The Topic: Radiation Exposure.
The Question: How do scientists know what kind of (and how much) radiation exposure we do or do not face?
While we follow the news and expand our vocabulary to include the terms sievert (a somewhat fuzzy, composite unit of radiation), millisieverts, microsieverts (that’s millionths), Iodine-131, Cesium -137, and alpha, beta and gamma particles…
…a globally distributed network of super-sensitive radiation “sniffers” continuously monitors out planet’s air currents for minute traces of radioactive isotopes (radionuclides), included Iodine-131 and Cesium-137 — two isotopes released in some quantity following the explosions and malfunctions at the Fukushima Daiichi Nuclear Facility in Japan.
The current crop of sensors are all based on technology developed at Pacific Northwest National Laboratory (PNNL) in Richland, Washington (U.S.). These instruments were designed to detect secret nuclear bomb tests by other nuclear nations.
PNNL maintains/operates two such sensing instruments out of a global network* of 6o such detectors overseen by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), a United Nations organization based in Vienna, Austria.
View a GIF animation tracking the spread of radiation from the Fukushima accident (source: Austria’s Central Institute for Meteorology and Geodynamics).
Scientists at the CTBTO state that total radiation levels emitted by the Fukushima plant are approaching levels from the 1986 Chernobyl accident — though the level of highly dangerous radionuclides is vastly less, as there was no major explosion at the Japanese facility, like there was at Chernobyl, that could carry dense concentrations of particles high up into the atmosphere and spread them world-wide.
PNNL scientists estimate that the level of radiation making it to the U.S. is 17,000 times less than the normal, background radiation levels we are exposed to every day (which is about 8.5 microsieverts). PNNL shares its data with state and federal health agencies, which operate networks of less-sensitive detectors. The sensors run by the CTBTO are a hundreds times more sensitive than these latter detectors.
Additionally, the U.S. Environmental Protection Agency (EPA) runs a nation-wide, monitoring network of 124 sensors — 20 of which were not working when the Tohoku quake hit.
| EPA Fact Sheets on Commonly Encountered Radionuclides | ||||
|---|---|---|---|---|
| Radiation Type | ||||
| Name | Atomic Number | Alpha | Beta | Gamma |
| americium-241 | 95 |  |
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| cesium-137 | 55 | |
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| cobalt-60 | 27 | |
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| iodine-129 &-131 | 53 | |
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| plutonium | 94 | |
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| radium | 88 | |
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| radon | 86 | |
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| strontium-90 | 38 | |
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| technetium-99 | 43 | |
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| tritium * | 1 | |
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| thorium | 90 | |
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| uranium | 92 | |
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| * tritium is a specific isotope, H-3. | ||||
Currently, all functional monitoring station (in the U.S.) report beta and gamma gross count rate measures “thousands of times below any conservative level of concern.” (RadNet)
Further measurements are being conducted by specialized U.S. aircraft (see image below for an example) and mobile sensors, much of which have been deployed to Japan.
Despite this abundance of radiation sensing equipment, and the free flow of detector data to the Japanese government, said government (and TEPCO, the utility company that operates the reactors) have been slow in sharing data with the public.
Most state Departments of Health and the U.S. Environmental Protection Agency (EPA) post daily radiation measurements. However, this data can be confusing or difficult to interpret as none of the agencies translates these measurements into clear, radiation exposure risks to people. This is due to the fact that calculating the risk to people from exposure to any given radionuclide involves factoring in many variables, such as body weight, location, duration of exposure, means [inhaling/eating] of exposure, etc., making any meaningful assessment quite difficult.
If you’d like to see where your state stands in terms of radiation exposure (as measured by this EPA network), check out the EPA’s RadNet Air Monitoring site.
*PNNL is not an official member of the UN-based CTBTO network
Some source material for this post came from the March 25, 2011, Seattle Times article The Small World of Big Nuclear Worries, by Sandy Doughton.
Top images (instrumentation): Washington State DOH
