — read the unit: C/kg is charge per kilogram of air, so it can only be exposure. Every other quantity in this lesson is a gray or a sievert.
Answer this to keep going. 6 more sections unlock below.
A survey record lists a reading in C/kg. Which quantity is that unit reporting?
Section 1 of 7. Answer the check to keep going.