Which statement about gamma dose rate constant is true?

• A. It relates dose rate to energy of gamma photons alone.
• B. It is independent of distance.
• C. It applies only to alpha emitters.
• D. It relates dose rate at a distance to the source's activity and gamma energy, and is used to estimate shielding.

Answer: (D)

The gamma dose rate constant links how the dose rate at a given distance from the source depends on the source’s activity and the energy of the emitted gamma photons, and it’s used to estimate shielding needs. It’s defined for a specific gamma energy and often quoted as the dose rate at a reference distance (like 1 meter) per unit activity; the actual dose rate at other distances follows the inverse-square relationship for an unshielded point source, and shielding introduces attenuation that depends on gamma energy. This makes the statement that it relates dose rate at a distance to the source’s activity and gamma energy, and is used to estimate shielding, the best description.