 A basic fallout shelter consists of shields that reduce gamma ray exposure by a factor of 1000.The required shielding can be accomplished with 10 times the thickness of any quantity of material capable of cutting gamma ray exposure in half.Shields that reduce gamma ray intensity by 50% (1/2) include 1 cm (0.4 inch) of lead, 6 cm (2.4 inches) of concrete, 9 cm (3.6 inches) of packed earth or 150 m (500 ft) of air.