: Chapter / INTROOUCTION 1.1 OBJECTIVES The objective was to measure the neutron spectrum and total prompt gamma ray flux produced by the detonation of a nuclear device of low yield _Atanaltitude of about 90,000 feet. This information was to be obtained by suitable detectors in the vicinity of the nuclear device and telemetered to the ground to be recorded and subsequently analyzed. 1.2 BACKGROUND During Operation Teapot, neutron flux from a device detonated at 36,600 feet above mean sea level (Shot 10) was measured by means of threshold fission and activation de- tectora in canisters dropped from the delivery aircraft. Gamma rays were measured with dosimeter films, DT/60/PD service dosimeters, silver phosphate giass and chemtcal dosimeters. Several fission-threshold detectors with thresholds at 200 ev, 1,000 ev, 700 kev, and 1,500 kev were used. The differences in flux given by these detectors were plotted as a histogram (Reference 1). A rough picture of the spectrum was given. Thresh- old detectors do not permit a detailed analysis of the spectrums for reasons diacussed in Reference 1. Time-of-~flight methods can give good energy-spectrum measurements if the geometry is good (neutrons scattered into the detector are excluded or negligible) and if the time duration of neutron production is short, compared to the mean time of flight. At the altitude planned for the very-high~altitude burst (Shot Yucca), the air density is approximately 1 percent of the air density at sea level. For this small denatty and for small ranges, the time-of-flight method for measurements of neutron-energy spectra be- comes feasible. The neutron-threshold data from Shot 10 of Operation Teapot was used to calculate the conditions for the measurement. Originally, it was planned to use a “real time” telemeter link, i.e., the telemeter would transmit the signal instantaneously. It was noted, however, that the blast data telemeters in the near canisters during Shot 10 of Operation Teapot were inoperative for a period in the order of seconds, caused by absorption of the telemetering signal by the intense gamma-ray ionization produced by the nuclear device. The theory of this attenuation was inadequate for the calculation of the attenuation in the very-high-altitude case. It was not possible to choose either operating frequency or transmitter power without detailed knowledge of the attenuation. Therefore, measurements of attenuation were made in the X band range during Operation Redwing (Reference 2). Although the measurements were successful, they were made at only one frequency and one range. On the basis of the Redwing data, a real-time link might be successful. To enlarge the data and to field test telemeter technique, fur-