} although not of comparable precision and accuracy to the primary data, were useful in determining the range and variation of the radiation field. G.M. Survey Meters - A number of G-M type Radiac Meters (IM-85/PDR-27F), supplied by NRDL, were used to obtain a wide coverage of total exposure rate data. These particular instruments were chosen for their ruggedness and dependability under severe environmental conditions. Although these survey meters were calibrated in the laboratory it was found that the calibration factor was unsuited to environmental radiation half-space geometry. The instruments exhibited a considerable energy and angular response when exposed to different energy sources in the laboratory. as well as a slight f-ray response even with the 6-ray shield closed. For these reasons it was felt that the laboratory calibration shouid be discarded in favor of a "field calibration" against the ionization chamber and spectrometer. Because of the lack cf sensitivity of G-M tubes to gamma radiation at the relatively low levels usuaily encountered, an individual reading taken with one of these instruments was imprecise. However, the mass of data taken when corrected using the "field calibration” satisfied the primary purpose of the instrument which was te delineate the range of exposure rates over a giver island and the variation from island to island. Survey meter readings were made on paths which were cut through the thick brush cn many of the islands (particularly on Bikini Island} along lines which ran lengthwise along the island, across the island or around the perimeter, 50 to 100 ft. inland. The thickness of the brush dictated where transects could be iocated and the transects frequently deviated substantially from straight lines. The meters were generally monitored constantly along the transects with readings recorded about every 50 ft. festimated}. Readings were taken at about the three foot Level, although as expected for y radiation, there was no significant variation with i ~J height. Readings were also made next te any unusual artifacts, scrap metal, bunkers, or building remains.