RICHLAND -- Additional minute quantities of radiation linked to failed nuclear reactors in Japan have been detected by Pacific Northwest National Laboratory in Richland.
However, no radiation levels of concern have been detected anywhere in the United States, including Richland, according to the Environmental Protection Agency and the Department of Energy.
The first radiation in the continental United States from the Japan crisis was detected by PNNL on Wednesday. DOE said xenon 133 has been detected at 0.1 disintegrations per second per cubic meter of air.
"The levels of xenon 133 that PNNL detected were extremely low and pose no health hazard," PNNL said in a statement. The radioactivity detected is at a tiny fraction of what a person receives each day from natural background sources, such as the sun, according to PNNL.
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DOE and EPA described the amount of radiation received by people by natural sources as 100,000 times the amount in the particles and gas detected in Richland.
Since Wednesday, levels of slightly higher xenon have been measured, but they still are significantly below levels of concern to public health, according to PNNL.
Friday sensors also showed the presence of iodine isotopes, but at even lower levels than the xenon, according to PNNL.
The xenon will continue to migrate across the world, becoming even more dilute, and will decay away into stable elements, according to PNNL.
PNNL ruled out any local sources for the radioactive isotopes detected, such as the nuclear power plant near Richland. Lab scientists also are confident the isotopes are coming from Japan because they are consistent with isotopes detected in Japan, and they are consistent with calculations of where experts expected them to travel.
"These types of readings remain consistent with our expectations since the onset of this tragedy and are to be expected in the coming days," said DOE and EPA in a joint statement.
PNNL detected the isotopes through a continuous, ultra-sensitive monitoring system it operates as a result of its research and development on methods to detect very low levels of nuclear releases. The work includes the development of the world's most sensitive sensors that are being used worldwide to detect airborne radiological debris for treaty verification and monitoring.
PNNL operates similar sensors in 70 locations around the world. In the United States, is has sensors in California, Hawaii, Kansas and Alaska.