Aerial gamma survey by helicopter to measure surficial contamination

A program was carried out to determine whether aerial γ surveys could adequately measure the activity of high specific activity γ emitters contaminating large land surface areas. The survey successfully measured the 137Cs activity and the total gross γ over areas from less than 1 to 20 km2. Also, 241Am was successfully measured over areas wherein the 137Cs was sufficiently low. Micro-curies per m2 were measured as low as 0.1 for 137Cs and 241Am. Other radionuclides such as 60Co were also detected. An aerial neutron survey was tried, though its efficiency limited detection to areas having more than 10 kg Pu per 4,000 m2. It was concluded that the aerial survey can analyze a complete area, thereby saving millions of dollars in statistical sampling and analytical programs. (U.S.)