What is the unit of measure of ionization in air due to the passage of gamma or x-radiation?

The correct unit of measure for ionization in air caused by the passage of gamma or X-radiation is the Roentgen. This unit specifically quantifies the amount of ionization in air produced by X-rays or gamma rays. One Roentgen is defined as the amount of radiation that produces one electrostatic unit of charge in one cubic centimeter of air.

Using the Roentgen as a measure is essential in radiation safety and dosimetry, as it provides a way to gauge the potential biological effects of radiation exposure based on the amount of ionization occurring in a given volume of air. This measurement is particularly relevant in industrial radiography, where understanding the ionizing radiation levels is crucial for ensuring both personnel and public safety.

The other options do not apply to the measurement of ionization caused by radiation. Inches and pressure per square inch relate to distance and force, respectively, rather than radiation, while protons per atom pertains to atomic structure and does not provide any relevant information regarding the effects of ionization due to radiation.