Scattered radiation is caused by interaction of the primary radiation with matter. The interaction with matter could cause a change in direction (scattering) and a reduction in energy.
From a radiation protection point of view, scattered radiation is assumed to come primarily from interactions of primary radiation with tissues of the patient.

Scattering refers to the reflection of radiation, electromagnetic or particulate, when interacting with matter. Scattering results in a loss of energy of the radiation.
Backscattering refers to a reflection of radiation in a direction generally greater than 90 degrees to that of the incident radiation.

Different types of screens are used in medical imaging. The intensifying screen or a pair of screens is used with x-ray film in radiography. Fluorescent screens coated with phosphor crystals emit light when exposed to radiation.

The second is the SI unit of time. Definition: The length of time taken for 9192631770 periods of vibration of the caesium-133 atom.

Secondary radiation is the result of absorption of other radiation in matter. It could be either electromagnetic or particulate in nature.