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History
The United States conducted 210 aboveground nuclear weapons tests in the lower 48 states and the Pacific Ocean between July 1945 and November 1962. The Nevada Test Site (NTS), a 1350 square-mile area about 65 miles northwest of Las Vegas, accounted for 100 tests. The first aboveground test took place at NTS on January 27, 1951, and the last was July 17, 1962.
A total of 828 nuclear weapons tests were conducted underground and continued until September 23, 1992. President George Bush declared a nine-month moratorium on October 2, 1992, banning all tests until July 1, 1993. President Bill Clinton then extended the testing moratorium until October 1994. On October 13, 1999, the Senate failed to ratify the Comprehensive Test Ban Treaty. No nuclear weapons tests have been conducted by the United States since the beginning of the moratorium.
Radioactive Fallout—General Information
A number of factors, such as weather conditions and the strength of the weapon, affected the distribution of radioactive fallout from nuclear weapons tests. “The earlier, low-yield fission weapons deposited much of their debris in the general area around the test sites, whereas the high-yield thermonuclear weapons tested later produced radioactive fallout on a global scale,” according to Appendix B of the National Council on Radiation Protection and Measurements Report 94. “For the tests in Nevada, the yield was only about 0.5 percent of the global total. However, while much of the exposure has been quite uniformly distributed on a hemispheric basis, there is still some interest in the doses delivered locally from testing in Nevada.”
Radioactive Fallout—Global and National Effects
The United Nation Scientific Committee on the Effects of Atomic Radiation periodically publishes a report to the General Assembly on the sources, effects, and risks of ionizing radiation. The 1988 report (UNSCEAR 88) summarized conclusions reached in previous UNSCEAR reports regarding radiation doses received from nuclear explosions. “In the first four UNSCEAR Reports (1958-1966), the Committee described in detail the meteorological processes that deplete the stratospheric inventory of radioactive debris. For man, the highest exposure was found to be due to long-lived radioactive material that causes radiation exposures over many years. The dominant radionuclides were strontium-90 (half-life:28 years), cesium-137 (30 years) and carbon-14 (5700 years). Some gamma-emitting radionuclides from tropospheric fallout, e.g., zirconium-95 and ruthenium-106, could also contribute significantly through exposure from the ground deposition.”
People in some areas of the United States received external and internal radiation exposure from short-lived radioactive materials for a few days or weeks following the weapons tests until the radioactive materials had decayed to levels indistinguishable from normal background radiation. One short-lived radioactive material of interest for internal exposure was iodine-131. A recently published National Institute of Health (NIH) document described the deposition of radioactive iodine across the United States from nuclear weapons testing.
Radioactive Fallout—Local Effects (SW Utah)
According to a United States Department of Energy Nevada Operations Office (DOE-NV) publication “A Perspective on Atmospheric Nuclear Tests in Nevada,” areas in Southwestern Utah were in the fallout patterns of nuclear weapons tests from one to six times. (St. George: 6, Cedar City: 5, Parowan and Paragonah: 4, and Kanab: 1)
“The majority of the exposure would have occurred during the first week following deposition (for each new deposition), and the rate of exposure would have decreased from then on. Radionuclides with a long half-life are still present in the environment but at a relatively low activity level,” according to a DOE-NV publication entitled “A Perspective on Atmospheric Nuclear Tests in Nevada.”
Environmental Monitoring Programs
Various programs existed, both on and off the NTS, to monitor the release of radioactive material from nuclear testing. Prior to 1954, the Los Alamos Scientific Laboratory and the U.S. Army maintained an offsite surveillance program. The U.S. Public Health Service monitored offsite releases from 1954 to 1970. Early monitoring involved collecting fallout materials on paper covered with a sticky film. Later monitoring involved measuring ambient radiation levels, radioactive noble gases (xenon and krypton), and tritium (radioactive hydrogen). Monitoring also involved collecting samples of hay, milk, soil, plants, and wildlife.
After December 1970, the newly created U.S. Environmental Protection Agency (EPA) assumed the responsibility of monitoring by combining various Federal monitoring programs, including the Offsite Radiological Environmental Monitoring Program (OREMP). On July 1, 1973, the EPA implemented a new monitoring system known as the Environmental Radiation Ambient Monitoring System (ERAMS). ERAMS incorporated portions of previous monitoring networks, which included the Radiation Alert Network, Tritium Surveillance System, Interstate Carrier Drinking Water, and the Pasteurized Milk Network. Scaled-back versions of OREMP and ERAMS are still active.
A community-based monitoring system, the Community Environmental Monitoring Program (CEMP), was also established. CEMP is administered by the Desert Research Institute (DRI) which is part of the Nevada System of Higher Education. The network stations collect a variety of radiological data in addition to other environmental/meteorological data and are staffed by local citizens (mostly high school science teachers). The CEMP has four stations in Utah (Delta, Milford, Cedar City, and St. George). The local citizens are responsible for collecting air filters and sending them to a commercial laboratory for analysis.
Additional Information
- Health Physics Society: Ask the Experts Q & A
Specialists in radiation safety.