The roentgen is a measure of the ionization in air produced by exposure to __________.

The roentgen is a unit specifically used to measure the ionization produced in air by X-rays or gamma rays. It quantifies the amount of ionization that occurs when these forms of electromagnetic radiation interact with air, effectively allowing for an assessment of the radiation exposure. The roentgen focuses on the effects of high-energy photons, such as X-rays and gamma rays, which have the ability to ionize atoms in air, thereby creating free electrons and positively charged ions.

In contrast, alpha particles, beta particles, and neutrons interact with matter in different ways. Alpha particles, for example, have a low penetration ability and are primarily hazardous when ingested or inhaled, rather than being measured by their ionization in air. Beta particles can create ionization as well, but their measurement does not fit within the definition of roentgen, which is specific to electromagnetic radiation. Neutrons, being uncharged, also do not produce ionization in air in the same manner as X-rays or gamma rays, and their impact requires different measurement units, such as the neutron dose equivalent.

Thus, the definition and application of the roentgen make it clear that it directly relates to the ionization caused by X-rays or gamma rays, aligning