eo _ DRAFT The instruments were calibrated with a 137Cs point source on the primary calibration range of the National Environmental Research Center, Las Vegas, Nevada. While the response of this instrument is energy-dependent, our experience at Enewetak showed that this was not a serious limitation because of the dominance of 13’Cs in the radiation background on the Atoll. We also utilized the Reuter-Stokes high pressure ionization chamber. The current produced by the radiation induced ionization within the chamber is measured by a sensitive electrometer with digital readout. The instrument exhibits a flat energy response over all gamma-ray energies of interest to this survey. It is capable of measuring exposure. rates from about 1 upR/hr to 200 upR/hr with an accuracy of about 5%. Thus, the results derived from this instrument were chosen as a reference to which measurements obtained by other techniques were compared. Measurements of the exposure rate at 1 m above the ground were made with the Nal scintillator at approximately 2500 locations on a 30-m rectangular grid on Bikini Island and at about 120 locations on a 120-m grid on Eneu Island. The jonization chamber was primarily used for measurements within the central section of Bikini Island with additional measurements made at selected areas. Thus, from this program a very comprehensive picture of the gamma-ray exposure rates is available for both islands. Thermoluminescent dosimeters (TLD's) were also employed to supply a third technique for evaluating the external dose. A complete report on the external gamma measurements and resulting dose assessment has been published (2). - 900938 18