An aerial radiological survey of the Nevada Test Site

A team from the Remote Sensing Laboratory conducted an aerial radiological survey of the US Department of Energy's Nevada Test Site including three neighboring areas during August and September 1994. The survey team measured the terrestrial gamma radiation at the Nevada Test Site to determine the levels of natural and man-made radiation. This survey included the areas covered by previous surveys conducted from 1962 through 1993. The results of the aerial survey showed a terrestrial background exposure rate that varied from less than 6 microroentgens per hour (mR/h) to 50 mR/h plus a cosmic-ray contribution that varied from 4.5 mR/h at an elevation of 900 meters (3,000 feet) to 8.5 mR/h at 2,400 meters (8,000 feet). In addition to the principal gamma-emitting, naturally occurring isotopes (potassium-40, thallium-208, bismuth-214, and actinium-228), the man-made radioactive isotopes found in this survey were cobalt-60, cesium-137, europium-152, protactinium-234m an indicator of depleted uranium, and americium-241, which are due to human actions in the survey area. Individual, site-wide plots of gross terrestrial exposure rate, man-made exposure rate, and americium-241 activity (approximating the distribution of all transuranic material) are presented. In addition, expanded plots of individual areas exhibiting these man-made contaminations are given. A comparison is made between the data from this survey and previous aerial radiological surveys of the Nevada Test Site. Some previous ground-based measurements are discussed and related to the aerial data. In regions away from man-made activity, the exposure rates inferred from the gamma-ray measurements collected during this survey agreed very well with the exposure rates inferred from previous aerial surveys