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 UNITED STATES ATOMIC ENERGY COMMISSION 
 
 RANGES IN AIR OF PLUTONIUM FISSION FRAGMENTS AS A 
 FUNCTION OF THEIR MASS 
 
 by 
 
 S. Katcoff 
 J. A. Miskel 
 
 Los Alamos Scientific Laboratory 
 
 This document consists of 3 pages. 
 Date of Manuscript: October 16, 1946 
 Date Declassified: March 6, 1947 
 
 This document is for official use. 
 
 Its issuance does not constitute authority 
 
 for declassification of classified copies 
 
 of the same or similar content and title 
 
 and by the same author(s). 
 
 i 
 
 Technical Information Division, Oak Ridge Directed Operations 
 Oak Ridge, Tennessee 
 
RANGES IN AIR OF PLUTONIUM FISSION FRAGMENTS AS A 
 FUNCTION OF THEIR MASS 
 
 By S. Katcoff and J. A. Miskel 
 
 It is possible to effect a partial separation of fission products by taking advantage of the varia- 
 tion in the range of fission fragments as a function of their mass. The same phenomenon can be 
 used to determine the mass numbers of previously unassigned fission products. In the experiments 
 reported here, the ranges in air of seven plutonium fission products have been determined and mass 
 numbers have been assigned to two of these. The straggling in the range has been determined for 
 each of these also. 
 
 The apparatus consists of a beryllium tube about 8 inches long and one inch in diameter, which 
 contains a thin flat plutonium foil at one end. Starting at about 4 inches from the plutonium, there 
 is a series of 14 zapon films (about 7 /ig/cm^ thick) spaced 1/8-inch apart. The tube is ordinarily 
 evacuated to an air pressure of 12.0 cm Hg and then irradiated in a high neutron flux at the center 
 of the Los Alamos water boiler. The zapon films are so situated that all fission fragments in the 
 mass range being studied, which do not strike the walls of the tube, are stopped in the region of 
 the zapon films. They then diffuse to the nearest film where they remain. Nearly all of the stopping 
 material is air. 
 
 After irradiation, each zapon film (except the first and last). Is radiochemically analyzed for a 
 few fission products. The activities found on each film are corrected to the same solid angle and 
 then plotted against distance of dry air traversed by the fragments, as in Figure 1. The distance 
 
 33h Ce"'l 
 
 0.2 0.4 0.6 0.8 1.0 1.2 -1.4 1.6 1.8 2-0 2.2 2.4 2.6 
 RANGE IN AIR (CM AT NTP) 
 
 Figure 1. Differential range curves. 
 
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 o72 074 06 ote To ^7^ Ti its ti a.of 2^| 2.4 Te 2.8 
 
 RANGE IN AIR (CM AT NTP) 
 
 Figure 2. Integral range curves. 
 
 is corrected to 76.0 cm Hg pressure, to 15°C, and account is taken of the thickness of zapon trav- 
 ersed. By integrating the area under these curves, integral range curves are obtained, as in 
 Figure 2. The straight portions of these are extrapolated to zero activity to give extrapolated 
 ranges. 
 
 So far, 8 fission products in the heavy group have been investigated. The extrapolated ranges 
 and widths at half height of the differential range curves are listed in the following table. The re- 
 sults for 85 m Ba"^ are considerably distorted because of diffusion of its 41 sec Xe ancestor 
 through, or around, the zapon films; therefore, they are omitted from the table. 
 
 93 h 
 
 Sb'" 
 
 4.2 h 
 
 77 h 
 Te''^ 
 
 60 m 
 
 43 m 12.8 d 33 h 
 
 rpgi34 Ba'*" Ce'" 
 
 Extrapolated 
 range 
 
 Straggling 
 
 2.317 
 cm 
 
 13.2% 
 
 2.296 
 
 11.7% 
 
 2.253 
 11.9% 
 
 2.232 
 
 10.8% 
 
 2.210 
 
 9.6% 
 
 2.108 
 
 2.084 
 
 10.4% 11.5% 
 
 The results for 60 m Te"^ and 43 m Te^** were obtained by analyzing for their 22 h I and 54 m I 
 daughters, respectively. 
 
 In Figure 3, the ranges are plotted against the mass numbers. A straight line has been drawn 
 through the points in the absence of a better approximation. Masses 132 and 134 were previously 
 unassigned, but it is now obvious from Figure 3 that they should be assigned to 77 h Te and 43 m Te, 
 respectively. The results reported here should be considered only as tentative because the experi- 
 ments are still in progress. 
 
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 2.08 2.10 2.12 2.14 2.16 2.n8 2.20 2.22 2.24 2.26 2.28 2.30 2.32 
 RANGE IN AIR (CM AT N T P) 
 
 Figure 3. Ranges of F>u fission fragments in air as a function of mass. 
 
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