Which of the following is a type of ionization chamber?

• A. thermoluminesent dosimeters (TLD)
• B. optically stimulable luminescent dosimeter (OSL)
• C. high-purity germanium detector
• D. Geiger (GM) counter

Answer: (D)

The key idea here is how ionization chambers work: radiation ionizes gas inside a chamber and the resulting ions are collected by an electric field to produce a measurable current, which is proportional to the radiation dose rate.

Among the options, the Geiger-Müller counter uses a gas-filled tube where incoming radiation ionizes the gas and the ensuing charge is collected to generate pulses. This is the type of detector based on ionization in a gas, i.e., an ionization chamber in its broad sense. The other devices rely on different mechanisms: thermoluminescent dosimeters (TLD) and optically stimulated luminescent dosimeters (OSL) measure dose by trapped energy that is released as light, not continuous ionization current, and a high-purity germanium detector is a semiconductor detector that measures charge from radiation interactions in a crystal, not in a gas-filled chamber.