Which of the following is NOT a common source of ionizing radiation?

Ultraviolet light is not considered a common source of ionizing radiation because it primarily falls within the non-ionizing portion of the electromagnetic spectrum. While ultraviolet light can cause damage to biological tissues, such as sunburn and skin cancer, it does not possess enough energy to ionize atoms or molecules, which is the defining characteristic of ionizing radiation.

In contrast, cosmic rays, radon gas, and medical procedures are established sources of ionizing radiation. Cosmic rays, which originate from outer space, consist of high-energy particles that can penetrate the Earth's atmosphere and reach the surface. Radon gas, a naturally occurring radioactive gas, is produced from the decay of uranium in soil and rock and is recognized as a significant indoor source of ionizing radiation. Additionally, certain medical procedures, such as X-rays and radiation therapy, intentionally use ionizing radiation for diagnostics and treatment.