Which of these is not a basic principle of radiation protection ?
Justification
Collimation
Limitation
Optimization
In addition to the three basic principles of radiation protection (justification, limitation, and optimization), one  can apply the following additional techniques to reduce the radiation burden to the patient:

Collimation of the x-ray beam.
Correct focus-to-skin distance.
Lead apron with thyroid collar.
More radiation-sensitive image receptors.