Watertown as a radiation field laboratory
Shot DIABLO was fired on top of a 500-foot steel tower in Area 2 on 15 July 1957. It had a yield of 17 kilotons (the bomb dropped on Hiroshima, Japan, during World War II had a 13KT yield). Radiation safety (RAD-SAFE) monitors instrumented buildings and vehicles at Watertown to measure radiation-shielding capabilities of materials commonly found in an average U.S. town.
Ten days later, 17-kiloton shot DIABLO vaporized its 500-foot tower on the northwest corner of Yucca Flat. The fiery mushroom cloud sucked up dust and debris and, predictably, headed northeast across the hills. AEC monitors at Watertown documented radiation levels as measured by equipment placed in various buildings, vehicles, and open areas. The airbase included structures made from wood, sheet metal, plaster and other materials commonly found in an average American small town. Therefore, the data provided information on the characteristics of these materials to protect inhabitants against radioactive fallout. The information was logged in tables of "shielding data" for later study. Watertown shielding data from several shots, including DIABLO, is now available to any interested person at the DOE Public Reading Facility in Las Vegas, Nevada. The data tables for DIABLO list readings taken at the Groom Mine main residence, a wood-frame house where radiation levels reached a maximum of 80 milliroentgens per hour (mR/hr). By comparison, normal background levels are between 0.02mR/hr and 0.04mR/hr. Readings were taken at Watertown in several rooms inside wood-frame dormitory Building 103. Levels varied from 12mR/hr to 30mR/hr inside the building. Readings inside Trailer 10, with four-inch-thick aluminum and wood walls, went off- scale three hours after DIABLO detonated. Within an hour, levels dropped to 65mR/hr, and then 24mR/hr 90 minutes later.
A warehouse west of the Watertown trailers experienced a maximum of 75mR/hr inside, while levels outside the building reached 110mR/hr. The Base Theater received 90mR/hr for a few minutes as the cloud passed. Levels inside the cab of the Control Tower reached 37mR/hr, while outside levels were up to 60mR/hr. Additional readings were taken in several types of office and storage buildings, and even on the Volleyball court.
Measurements were also taken inside parked vehicles positioned on Groom Lake Road. Radiation monitoring equipment was placed inside trucks, some with closed windows and some open. One truck (with windows open) was located 9.5 miles west of Watertown, along Groom Lake Road. This turned out to be a real "hot spot." The interior of the metal cab received 950mR/hr, while outside registered 1,420mR/hr (or 1.42R). Another truck, two miles west of Watertown only received 0.3mR/hr inside the cab and 0.5mR/hr outside.