It was originally planned to conduct this evaluation on shot 9 with an operational smoke-screen setup using smoke generators, and/or smoke pots. Thermal flux data were to be obtained under the smoke screen at a@istances varying from 2,500 to 6,500 ft from ground zero of the nuclear device detonated 2,420 ft in the air. However, adverse wind conditions and possible interference with the overall test program under these conditions resulted in a last-minute cancellation of the smoke-screen test. With instruments recovered from shot 9, and new instruments fabricated in the interim, a preliminary study was rapidly planned for shot 10. The objective of this setup was to obtain partial data for a preliminary analysis of the Thermal Radiation Attenuating Clouds (TRAC) program and to obtain data applicable to future planning for a full-scale evaluation of an operational smoke screen. A single instrument station was located at a slant range of 2,261 ft from the detonation of a nuclear device approximately 500 ft in the air. The smoke screen for this test was created with 175 smoke pots surrounding the station in 200-ft and 300-ft diameter rings. gible ding Analysis of photographic records of the test has shown that the carbon-smoke screen, also set up on shot 10, intercepted the thermal radiation impinging upon the fog-oil smoke screen being tested by this project. The carbon-smoke screen, therefore, contributed to the measured reduction of thermal radiation at the instrument station. The thermal flux in the direction of air zero, measured with 180° field-of-view calorimeters, was 0.8 + 0.1 cal/sq cm. The flux measured with instruments of two other types was less than 0.7 cal/sq cm. The incident thermal flux, without smoke, at this distance was 57.5 + 5.0 cal/sq cm. The attenuation of radiant energy by the carbon and fog-oilsmoke was therefore 98.6 + 0.3%. Based upon measurements of radiant-energy attenuation made solely within the carbon smoke, it has been estimated that the carbon smoke reduced the incident radiation from 57.5 to 6.8 cal/sq em. The actual attenuation of thermal radiation by the fog-oil smoke screen was, therefore, ra from approximately 6.8 to 0.8 cal/sq cm, or 85% to 90%. -953. A preliminary report of this work appeared as CRLR-190 and UKP-58. CRLR ~ 299 - RADIOACTIVE PARTICLE STUDIES INSIDE AN AIRCRAFT (WT-717). Nicholas 8. Capasso, William M. Home, and John M. Roady, 4 December 1953. (Operation KNOTHOIE) on CONFIDENTIAL —a The object of Project 2.1 was to determine the physical nature and concentration of atomic-bomb-cloud particulate matter entering aircraft through the cabin-pressurization system.