Final answer:
The exposure factor that primarily controls the quantity of x-rays produced is milliamperage (mA), which determines the flow of electrons and the resulting production of x-ray photons.
Step-by-step explanation:
The exposure factor that primarily controls the quantity of x-rays produced is mA (milliamperage). The mA level controls the number of electrons available to produce x-rays, which directly influences the quantity of x-ray photons generated. Higher mA settings increase the electron flow, resulting in a higher yield of x-ray photons, whereas lower mA settings decrease the number of electrons and, correspondingly, the production of x-rays is reduced.
kVp (kilovoltage peak) affects the quality or energy of the x-rays produced, not the quantity. SID (Source-to-Image Distance) affects the intensity of the radiation at the image receptor by the inverse square law, whereas time alone would influence the total amount of radiation by prolonging exposure, provided all other factors are remaining constant.