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 close to the detector units would contribute a relatively large portion of the total reading. The aerial-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 prelmi- nary isodose plots. The results of the surveys are presented in this compiled form. The altitude absorption 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. Thirty-two calibrations were within plus or minus 1 percent of the desired curve, This is within the reading accuracy of the recorder. A 1-percent instrument stability corresponds to a 10-percent radiation variation because of one logarithmic character of the scale. of the desired response. All calibrations were within a maximum limit of + 25 percent As mentioned previously, the automatic telemetering system failed to provide reliable trans- mission of the aircraft data to the control center on the USS Estes, AGC-12. recorder readings over the navigational net, Channel C, was Substituted. Voice relay of the The ship’s radio re- ceivers did not provide clear, long-range communication with aircraft operating at an altitude of 300 feet. A radio receiver, U.S. Army R-390, was obtained from Task Unit 3 and tuned to the aircraft frequency, Channel C. The R-390 had a lower noise level, and the aircraft trans-~ missions could be clearly detected at a greater distance. When an aircraft exceeded the reliable- communication 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. Examination 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 measurement for aircraft-altitude calibration. The scintameter 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. During Shot Seminole, the vibrator-type inverters failed. Rotary converters were obtained, anda dry run scheduled prior to Shot Mohawk. The energy response was checked against sources containing known radioisotopes, and the performance was satisfactory. The mission was flown on Mohawk D + 2. On arrival 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 €CO fect. The pilot was unwilling to risk hovering at loweraltitudes. 24 =: DOE ARCHIVES 2