74 CROCKER, KAWAHARA, AND FREILING Sedan was the well-known 100-kt cratering shot for the Plowshare program. The device was buried 635 ft below the surface in alluvial material in Area 10. NRDL collected samples at stations within 1 to 3.6 miles of ground zero. Analyses were performed on about 50 samples for the short list of nuclides previously given, and about one-third of these were analyzed for the longlist. TREATMENT OF THE DATA The radiochemical analytical work was contracted out to three commercial laboratories since NRDL does not have facilities for handling a large volume of samples for routine analysis. The contractors were also intended quired nearly the analyses. selected on to serve for a year for The results the basis of qualification tests, which were interlaboratory calibration purposes. It reall the contractors to complete and report were reported to NRDL as disintegrations per minute or equivalent ?U thermal-neutron fissions at shot time. NRDL then converted the values to equivalent fissions of the device at shot time, using mass-chain yield values supplied by the weapons laboratories. At the same time the calibration factors derived from the qualification-test analyses were applied. As a reference nuclide *Zr was chosen for fractionation studies. Some such choice seems unavoidable if fractionation is to be discussed. Zirconium-95 belongs to a class of nuclides (other members are °°Mo, ‘“4Ce, and ‘4"Nd) that are generally present in debris in equal quantities when expressed as equivalent fissions. Strontium-89, on the other hand, shows wide variation when compared with any of these. The ratio of equivalent fissions of ™Sr to equivalent fissions of Zr is, in fact, a fairly good indicator of the degree to which a sample is fractionated. The ratio will be 1 for an unfractionated sample, less than 1 for a sample depleted in Sr, and greater than 1 for a sample enriched in ®sr. The behavior of other fractionating nuclides can be correlated with that of "Sr by log—log plotting. The logof the ratio, r; 9., of equivalent fissions of nuclide i to equivalent fissions of *°Zr is plotted against the log of the similar ratio for “Sr and *Zr. The data so treated can be fitted more or less satisfactorily to a straight line. The slope of the line is then an indication of the extent of fractionation of nuclidei. RESULTS AND DISCUSSION For the Johnie Boy and Small Boyshots, the local-fallout collections were sufficient to define the geographical extent of the close-in