at or above ground level, all of which involved releases of significant amounts of radioactive material into the atmosphere. Atmospheric testing was halted in 1958 after a testing moratorium was agreed upon with the Soviet Union. The Soviets broke the agreement in 1961, and both sides resumed testing. Two American test series followed: Operation Nougat, and then Operation Storax. The Partial Nuclear Test Ban Treaty went into effect in 1963, banning all above ground testing. Further tests were underground, which with the exception of a few test failures, did not release fallout. In the 1950s, people who lived in the vicinity of the NTS were encouraged to sit outside and watch the mushroom clouds that were created by nuclear bomb explosions. Many were given radiation badges to wear on their clothes, which were later collected by the Atomic Energy Commission to gather data about radiation levels. In a report by the National Cancer Institute, released in 1997, it was determined that the nearly ninety atmospheric tests at the Nevada Test Site (NTS) left high levels of radioactive iodine-131 (5.5 exabecquerels, Ebq) across a large area of the continental United States, especially in the years 1952, 1953, 1955, and 1957. The National Cancer Institute report estimates that doses received in these years are estimated to be large enough to produce 10,000 to 75,000 additional cases of thyroid cancer in the U.S. A 1999 review of the 1997 report considered that their estimates of collective doses were in "good agreement" and "should provide confidence that the NCI estimate is not grossly under or over the actual value." A 2006 report, published by the Scientific Research Society, estimates that about 22,000 additional radiation-related cancers and 2,000 additional deaths from radiation-related leukemia are expected to occur in the United States because of external and internal radiation from both NTS and global fallout. A 2010 report evaluating data on thyroid cancer incidence from 1973 to 2004 also supports a relationship between exposure from fallout and increased thyroid cancer incidence. The threat of downwind exposure to radioactivity remaining at the Nevada Test Site from nuclear weapons tests was still an issue as late as 2007. The Pentagon planned to test a 700-ton ammonium nitrate-and-fuel oil "bunker buster" weapon. The planned "Divine Strake" test would have raised a large mushroom cloud of contaminated dust that could have blown toward population centers such as Las Vegas, Boise, Salt