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On this Page:
- Why is RadNet needed?
- Why does EPA test air, precipitation, drinking water and milk for radionuclides?
- Does RadNet cover the whole U.S.? How does EPA decide where to set up air monitors and take samples?
Why is RadNet needed?
RadNet is one of many radiation monitoring systems in the U.S. For example, there are highly sensitive detectors set up to monitor compliance with the Comprehensive Nuclear Test Ban Treaty and many states and all nuclear power plants have monitoring systems.
However, RadNet is the only nationwide system that continuously monitors ambient environmental radiation levels and those resulting from major nuclear accidents, such as the Fukushima nuclear reactor incident in Japan. RadNet data are used to inform the public, providing assurance if contamination levels are very low or helping to make science-based decisions about taking protective actions if contamination levels are high enough to warrant them.
Why does EPA test air, precipitation, drinking water, and milk for radionuclides?
Contamination from nuclear incidents typically travels through the air in the form of particulates, although some contamination may be gaseous or become waterborne. By monitoring for airborne particulates, EPA's health physicists can estimate inhalation doses to humans. Measuring precipitation provides a good way to determine the amount of contamination which is stripped from the air by rain or snow and deposited on the ground. EPA monitors drinking water and milk to help public officials determine if food and water supplies are safe for consumption. Actual food supply monitoring is provided by the U.S. Food and Drug Administration. EPA is also considering expanding the program to better protect you from contamination due to nuclear events. Here's more about the air, drinking water, milk and precipitation monitoring programs.
Does RadNet cover the whole U.S.? How does EPA decide where to set up air monitors and take samples?
RadNet air monitoring and sampling stations are widely distributed across the entire U.S. The system is designed to estimate ambient levels of radioactive pollutants in our environment, follow trends in environmental radioactivity levels, and measure widespread impacts from an incident that might occur anywhere in the U.S. or abroad. Monitoring and sampling sites were chosen to provide optimum population and geographical coverage throughout the United States and the most efficient use of Agency resources. They track background radiation in each geographical region, most individual states, and most major population centers during normal times and test for radioactive contaminants during emergencies. EPA has 40 additional monitors that can be deployed anywhere in the U.S. if needed.
- Where can I see RadNet monitoring data and sampling analysis/laboratory results?
- How does EPA use RadNet data?
- Why are there fluctuations in the data?
- Where can I find beta monitoring data?
- Why do I see higher levels of radiation at some monitor locations?
- How does EPA use gamma energy ranges?
- What are the energy ranges for the gamma charts?
Where can I see RadNet monitoring data and sampling analysis/laboratory results?
RadNet monitoring and laboratory results are available on-line:
- Envirofacts is a digital repository that includes RadNet data measured from air filters sent from each monitor, as well as current and historical radiation data on drinking water, milk, and precipitation.
- EPA's Central Data Exchange reports hourly environmental radiation data from fixed and deployable monitors. (Log-in is not required.)
- Environmental Radiation Data (ERD) is an electronic and print journal compiled and distributed periodically by EPA's National Analytical Radiation Environmental Laboratory (NAREL) in Montgomery, Alabama. It contains data from RadNet and its predecessor systems.
How does EPA use RadNet Data
RadNet data in the Envirofacts database are a rich source of radiation data. For example, this graph showing the long-term trends of tritium in precipitation (rain, snow, sleet) from monthly concentrations compiled between 1978-2001.
The graph shows the tritium concentration between 1978 and 1980 was about 350 (pCi/l), but spiked to about 680 pCi/l during the last above ground nuclear test, then declined to levels below what instruments can detect.
Beta particles and gamma rays, like all radiation, are natural and part of our environment. Tracking beta and gamma radiation, which are particles and rays that come from radioactive material, helps us to identify the type and amount of the radioactive material in the air. By looking at this data over time, scientists recognize what is "normal" or "background" radiation in that location. Any reading above normal will trigger an alert to EPA scientists to review the data. Scientists remove any data points from the database that are caused by instrument error or local radiofrequency interference.
During a radiological incident, RadNet data can be used to confirm that no excess radiation is present in an area or to help decision-makers decide whether appropriate actions need to be taken to protect the public. The monitoring data can also be used to confirm that the data generated by computer models are accurate. You can read more about RadNet data and its uses in the publication, Historical Uses of RadNet Data (PDF) (36 pp, 564K, About PDF)
Why are there fluctuations in the data?
Spikes in data can occur in a variety of situations, including fluctuations in naturally occurring radiation levels. These include release of radon from soil or water, concentration of natural radiation by rain, and changes in atmospheric (barometric) pressure.
