Chopter 3 RESULTS 3.1 INSTRUMENTATION PERFORMANCE The bulk of the radiation-detection equipment performed satisfactorily throughout the operation. The limit of detectability was determined by the background dose rate on, or close to, the detector. Because the source of radiation to be measured, namely the surface of the sea, was located considerable distance from the radiation detectors, contamination on or clase to the de- tector units would contribute a relatively large portion of the total reading. The aernal-survey dose-rate measurements were continuously recorded and stored on a strip~ chart recorder. The strip charts were correlated with the navigational logs to develop preliminary isodose plots. The results of the surveys are presented in this compiled form. The altitude ausorption measurements are presented as gamma dose rate versus altitude and have been fitted to an appropriate, derived curve. 3.1.1 Aerial Surveys. The records of 37 pre- and post-flight calibrations of the Top Hat detectors have been summarized in Figure 3.1. minus 1 percent of the dcsired curve. Thirty-two calibrations were within plus or This is within the reading accuracy of the recorder. A 1-percent instrument stability corresponds to a 10-percent radiation variation because of the logarithmic character of the scale. All calibrations were within a maximum limit of + 25 percent of the desired response. As mentioncd previously, the automatic telemetcring system failed to provide reliable trans~ mission of the aircraft data to the control center on the USS Estes, AGC-12. Voice relay of the recorder readings over the navigational net, Channel C, was substituted. The ship’s radio receivers did not provide clear, long-range communication with aircraft operating at an altitude af 300 feet. A radio receiver, U.S. Army R-390, was obtained from Task Unit 3 and tuned to the aircraft frequency, Channel C. he R-390 had a lower noise level, and the aircraft transmissions could be clearly detected at a greater distance. When an aircraft exceeded the reliablecommunication range, messages were relayed through a second aircraft. 3.1.2 Altitude Absorption. The automatic gamma monitors mounted on the YAG-39 and YAG-40 were calibrated for each shot participation prior to departure from Site Elmer, Exami- nation of the calibration records shows close conformity to the desired radiation response, A plastic bag was used to protect each monitor. However, the bag became contaminated during fallout, and the readings of sea activity were completely masked. The readings could not be used to provide a surface measurementfor aircraft-altitude calibration. The scintaineter survey meter was calibrated just prior to each helicopter mission. Long- term stability was not required for this application. When used in a helicopter, the gamma spectrometer required alternating current power which was Supplied by inverters fed from the 28-volt supply in the helicopter. the vibrator-type inverters failed. prior to Shot Mohawk. During Shot Seminole, Rotary converters were obtained, anda dry run scheduled The energy response was checked against sources containing known radioisutopes, and the performance was satisfactory. The mission was flown on Mohawk D + 2. On arvival at the station, the recorder failed because of the heavy vibration encountered during the hovering of the helicopter. Visual observation of the meter was used to obtain general energy distributions at 500 and 800 feet. The pilot was unwilling to risk hovering at lower altitudes. 24