Position of Free Air Dose Percentage Lead Shield Average Decrease No lead shield 3.0 x [10.sup.-4] mGy 0% (baseline) Shadow shield (lead placed on crib) 2.6 x [10.sup.-4] mGy 13% Contact shield (lead placed over testes) 1.6 x [10.sup.-4] mGy 46%
Position of Free Air Dose Percentage Lead Shield Average Decrease No lead shield 3.0 x [10.sup.-4] mGy 0% (baseline) Shadow shield (lead placed on crib) 2.8 x [10.sup.-4] mGy 17% Contact shield (lead placed over testes) 1.4 x [10.sup.-4] mGy 59%
Air dose rates varied from one to 10 microsieverts ([micro]Sv) per hour, results that coincided closely with airborne monitoring of Fukushima conducted by the U.S.
Unlike heavy metals that stick around forever, radioactive elements decay, so it is hardly surprising that weekly measurements since May 2011 by the Japanese Nuclear Regulation Authority (NRA) have shown gradual declines in air dose rates in the 20-kilometer evacuation zone around the power plant.