Which instrument measures gamma inside the body?

• A. Whole body counters— amount/type of radioactivity (gamma)
• B. Thermoluminescent dosimeters
• C. Survey meters
• D. Pocket dosimeters

Answer: (A)

Measuring gamma radiation inside the body relies on detecting gamma photons emitted by radionuclides that are located within tissues. A whole-body counter is specifically designed for this purpose: it uses detectors placed around or near the person to noninvasively count the gamma rays coming from inside the body, giving an activity measurement for gamma-emitting contaminants. This directly assesses internal contamination and the associated internal dose from substances like cesium-137 or iodine-131.

Thermoluminescent dosimeters, by contrast, are worn on the body to record the total external radiation dose a person receives over time; they don’t detect radioactive emissions from inside the body. Survey meters are used to survey the environment or surfaces for gamma radiation and are not suited to gauge internal contamination. Pocket dosimeters measure real-time external exposure at work, again reflecting external dose rather than internal activity.