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Operation UPSHOT-KNOTHOLE. Project 8.2. Measurement of Thermal Radiation with a Vacuum Microphone.

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Technical Report

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Air Force Cambridge Research Center Cambridge

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The object of this project was to obtain a quantitative proof of the feasibility of the vacuum microphone for the measurement of theintensity of thermal radiation from nuclear detonations. Ten sets of measurements were made on the thermal radiation from as many shots.Data were recorded on magnetic tape and later filmed from an oscilloscope. Sensing elements were placed near ground zero at distancesvarying from 5309 ft to 10,568 ft. Additional units were located at the manned stations at distances varying from 6.49 to 13.0 miles. Time intensity curves for all shots have been integrated to obtain total thermal energy. Times to first minima and second maxima are given for all 10 detonations. Curves of Thermal Energy KT vs Total Weapon Yield KT, Thermal Energy per KT vs Slant Range, and Times of First Minima and Second Maxima vs Total Weapon Yield, are plotted. Sufficient engineering data have been obtained to demonstrate that the vacuum microphone is a suitable device for the measurement of intense thermal radiation with good time resolution. Microphones have been developed with high sensitivity and low noise factors. The values for the thermal yields are in substantial agreement with those obtained by NRL and NREL. The values obtained with this equipment for Shots 4 and 10 are closer to those reported by NRDL, and are slightly closer to the results of NRL for Shot 9. However, in this case there is only a maximum deviation of 5 per cent in the data submitted by ell three agencies.

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