CHAPTER THREE A critical feature of the Enewetak Radiological Support Project was timeliness. Early in the planning stages it became clear that traditional techniques and methods of radiological survey would simply not be applicable in this remote location and under these operational circumstances. DNA expected to have as many as a thousand people conducting and supporting the cleanup, and the mostcritical elements of their task would require daily and detailed technical guidance from the ERSP. Thus, we could not afford the time which would normally be required to acquire, package, ship (to home laboratories), analyze, interpret and report upon the many thousands of soil samples necessary to characterize the atoll’s islands. The new approach to soil characterization, evolved during 1976, was to make the measurements on the islands, in-situ, supported by only limited soil sampling to assist with interpretation. Data were thus made available almost in real time, and the data flow and resulting technical guidance were consistently able to keep pace with the operational progress. This chapter describes the in-situ system and its use. As a new application of technology under remote and difficult circumstances, its success is a credit to those responsible for its design, construction and operation. Project Manager’s Note ON-SITE RADIOLOGICAL MEASUREMENTS W. John Tipton and Ray J. Jaffe EG&G - Las Vegas, Nevada 3.1 AERIAL SURVEYS Two aerial radiation surveys were conducted at Enewetak Atoll prior to actual initiation of cleanup activities. These surveys were performed by the U.S. Department of Energy's Remote Sensing Laboratory, operated for the DOE (and earlier for the AEC and ERDA) by the Energy Measurements Group of EG&G. The first survey was conducted in the fall of 1972 as part of a comprehensive effort to assess the radiological condition of the atoll prior to developing a cieanup plan. Two large arrays of sodium iodide (Nal) scintillation detectors were used, each containing twenty 12.7-em diameter by 5.1-em thick thallium activated sodium iodide (Nal (TY) seintillation detectors, mounted inside a CH-53 helicopter. Spectral data were acquired continuously in a 300 channel pulse~height analyzer and stored on magnetic tape in 3-second data blocks. Position information was obtained with an inertial navigation system and recorded each second on magnetic tape. All islands within the atoll were surveyed at an altitude of 30 meters, with 45-meter line spacing. The radiation data obtained from the aerial survey were processed to provide total terrestrial gamma ray exposure rate values extrapolated to microroentgen per hour (uR/h) at the | meter level, as well as the individual exposure rate contributions due conducted over Yvonne. These island photographs, formed an cleanup plan. Complete results to 137Cs5 and 88Co. A special low energy survey for 241 am was also results, presented in the form of radiation contours superimposed on integral part of the data base used for developing the Enewetak for the entire reconnaissance survey are given in NVO-140,. Although the 1972 aerial survey helped to provide a comprehensive overview of the radiological conditions at Enewetak, only limited data were obtained for 241Am, which was to become the indicator isotope for the cleanup project. July For this reason, a second aerial survey was conducted in 1977. This survey concentrated on measuring the 60 kiloelectron volt (keV) gamma ray from Am and only covered the northern islands from Alice down through Yvonne. The 1977 survey employed the same sodium iodide detector array as utilized in the 1972 survey. However, the 83