As the public searches for answers about radiation from Japan’s growing nuclear crisis reaching the United States, they are turning to the Environmental Protection Agency’s RadNet Central Data Exchange, which makes nationwide radiation levels available multiple times a day. But the data requires expert interpretation and could further confuse and worry novices trying to use the system.
RadNet is a large network of highly sensitive radiation monitors – two of which are positioned in San Francisco and San Jose – that record various isotope levels in the air and express them in Gamma Energy Ranges. Those ranges do not easily translate into useful information for the public because they must be converted into sieverts, a unit used by medical experts to determine the impact of radiation on humans.
The scattered graph shows a portion of the isotope data collected between March 12 and March 18 by the EPA's RadNet radiation monitoring device in San Francisco. On March 18 there is a minute rise above the area's normal radiation levels.
The scattered graph shows a portion of the isotope data collected between March 12 and March 18 by the EPA's RadNet radiation monitoring device in Colorado Springs. The normal daily level of radiation in Colorado Springs is more than double the Bay Area's, an indicator that the slight increase in radiation seen in the Bay Area on Friday is not dangerous to human health.
“There isn’t a simple conversion between the two,” said UC Berkeley nuclear engineering professor Peter Hosemann.”But the data is useful because we can see when the cloud is here.”
The United Nations reported on Tuesday that a plume of radiation from Japan would reach the West Coast by Friday afternoon, but that the radiation would be diluted to harmless levels during its 5,000 mile journey across the Pacific Ocean.
Hosemann agreed that the level of radiation would not endanger people even though RadNet will detect it.
“In the next couple days, we’ll see an increase in radiation levels by a factor of 2 or 3,” Hosemann said. “Just because you can measure a change, doesn’t make dangerous.”
Looking at the San Francisco data around 3:30 p.m. this afternoon, Hosemann wrote, “It appears there is a trend upward today, 150 points higher than yesterday at the same time. This could be the first indication that the stuff is now here. The levels are still only half of what Colorado Springs has as a natural background. I would say if we don’t see an increase by 1,000 there is nothing to worry about.”
A two to three fold increase in Bay Area Gamma Energy Ranges, whose proximity to the coast makes them naturally low, would raise isotope levels to the typical, year-round level in Colorado Springs. The RadNet monitors are so sensitive, Hosemann said, they register nuclear weapons testing in North Korea.
“Chernobyl lead to a factor of 10 increase here,” Hosemann said about the Bay Area.
The EPA and Department of Energy released a statement this afternoon stating that a monitoring station in Sacramento had detected a tiny increase in the radioactive isotope xenon-133 and that they had traced it to the Fukushima reactors in Japan.
They characterized the increase as “approximately one-millionth of the dose rate that a person normally receives from rocks, bricks, the sun and other natural background sources.” A similar increase of the isotope was detected two days ago in Washington State on March 16 and 17.
A certain level of isotopes are always present in the air, water, and food supply, and scientists refer to this as the “background” level, or a baseline from which to measure any increase. A look at the historical RadNet data establishes a normal background range for the Bay Area.
According to the EPA website, the agency reviews RadNet data before making it public. “Radiation emergency response experts can request access to a restricted RadNet data site, where all RadNet data is housed before being released for public access.”
