What instrument is used to measure exposure at 90 degrees to the patient at a distance of 1 meter?

• A. Geiger-Muller counter
• B. Ionization chamber
• C. Dosimeter badge
• D. OSL

Answer: (B)

When you need a measured exposure rate in air at a specific distance from a source (such as scatter radiation at 90 degrees from the patient at 1 meter), use an instrument that converts ionization in air into an electrical signal for an immediate readout. An ionization chamber does exactly that: it contains a known volume of air, collects the ion pairs created by the incident X-ray photons, and provides a direct measure of exposure (air kerma) at that location. This makes it well-suited for quantifying the scatter dose at a set distance and angle, with good energy response across diagnostic X-ray energies and a rapid, quantitative readout.

Geiger-Muller counters aren’t ideal for this purpose because they are better for detecting discrete radiation events and have limited, energy-dependent response and accuracy at low scatter dose rates. Dosimeter badges and OSL dosimeters measure accumulated dose over time and are worn on or near the body, not used to report instantaneous exposure at a fixed position in space. They don’t provide the immediate exposure-rate data needed for evaluating scatter at a specific distance and angle.