For environmental monitoring, Project Grab Bag was an air sampling program conducted in the United States in the stratosphere of above-ground nuclear weapons testing in the Soviet Union. The objective of the Grab Bag program was to develop an unmanned high-altitude balloon-borne system that would collect air samples at an altitude of typically and return them to earth for analyses. The air samples were analyzed for the presence of specific isotopes of krypton and xenon, unambiguous markers of fission reactions. These short-lived isotopes are created in the fission process and carried high into the atmosphere by the fireball, where they will remain for some days. The air sampling system was developed by the Balloons and Meteorological Systems group at General Mills, Inc. in Minneapolis, Minnesota, using large balloons fabricated of thin polyethylene film. The initial test of the sampling system collected an important air sample over the United States on August 14, 1953, at an altitude of . This sample contained debris from a nuclear weapon test in the USSR, designated Joe-4, that was conducted two days earlier, on August 12, 1953, at Semipalatinsk in Kazakhstan. This was the first test of a thermonuclear weapon by the USSR and was initiated by a 40-kiloton uranium-235 bomb and produced a total yield of 400 kilotons. Background The first nuclear detonation was an above-ground test, “Trinity”, conducted in New Mexico on July 16, 1945. It represented an important accomplishment of the Manhattan Project that had been initiated at Los Alamos National Laboratory in 1943. In less than two months following this test, nuclear weapons assembled at Los Alamos were used in the Pacific War against Japan. Hiroshima was devastated on August 6, 1945 with a uranium-235 gun device with a fission product yield of about 15 kilotons. Three days later, on August 9, 1945, a plutonium-239 implosion device with a yield of about 22 kilotons was detonated over Nagasaki. These events significantly influenced the conclusion of World War II as the incredibly destructive power of these new weapons became apparent. The Manhattan Project brought together scientists from the US and Britain to collaborate on this nuclear weapons development program. Los Alamos was the epicenter of this activity, and, in spite of high-level security, it was realized in 1948 that security of the program had been breached. Klaus Fuchs, a British theoretical physicist intimately involved in some of the most sensitive aspects of