Which of the following is a common source of ionizing radiation?

Cosmic rays are considered a common source of ionizing radiation because they are high-energy particles that originate from outer space and can penetrate the Earth's atmosphere. These rays consist primarily of protons and other atomic nuclei that have enough energy to ionize atoms, which is a key characteristic of ionizing radiation. This means when cosmic rays interact with matter, they can displace electrons from atoms, leading to ionization that poses potential health risks.

In contrast, ultraviolet light, while it can also cause ionization at very high energies, is not typically classified as a common source of ionizing radiation when compared to cosmic rays. Infrared radiation and radio waves are forms of non-ionizing radiation, which do not possess sufficient energy to ionize atoms or molecules and thus are not considered sources of ionizing radiation. Understanding the distinction between these types of radiation is crucial for recognizing potential health implications in radiation protection practices.