What characterizes natural radiation?

Natural radiation is characterized by the emission of energy as a result of the decay of unstable atoms. This process, known as radioactive decay, involves the transformation of unstable atomic nuclei into more stable forms, emitting radiation in the form of alpha particles, beta particles, or gamma rays. This type of radiation can occur in various natural materials, such as rocks, soil, and even certain gases in the atmosphere.

The other choices do not accurately depict natural radiation. Producing radiation deliberately for medical procedures pertains to artificial or man-made sources used in diagnostics and treatments, which is unrelated to the natural occurrence of radiation. Suggesting that natural radiation comes solely from man-made substances contradicts its definition, as it originates from naturally occurring radioactive materials found in the environment. While it is important to protect living tissues from excessive radiation exposure, it cannot be classified as completely harmless. Certain levels of natural radiation can have biological effects, depending on the dose and duration of exposure. Therefore, the correct choice highlights the intrinsic process of decay that defines natural radiation.