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Operation UPSHOT-KNOTHOLE. Project 8.12b. Supplementary Pressure Measurements.

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Technical Report,01 Mar 1953,30 Jun 1953

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The purpose of this experiment was to check on the possibility that preshock pressures might be generated by sudden exposure of a surface to intense thermal irradiation, as from an air burst of an atomic weapon. Preshock pressures are defined as any change in the pressure datum, between weapon detonation time and main shock or precursor arrival time. Test panels 10 ft by 10 ft were installed at 1500 ft and 5000 ft ranges from intended ground zero for Shots 9 and 10 of Operation UPSHOT-KNOTHOLE. Three panels at each location were faced with materials selected for their thermal properties. The panels were inclined toward the expected detonation points so substantially more thermal influence would be obtained on the test surfaces than on the surrounding ground. The ranges selected were outside the region of extremely high overpressures and very early shock arrival times. The pressure datum was monitored at the center of each panel andalso at a ground level control station at each range by sensitive, fast responding, David Taylor Model Basin capacitance type pressure gages.No preshock activity was recorded on Shot 9. A sustained preshock record deflection, the equivalent of a positive overpressure of about 3 psi was obtained on Shot 10 from a gage at the center of a panel faced with soil from Frenchman Flat. This panel was at a ground range of 1493 ft and had been subjected to a total thermal flux of 60 calcm2 before the arrival of the main shock front. It appears that this might have been an actual pressure generated at the test panel but other factors related to the instrumentation preclude a positive conclusion on the basis of one isolated record.

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