The work here reported resulted in tables showing the accuracy of determinations to be a function of the number of counts taken and of the difference between counting rate and background. On the basis of 239 trials, consistent experimental results obtained with the Geiger tube and Berkely scaler proved closer to the average value than the theoretical dispersion would predict. Theory also requires that 215.1 values out of 239 be within the reliable error limits, whereas 213 experimental results actually fell within such limits. Elaboration on the findings of this investigation resulted in the following definition: "A detectable amount of radiation is that amount which shows an activity which has a statistical 9 chances out of 10 of being at least an infinitesimal amount above background.” TCIR - 535 - DECONTAMINATION OF AIRCRAFT CONTAMINATED IN FLIGHT BY AN AIR BURST OF AN ATOMIC WEAPON. (Operation SANDSTONE). Harry Levin and Homer F. Priest, 23 February 1950. CONFIDENTIAL-RESTRICTED DATA > A B-17 aircraft was flown through the cloud resulting from an air atomic burst, and was brought to Army Chemical Center one year later for decontamination. Exterior surfaces of the plane had been degreased in the interim, but no attempt had beer made to decontaminate the parts subjected to the tests reported here. The power plants were found to be the most highly contaminated sections of the plane, with recorded activity up to 26 mr/hr. Satisfactory decontamination of the engines was achieved only by complete disassembly and degreasing, chemical and mechanical decontamination of nonbearing — surfaces, and replacement of parts that presented special problems (e.g., braided ignition cables, etc.). Most of the contamination on supercharger air-compressor castings adhered strongly and persisted after degreasing ard other solvation processes. Mechanical action, ranging in degree from mild brushing to steel wool scouring was of definite value in removing contaminant. While mild decontaminants were moderately effective, best results were ob- tained from the use of harsher agents. Of the latter, phophoric-chromic acid and nitric-chromic acid gave best results, neither showing appreciable corrosive effect on the metal. Citric acid, previously recommended, had low decontamination efficiency.