54 MILLER AND SARTOR fractions of gross samples was measured either with the ion chamber or with a calibrated gamma Scintillation counter, The activity of many samples was measured with both instruments, The measured ion currents in milliamperes and the photon pulse rates in counts per minute for each sample were decay-corrected to 100 hr after detonation. If the measured ion current per *57r fission at 100 hr from the ion chamber is designated as i(100) and the calculated ion current per fission for the unfractionated fission product at 100 hr after fission is designated as i,(100), then the gross fractionation number for the measured sample at 100 hr is i(100) r,,(100)= i,(100) (13) The definition of the r,, by ratios of the ion currents from the ion chamber implies the assumption that i/i) is equal to I,/I°, where I! is the roentgens per hour for an unfractionated fission-product mixture. This assumption is fairly valid for most measurements on fissionproduct mixtures.’ For correlation purposes, a fractionation number, Tho? is defined for the calibrated gamma-scintillation-counter mea- surements as i’(100) r/,(100) = ig(100) (14) where i’(100) is the observed counting rate per »Zr fission at 100 hr after detonation for a sample of fallout and ij(100) is the calculated counting rate per fission for the unfractionated fission-product mixture. The r,, of Eq. 12 is for the i ratios at 1 hr after detonation rather than at 100 hr. For evaluation of r,;, the i(100) values were decaycorrected to 1 hr after detonation (or after fission). The assumed decay-correction factors for i and i’ are represented by i(1) = 250 i(100) (15) i’(1) = 200 i’(100) (16) and The only available computed values of i, and ig for the 47 ion chamber and the calibrated gammascintillation counter, respectively, are those>’’ for the products from thermal-neutron fission of “°U. For this mixture i,(100) is 2.48 x 107° ma/fission and ij(100) is 2.10 x 107° counts/min per fission. The two respective calculated decay-correction factors from 100 to 1 hr after fission are represented by