The accompanying map shows the results of an airborne radioactivity survey along the Gulf of Mexico beach between Sanibel Island and Caladesi Island in Florida. This survey was made May 4, 1953, as part of a cooperative program with the U.S. Atomic Energy Commission. The survey was made with scintillation detection equipment mounted in a Douglas DC-3 aircraft and consisted of one flight line, at a 500-foot altitude , parallel to the beach. The vertical projection of the flight line coincided approximately with the landward limit of the modern beach. The width of the zone on the ground from which anomalous radiation is measured at the nominal 500 foot flight altitude varies with the areal extent and intensity of the radioactivity the width of the zone may be as much as 1400 feet. The accompanying map and index map show the approximate locations of the areas of greater-than-average radioactivity and the location of the traverse flown. The abnormal radioactivity is apparently caused by radioactive minerals associated with "black sand" deposits which occur locally along the beach in the region. The present technique of airborne radioactivity measurement does not permit distinguishing between activity due to thorium and that due to uranium. An anomaly, therefore, may represent radioactivity due entirely to one or to a combination of these elements. It is not possible to determine the extent or radioactive content of the materials responsible for the abnormal radioactivity. The information given in the accompanying map showing the localities of greater-than-average radioactivity therefore, suggests area in which uranium or thorium deposits are more likely to occur.
