How Scientists Track Global Radiation Spread


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.

Radiation monitoring equipment in Tumwater, Washington.
(close-up of lead image) Radiation monitoring equipment in Tumwater, Washington.

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 Americium is  primarily an alpha particle emitter. It also emits some gamma rays. Americium  primarily emits alpha particles, but also emits some gamma rays.
cesium-137 55 Cesium-137 is  a beta particle emitter. Cesium-137 is  a gamma emitter.
cobalt-60 27 Cobalt-60 is a  beta particle emitter. Cobalt-60 is a  gamma emitter.
iodine-129 &-131 53 Iodine-129  and -131 are beta particle emitters Iodine-129  and -131 are gamma ray emitters
plutonium 94 Most  plutonium isotopes are alpha particle emitters; some emit other forms of  radiation. Most  plutonium isotopes are alpha particle emitters; some emit other forms of  radiation. Most  plutonium isotopes are alpha particle emitters; some emit other forms of  radiation.
radium 88 Radium  isotopes are alpha particle emitters. Radium  isotopes are also gamma ray emitters.
radon 86 The isotopes  of radon are alpha particle emitters.
strontium-90 38 Strontium-90  is a beta particle emitter.
technetium-99 43 Technitium-99  is a beta particle emitter. Technitium-99m  is a gamma emitter.
tritium * 1 Tritium is a  beta particle emitter.
thorium 90 Thorium emits  alpha particles with gamma rays Thorium emits  alpha particles with gamma rays
uranium 92 Uranium is an  alpha particle emitter. Uranium is a  gamma ray emitter.
* 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.

Proteus in flight during the Fall 2002 Intensive Operational Period for the Atmospheric Radiation Measurement Unmanned Aerospace Vehicle Program. Aircraft such as this can be used to monitor radiation emissions from nuclear accidents.

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

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