Which of the following units measures radiation exposure equivalent?

The millirem is a unit used to measure radiation exposure in terms of the biological effect that different types of radiation have on human tissues. It is a derived unit from the rem (Roentgen Equivalent Man), which factors in the type of radiation and its potential harm to biological organisms.

In contexts involving radiation safety and exposure, the millirem specifically quantifies the amount of radiation dose received, considering the varying sensitivity of different tissues and the type of radiation, such as alpha, beta, and gamma radiation. Therefore, it provides a meaningful way to gauge risk and formulate safety protocols.

While the other options, like microrem and RAD, are also related to measuring radiation, they do not directly convey the concept of biological effect as effectively as the millirem. The microrem is simply a smaller subdivision of the rem, and while the RAD measures absorbed radiation dose, it does not directly incorporate the quality factor needed to assess biological impact, making it less relevant when discussing equivalent exposure. Parts per billion is used in measuring concentrations or contamination levels, not radiation exposure. Thus, the millirem is the most suitable choice for measuring radiation exposure equivalent in terms of biological effects.