| quae fallout pattern, activity characteristics, particle size, and radiochemical content of each, Study was also made of the rate of fallout during the first 6-+ hr following each shot. Mike-shot samples of 0.54 sq in ranged from 109 to 1023 disintegrations/min, equivalent to as high as 2,750 c/sq ft. The fallout from Mike Shot continued for at least 6 hr within 15 mi of ground zero, but was heaviest during the first 30 min after detonation. shot decay slope was -2.1 for the period from Hy + The average Mike- 190 hr to Hy + 500 hr. More than 90% of all the Mike-shot fallout studies consisted of particles less than ly in diameter, but about 94% of the radioactive particles studied were larger than 10. Less than 1% of all the solid particles counted by light-microscope methods were radioactive, indicating that little respiratory hazard existed. ’ Activities of the King-shot samples were lower by a factor of 103 to 109. These activities ranged up to 9.2 x 107+ ¢/sq ft. The average King-shot decay slope was -0.65 for the period R + 150 hr to 150 hr to By + 450 hr. A preliminary report of this work appeared as CRLIR-ll2. CRLR - 218 - A SIMPLIFIED PROCEDURE FOR REFILLING GEIGER-MUELLER TUBES. Henry A. Garon, 11 June 1953. UNCLASSIFIED (U) A relatively simple method has been devised for refilling discarded Geiger-Mueller tubes and preparing them for re-use. New tubes have average lives of 107 counts and are relatively expensive as compared with the refilled tubes which have life expectancies of between 1 x 108 and 5 x 108 counts. The processes of mica-window replacement, tube evaucation and refilling, and tube sealing and testing are described in detail. The mixture found to be optimum for tube wfilling is a 24 to 1 ratio of helium gas to absolute ethyl alcohol vapor (total pressure within the tube: 25 em of Hg). Refilled tubes with replaced mica windows were found to operate satisfactorily at an altitude of 8,000 ft. Theoretically, such tubes shculd perform satisfactorily up to 30,000 ft.