Occasionally, you may see brief gaps in the data. Scientists remove any data points from the database that are caused by instrument error or radiofrequency interference. Larger gaps generally mean the RadNet monitor was temporarily taken offline for maintenance or repair.
Having a monitor offline is not cause for concern. Even if the closest monitor is not operating, the RadNet system as a whole continues to provide a national view of airborne radiation in the environment.
Where can I find beta monitoring data?
Reviewed and approved near-real-time beta air monitoring data are available by using the query tool to search the RadNet database in EPA's Central Data Exchange (CDX). Note that there may be large gaps in these data. Near real-time beta monitoring results frequently do not pass quality control criteria due to local radiofrequency interference. For this reason, near real-time beta monitoring graphs are not displayed on this site.
Beta activity levels from laboratory analysis of air filters are available in Envirofacts.
- RadNet Database in CDX
EPA provides environmental data in its Central Data Exchange. RadNet near-real-time air monitoring data are in the CDX RadNet database.
EPA provides RadNet sampling data in the RadNet data base of Envirofacts.
Why do I see higher levels of radiation at some monitor locations?
It is important to note that there are often large differences in normal background radiation across the nation. Background radiation levels depend on factors including altitude and the amount of naturally occurring radioactive elements in the soil. What is natural in one location may be different from what is natural in another.
How does EPA use gamma energy ranges?
Gamma radiation data from each fixed RadNet monitor are transmitted to EPA's National Analytical Radiation Environmental Laboratory (NAREL) hourly. The data are screened against pre-set values for each monitor to determine if there are abnormalities, particularly elevated radiation levels. In order to detect small increases in gamma radiation, EPA divides the gamma radiation measurement data into 10 different gamma energy regions. The first range is reserved for calibration with a known radioactive source. The ranges collectively cover the energy spectrum where the majority of gamma emitting nuclides are detected. EPA scientists analyze the complete gamma spectrum to detect the type and amount of gamma emitting radioactive material at that location.
When the RadNet computer system detects an abnormally elevated reading from a monitor in any of the gamma energy ranges, those data are flagged to be reviewed by EPA scientists. The review includes evaluating that spectrum from the monitor for both natural and man-made nuclides.
What are the energy ranges for the gamma charts?
The following table shows the energy ranges that correspond to the gamma charts on the near-real-time gamma gross count rate graphs.
|Energy Range Number||Gamma Energies [keV]||Line Color on Graphs|
|1||Reserved by software for instrument stabilization|
RadNet gamma detectors measure the radiation from all radionuclides collected on the filter that emit gamma radiation. Because of its design, electronics, and software, the gamma detector is able to distinguish between gamma photons of different energies and count rates, and produces a spectrum like the one shown below. For routine monitoring purposes, RadNet scientists divided each hourly spectrum into the gamma energy regions shown in the gross gamma count rate graphs. However, identifying the radionuclides present is not as simple as looking at peaks in a particular range. Interpreting the gamma count rate data from the RadNet fixed air monitors is a complex process. Because radionuclides often have primary and secondary peaks in different energy ranges, scientists don't look at any specific energy range to detect a specific nuclide. Users should not interpret the data in any specific energy range as indicating the presence or absence of a specific radionuclide.
Example of a Complete Gross Gamma Count Rate Spectrum Over Several Hours
The near-real-time gamma monitoring displays data in energy ranges. With the understanding that there can be variation in peak location, scientists know that certain radionuclide peaks typically show up in certain energy ranges. This helps us identify the type of radioactive material.
In the example above, the large peak in energy range 1 is called a "photo reference peak." It is produced by an americium-241 source interacting with a crystal inside the detector. Scientists know what the location of the reference should be and can correct the spectrum by shifting it until the reference peak is at the correct energy.
- Why does EPA monitor the air for radiation?
- How does EPA monitor the air for radiation?
- How do fixed (stationary) monitors work?
- What is a deployable monitor and how is it different from fixed monitors?
- Why isn't there a monitoring station in my hometown?
- How does the EPA measure radiation if there isn't an operating monitor in my area?
- When is air data available to the public?
- Why aren't the data graphs for my location up to date?
Why does EPA monitor the air for radiation?
EPA monitors the air for radiation in near real-time to understand levels of natural background radiation and to detect any elevation in levels of radiation so that scientists and officials can determine whether protective actions are required. The RadNet system has been used to detect and track radioactive material associated with foreign atmospheric nuclear incidents such as the Chernobyl disaster in Ukraine and the accident at the Fukushima nuclear power plant in Japan.
How does EPA monitor the air for radiation?
