What does the term 'rad' refer to?

The term 'rad' refers to a measure of energy absorbed from ionizing radiation. Specifically, it is defined as the absorption of 0.01 joules of energy per kilogram of matter. This unit is used in radiology and radiation protection to quantify the amount of radiation energy that is deposited in a given mass of tissue. Understanding the rad is crucial for assessing potential biological effects from radiation exposure and is foundational in the field of health physics.

The other choices refer to different concepts: sound exposure is measured in decibels; chemical concentration is often expressed in terms such as molarity or parts per million; and permissible exposure limits are established based on various regulations but do not directly relate to the unit 'rad'.