External doses can be the result of exposure to gamma, x ray, or high energy beta emitters.
Because radiation from low energy beta and alpha emitters do not penetrate the outer layer of skin, they present less of an external hazard, and internal exposure is the overriding concern. By reducing the amount of radioactive material used or lowering the settings on a radiation producing machine, dose can be reduced. The total dose received from an external source is dependent on the time of exposure to the source. Therefore, any time that is spent near a source should be controlled and used effectively. By increasing the distance between the source of exposure and an individual, the dose received can be significantly reduced.