There are three ways for a person to reduce their exposure to radiation. One is time. A person can reduce exposure by reducing the amount of time exposed to the radiation. Exposure is often cumulative, so reducing the time reduces the cumulative exposure. Another way is distance. Radiation strength dies off proportionally to the square of the distance from the source, so even a small distance added makes a big difference in exposure levels. The third way is shielding. Adding or increasing the mass of shielding between a person and the radiation source can greatly reduce their exposure. The type of shielding required greatly depends on the type of radiation. Some forms of radiation can be effectively stopped with water. Others require lead shielding.