ADAA Intro to Basic Concepts in Dental Radiology Practice Test

The main idea here is distinguishing between the different categories of radiation in dental radiography. The radiation that comes directly from the X-ray tube toward the patient is the primary radiation. It is the useful beam produced at the focal spot and before any interaction with matter, so it hasn’t yet been altered by tissues. Once this primary beam hits the patient, interactions within the tissues generate secondary radiation, including scatter. The remnant radiation refers to what exits the patient toward the image receptor, which includes transmitted primary photons and secondary photons produced inside the tissues. So the radiation that strikes the patient directly from the tube is primary radiation.