Late last week, the U.S. Environmental Protection Agency confirmed that no radiation levels of concern entered the continental U.S. following the containment breach at nuclear reactors in Japan following a magnitude-8.9 earthquake and subsequent tsunami.
The confirmation was made possible with the use of two nationally-recognized devices developed at Pacific Northwest National Laboratory, which detect nuclear detonations by analyzing the atmosphere for traces of radioactive material. These systems, which work in tandem, are located around the globe and are used to monitor international compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) by detecting nuclear explosions. The devices are called the Automated Radioxenon Sampler Analyzer (ARSA) and the Radionuclide Aerosol Sampler/Analyzer (RASA).
Both detectors types are deployed worldwide, and were the first to detect radioactive isotope xenon-133 entering the continental United States on Wednesday, March 16, 2011. The origin of the materials was consistent with a release from the Fukushima nuclear reactors in northern Japan a few days earlier. The levels were extremely low an posed no health hazard, since the dose rate detected was less than one-millionth of the amount a person normally receives in one day from background radiation produced by sources like the sun.
In 1998, DME Corp. and Pacific Northwest National Laboratory were recognized by R&D Magazine for the development of RASA, which is often used in concert with ARSA.
What is ARSA and RASA?
Since the first nuclear test in the years following World War II, the world has been living under the threat of nuclear attacks. The Comprehensive Nuclear-Test-Ban Treaty (CTBT), which was adopted in 1996 by the United Nations' General Assembly, signed by 150 nations and ratified by more than 60, requires a network of 80 radionuclide monitoring stations covering the globe. Many monitors are in place to ensure the success of the treaty.
Automated Radioxenon Sampler-Analyzer beta-coincidence spectrometer is an integral part of the system. The system analyzes air samples for radioactive xenon. It detects the evidence of the most difficult to detect underground nuclear explosions as well as any evidence of atmospheric radiation resulting from other activity with a sensitivity of 10 to 100 times greater than other systems being used.
This subject is just as crucial today as it was during the heyday of U.S. testing in the 1950s. The provocative nuclear testing undertaken by India and Pakistan in 1998 showed that testing can escalate international tensions and could possibly result in a disastrous nuclear war in which many millions of innocents die.
The Radionuclide Aerosol Sampler/Analyzer (RASA) and Automated Radioxenon Sampler Analyzer (ARSA) nuclear explosion identification devices are fast becoming part of the monitoring arsenal to verify international compliance with the CTBT. The RASA and ARSA represent a quantum leap beyond previous monitoring devices, with greater sensitivity, full automation, near-real time reporting, and novel nuclear radiation detectors. Radionuclide detection is unique-it is the only method to provide absolute proof of a nuclear explosion. RASA and ARSA can definitely prove it was a nuclear explosion, while other technologies cannot.
The technologies moved from concept to commercialization in only six years. Because they are reliable, can collect large sample volumes without requiring human labor, and inexpensive, RASA and ARSA have been chosen by the United States and a growing number of other countries to be part of the monitoring regime to verify international compliance with the CTBT.
The RASA detects fission products in the form of particulate debris from atmospheric nuclear explosions. It filters a huge volume of air each day to check for evidence of fission products from a nuclear explosion that attach to dust particles. The automated system draws air through a series of filters, which remove practically all of the atmospheric particles. The filters are sealed, bar coded, and then passed to a radiation detection system. Radiation from weapons debris is then registered and translated to prove a violation of the treaty. Researchers at PNNL have created the most sensitive automated system—more than 100 times as sensitive as the best previous commercial technology.
The ARSA analyzes air samples for radioactive xenon, or radioxenon, that seeps from underground nuclear explosions, the most common testing method today but the most difficult to detect. ARSA can detect xenon with a sensitivity nearly 100 times greater than other systems being used, and is the only automatic system available. ARSA collects air samples, and processes them to trap the radioactive xenon on cold charcoal. The system purifies the radioactive xenon, and transfers it to a nuclear counting system. The different isotopes of xenon are automatically measured, and the results are automatically passed to a data center by communication link. Both the ARSA and RASA can be completely monitored, controlled, and programmed remotely to lower operating costs.
EPA/DOE statement: Radiation monitors confirm that no radiation levels of concern have reached the United States
The United States Government has an extensive network of radiation monitors around the country and no radiation levels of concern have been detected. The U.S. Environmental Protection Agency RadNet system is designed to protect the public by notifying scientists, in near real time, of elevated levels of radiation so they can determine whether protective action is required. The EPA’s system has not detected any radiation levels of concern.
In addition to EPA’s RadNet system, the U.S. Department of Energy has radiation monitoring equipment at research facilities around the country, which have also not detected any radiation levels of concern.
As part of the Comprehensive Nuclear Test Ban Treaty Organization’s International Monitoring System (IMS), the Department of Energy 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.
Today, 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, these 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 the Department of Energy’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.
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.
As part of the federal government’s continuing effort to make our activities and science transparent and available to the public, the Environmental Protection Agency will continue to keep all RadNet data available in the current online database.