The roentgen is a measure of ionization in air produced by exposure to which types of radiation?

The roentgen is specifically defined as a unit that measures the exposure to ionizing radiation, particularly the ionization of air. It quantifies the amount of ionization produced in air when it is subjected to X-rays or gamma rays, which are forms of electromagnetic radiation. When X-rays or gamma rays pass through air, they interact with air molecules, causing ionization, which is what the roentgen measures.

This makes the selection of X rays or gamma rays as the correct answer appropriate, as the roentgen quantifies the effects of these types of radiation on air. In contrast, while alpha and beta particles can also produce ionization, they do so in different contexts and are not measured in roentgens, as this unit specifically relates to air ionization caused by high-energy photons such as X-rays and gamma rays. Neutrons, although capable of causing ionization through secondary processes, do not fit the definition as strictly as X rays or gamma rays do when it comes to measuring in roentgens.