According to a release, as part of the Comprehensive Nuclear Test Ban Treaty Organization's International Monitoring System (IMS), DOE also maintains the capability to detect tiny quantities of radioisotopes that might indicate an underground nuclear test on the other side of the world. These detectors are extremely sensitive and can detect minute amounts of radioactive materials.
The release indicates that on March 18, one of the monitoring stations in Sacramento, California that feeds into the IMS detected "miniscule quantities" of iodine isotopes and other radioactive particles that "pose no health concern at the detected levels." Collectively, the agencies said the levels amount to a level of approximately 0.0002 disintegrations per second per cubic meter of air (0.2 mBq/m3). Specifically, the level of Iodine-131 was 0.165 mBq/m3, the level of Iodine-132 was measured at 0.03 mBq/m3, the level of Tellurium-132 was measured at 0.04 mBq/m3, and the level of Cesium-137 was measured at 0.002 mBq/m3.
Similarly, between March 16 and 17, a detector at DOE's Pacific Northwest National Laboratory in Washington State detected trace amounts of Xenon-133, which is a radioactive noble gas produced during nuclear fission that poses no concern at the detected level. The levels detected were approximately 0.1 disintegrations per second per cubic meter of air (100 mBq/m3).
The doses received by people per day from natural sources of radiation -- such as rocks, bricks, the sun and other background sources -- are 100,000 times the dose rates from the particles and gas detected in California or Washington State. These types of readings remain consistent with our expectations since the onset of this tragedy, and are to be expected in the coming days. The release indicates that following the explosion of the Chernobyl plant in Ukraine in 1986 -- the worst nuclear accident in world history -- air monitoring in the United States also picked up trace amounts of radioactive particles, less than one thousandth of the estimated annual dose from natural sources for a typical person.