A principle(s) for effecting external radiation protection is (are):

In the realm of radiation protection, several principles are employed to effectively safeguard individuals from external radiation exposure. The correct answer encompasses all of these principles—distance, shielding, and time of exposure—as each plays a crucial role in minimizing radiation risks.

Distance is fundamental; increasing the distance between a radiation source and a person significantly reduces the radiation exposure due to the inverse square law. This principle suggests that as one moves further away from a radiation source, the intensity of exposure diminishes rapidly.

Shielding involves using barriers made from materials that can absorb or deflect radiation, thereby reducing the amount that reaches an individual. Different types of radiation require different kinds of shielding; for instance, lead is effective against gamma rays, while concrete may be more appropriate for neutron radiation. By incorporating appropriate shielding materials, exposure can be considerably lowered.

The time of exposure is another critical factor. The less time spent near a radiation source, the lower the dose of radiation received. This principle is straightforward—minimizing the duration of exposure directly correlates to reducing the amount of radiation absorbed by an individual.

By utilizing all three principles—distance, shielding, and time—radiation protection strategies become much more effective in safeguarding individuals from harmful radiation exposure. Hence, acknowledging all these methods