EPA's nationwide radiation monitoring system, RadNet, operates more than 100 radiation air monitors across the United States. The RadNet monitoring system runs 24 hours a day, 7 days a week, and transmits near real-time measurements of beta and gamma radiation to EPA's National Analytical Radiation Environmental Laboratory (NAREL). The near-real-time air monitoring data is continually reviewed by computer, and if the results show a significant increase in radiation levels, EPA laboratory staff is immediately alerted to investigate. The monitors have equipment to collect air samples for laboratory analysis and weather stations to record atmospheric conditions. The RadNet system also has 40 portable monitors that can be deployed to any location in the U.S.
How do stationary (fixed) monitors work?
RadNet fixed air monitors sample the air continuously at an approximate flow rate of 60 cubic meters per hour (Adults typically breathe at a rate of about 20 cubic meters per day.) The monitors collect any particles in the sample on a filter. Radiation detectors continuously measure the beta and gamma radioactivity from particles on the filter. Every hour, the stationary monitor sends an electronic report to EPA's National Analytical Radiation Environmental Laboratory (NAREL).
During sampling, EPA continuously monitors the amount of radioactivity collected on the air filter using two different types of radiation detectors. These detectors are positioned a small distance from and directly above the filter as shown in the photo on the right. The first detector, which is smaller and closest to the filter, measures beta particle radiation, and the second detector, connected directly above it, measures gamma radiation. Most naturally-occurring and man-made radionuclides emit either beta particles or gamma photons, and many emit both. The monitor sends a report to EPA that contains the total number of beta and gamma counts recorded by the detectors during the previous hour. By reviewing and comparing the beta and gamma count rates, EPA is able to determine whether fluctuations in these count rates are caused by normal background variations caused by naturally occurring radionuclides or to additional activity from man-made radioactive sources.
What is a deployable monitor and how is it different from stationary monitors?
A deployable monitor is portable and can be set up in any location as needed. During the Fukushima accident in Japan, EPA set up deployable monitors in Hawaii, Alaska and U.S. Pacific territories to expand the reach of RadNet monitoring. RadNet deployable monitors send both weather data and average gamma exposure rates to EPA's National Analytical Radiation Environmental Laboratory (NAREL). The deployable monitors do not measure beta radiation and have slightly different air sampling equipment.
Why isn't there a monitoring station in my hometown?
The RadNet sampling stations were selected to provide optimum population and geographical coverage throughout the United States. These stations are widely dispersed throughout the nation, covering each geographical region, most individual states, and most major population centers.
How does the EPA measure radiation if there isn't an operating monitor in my area?
EPA placed more than 100 monitors across the country to have an abundance of monitors providing overlapping coverage. If a monitor in one area is being repaired, EPA's network will still be able to detect any fluctuation in background levels in the surrounding areas.
When is air data available to the public?
The near-real-time air monitoring data are continually reviewed by computer and are usually posted to EPA's Central Data Exchange website within 2 hours of arriving at the laboratory.
If the results show an abnormality in radiation levels, EPA laboratory staff is alerted immediately and reviews the data to ensure accuracy before posting.
EPA scientists conduct a detailed analysis on RadNet air filters and cartridges. Data are posted in EPA's Envirofacts database.
Why aren't the results for my location up to date?
EPA's RadNet monitors are highly sophisticated technical devices which occasionally require maintenance and repair. In addition, some monitors are taken off-line because of severe radiofrequency interference in the vicinity of the monitor.
Air Filter, Precipitation, Drinking Water and Milk Sampling
- Why does EPA test air filters and cartridges for radionuclides?
- Where can I find the analytical results from air filter and cartridges?
- Why does EPA test precipitation for radionuclides?
- How does EPA sample precipitation?
- Are there EPA standards for radionuclides in rainwater?
- Where can I find the analytical results from precipitation samples?
- How does EPA sample drinking water for radionuclides?
- What if there is no RadNet water sampling in my town?
- What federal standards exist that address radiation in drinking water and milk?
- Where can I find the analytical results from drinking water samples?
- How does EPA sample milk?
- What federal standards exist that address radiation in drinking water and milk?
- Where can I find the analytical results from milk samples?
Air Filters and Cartridges, Precipitation, Drinking Water, and Milk
Air Filters and Air Cartridges
Why does EPA test air filters for radionuclides?
RadNet's laboratory analyses provide confirmation of the near-real-time monitoring results. By monitoring air and testing air filters on a regular basis, EPA is able to establish normal background levels of radioactivity and detect additional activity from man-made radioactive sources. All air filters go through an initial screening for beta radiation. Extremely low readings, below a conservative threshold, are posted to the Envirofacts webpage. Any filter that is found to have levels above the beta threshold are sent through a complete gamma analysis, where scientists can determine the exact type and amount of radioactive material present on the filter.
