What is the approximate range of low-energy gamma rays in air?

• A. About 3 kilometers
• B. About 3 meters
• C. About 3 centimeters
• D. About 30 meters

Answer: (B)

The main idea is attenuation of gamma rays as they travel through air. As gamma photons pass through air, they interact with air molecules and their intensity drops with distance. For low-energy gamma rays, the probability of interaction per unit length is relatively high, so the photons don’t travel far before being absorbed or scattered.

Because air is not dense, the range isn’t enormous, but it isn’t tiny either. The attenuation behaves such that a noticeable drop in flux occurs over only a few meters, giving a practical range on the order of a few meters. In this context, about 3 meters is a reasonable, commonly cited estimate for low-energy gamma rays in air.

Higher-energy gamma rays penetrate farther because their interactions per meter are less probable, while much lower-energy photons would be absorbed over shorter distances. Among the options, the range around 3 meters best matches the typical attenuation length for low-energy gamma rays in air.