Which of the following is NOT a source of man-made radiation?

Radon gas is naturally occurring and is a result of the decay of uranium found in soil, rock, and water. It is a radioactive gas that can accumulate in buildings, particularly in confined areas such as basements. Since radon is found in nature and is not a product of human activity, it is classified as a natural source of radiation.

In contrast, X-rays, tanning beds, and lasers are all forms of man-made radiation. X-rays are produced by equipment that generates radiation to create images for diagnostic purposes in medicine. Tanning beds emit ultraviolet radiation to induce tanning in the skin, while lasers are devices that produce intense beams of light through a process of optical amplification. Each of these examples involves technology and human intervention, distinguishing them as sources of artificial or man-made radiation.

Identifying radon gas as a natural source helps emphasize the distinction between natural and artificial sources of radiation, which is crucial for understanding radiation protection principles in dental and medical practice.