Where can I find the analytical results from air filter and cartridges?
You can obtain EPA's analytical results from air filters and cartridges on our Envirofacts site
Why does EPA test precipitation for radionuclides?
By monitoring precipitation on a regular basis, EPA is able to establish normal background levels of radioactivity and detect additional activity from man-made radioactive sources. Measuring precipitation provides a good way to determine the amount of contamination which is stripped from the air by rain or snow and deposited on the ground.
How does EPA sample precipitation?
More than 30 stations across the U.S. collect precipitation samples as rain, snow or sleet falls. Under routine circumstances, EPA scientists test the samples on a monthly basis. EPA performs gamma analysis on each sample. Routine analysis of precipitation for gamma emissions takes about a week from the time the lab receives the sample. The results are checked before being posted to assure that they meet quality assurance criteria.
Are there EPA standards for radionuclides in rainwater?
There are no standards for radionuclides in precipitation. The data we collect helps establish trends and serves as a reference during radiological incidents.
Where can I find the analytical results from precipitation samples?
You can obtain the analytical results of precipitation samples on our Envirofacts site.
How does EPA sample drinking water for radionuclides?
EPA's RadNet Drinking Water Program obtains quarterly drinking water samples from more than 50 sites across the country. EPA performs gamma analysis on each sample. Routine analysis of drinking water for gamma emissions takes about a week from the time the lab receives the sample. The results are checked before release to assure that they meet quality assurance criteria.
What if there is no RadNet water sampling in my town?
The RadNet radiation monitoring system provides a national network for tracking radiation levels across the country; it was not designed to monitor local water quality. Local water authorities test for compliance with EPA's drinking water standards.
What federal standards exist that address radiation in drinking water?
Under the Safe Drinking Water Act, EPA has set maximum contaminant levels (MCLs) to establish limits for certain substances in drinking water, including microorganisms, disinfectants, disinfection byproducts, inorganic chemicals, organic chemicals, and radionuclides. The MCLs for radionuclides were calculated based on long-term, chronic exposures over the course of a lifetime 70 years.
Where can I find the analytical results from drinking water samples?
You can obtain EPA's analytical results from drinking water samples on our Envirofacts database.
How does EPA sample milk?
Milk samples are collected and sent to EPA's National Analytical Radiation Environmental Laboratory (NAREL) by RadNet partners in over 30 s locations throughout the United States. These partners have a standing agreement with EPA to send milk samples on a quarterly basis. The milk that is sampled is sent to the lab before it is sent to stores, but generally after it has been pasteurized. The milk does not necessarily come from a specific farm.
The milk is analyzed for gamma emitters and selected sites are tested for strontium-90. A complete analysis can take up to three days, but preliminary results can be available within four hours.
- strontium-90 fact sheet
This fact sheet provides information about the discovery and properties of strontium-90.
What federal standards exist that address radiation in milk?
The Food and Drug Administration sets standards for radioactivity in milk. The Food and Drug Administration has set derived intervention levels (DILs) to assure that no one will reach a specific dose that would warrant protective actions as a result of a release of radionuclides. These levels also help the agency determine whether domestic food in interstate commerce or food offered for import into the United States presents a safety concern.
Where can I find the analytical results from milk samples?
You can obtain EPA's analytical results from milk samples on our Envirofacts site
Food and Imports
- Where can I find information about the radiation screening of imported products?
- How do I know that the food that I am eating is safe? Who monitors radioactivity in U.S. and imported foods?
Where can I find information about the radiation screening of imported products?
The U.S. Customs and Border Protection (CBP) is the federal agency in charge of screening imported products for harmful substances. You can find information about CBP screening of cargo for radiation at the Agency's Cargo Examinations page.
You can reach CBP staff by phone at 877-227-5511.
How do I know that the food that I am eating is safe? Who monitors radioactivity in U.S. and imported foods?
The U.S. Food and Drug Administration (FDA) is the federal agency in charge of monitoring food for radioactivity. FDA is part of the Department of Health and Human Services. Several agencies support FDA and cooperate closely. For example, the National Ocean and Atmospheric Administration (NOAA) works closely with FDA to monitor and sample the radiation levels of seafood in the ocean. You can find information about testing food for radiation by visiting FDA's Public Health Focus-Radiation Safety webpage. For information about U.S. food recalls and alerts, please visit, U.S. Food Safety: Recalls and Alerts.