all steps of the procedure to eliminate possible errors due to incomplete extraction of uranium, e. change in volume of the ethyl acetate, and related problems Measurement of the Fluorescence. The instrument used is a Jaco Galvanek-Morrison Fluorometer, 16 construction details of which can be ob- tained from the Jarrel-Ash Company. a Filtered 3600 A light is focused on the uranium sample and the resulting visible fluorescent light is filtered thru Corning 3484 and 9780 filters to isolate the 5500 Auranium fluorescence. A 931A photomultiplier with peak re- sponse at 5500 Ais used to measure the light intensity. is essentially a vacuum tube voltmeter. the sensitivity range. The measuring circuit Shunt switches are provided to vary A warm-up time of at least 15 minutes, preferable an hour, is required for stable operation. The intensity of the emitted fluorescent light is known to be a linear function of the uranium present (from 0.001 to 10 pg of uranium) and the response of the instrument is also known to be linear at a constant level of illumination. The intensity of fluorescence of the blanks, the standards, and the filter paper samples are measured and the amount of uranium found in a given Sample is calculated in the following way. If Fo is the reading for a standard known to contain S.uwg of uranium; Fy is that of a filter paper sample and Fp that of the blank, then the pg of uranium in a sample is: Fy -F Hg Uin sample = 5 _* Fs -Fp The duplicate measurements should agree to at least 10%; if not, additional determinations must be made since accidental contamination or loss is indicated. . If one knows the fraction of the original filter paper solution actually transferred to a dish, the bombfraction (BF) present in the solution of the dissolved filter paper may now be calculated. The following formula includes all of the measured quantities. pr - 11, 42, Us. Vg Aw 1000 43° «(Fx -Fa) 1 Vz, (Fo-Fp) Ur op. Galvanek, Jr. andT. J. Morrison, Jr., US AEC, ACCO-47 (1954). 5496 ony C7 ca ? Jarrell-Ash Co., 26 Farwell St., Newtonville, Mass. - 48 - v A