CORRELATIONS ON DEBRIS FROM SILICATE BURSTS 79 the range was considerably wider. The slope values obtained from the Johnie Boy and the Small Boy data are in quite good agreement with each other. The Sedan data are also given for purposes of comparison along ~with slopes from previous correlations on a high-yield coralsurface burst and on some air bursts. A few interesting points with regard to &. of °Np in the 2 . may be mentioned. The nonfractionating behavior ralexsurface burst is at variance with its behavior in the ais* bursts,and the silicate bursts. On the other hand, **Mo fractionates in the. M@ar-burstg@ebut not in the other shots. There is an in- dication of possible sfight fractionationsof ‘4Ge in.Sedan andin the air bursts. In the silicate bursts ‘Cg fr&etionateg less than '"Cs. The fractionation -of‘the. latter is explainable ai?the‘basis of its rare-gas precursor, !*'Xe.”Cegium-136, on the_othen hand, is shiegied; i.c., it has no preétirsors. A possfite explanatjon#f its fractiongt n behavior lies in thé basicity of the alkali-meta¥oxide or hydroxide relative to the silicate sqil m. “* A reservation ‘should be noted for the slope values repiftted for the 103-, 106-, and 132-mass chains for Johnie Boy and Small Boy. There is some indication in each of these cases that the datd points belong to two different families and should not be fitted to the same straight line. The available data are unfortunately inadequate to resolve the question. Aside from the **Mo and ?Np anomalies just mentioned, insofar as the table permits one to judge, the differences in fractionation in the various kinds of bursts are of degree rather than Kind. Analysis on many samples separated into sieve fractions displays the trend of fractionation with particle size in a rough way. Figure 5 shows an example of these data from the Small Boy shot and also illustrates the variability of the ratios observed. The ratio of *Sr to *5Zr has been plotted against the sieve-opening diameter. There is, of course, no really accurate way of plotting these data. For example, any point on the right side of the 1580-y line corresponds to a sample that passed a No. 7 sieve (2800- openings) and was caught on a No. 12 sieve (1580-, opening’); padtinitiiy the.saihple mayciein”particles up to 2800 yu. The scatteMigat the points is @iught tape-dge to the combined effects of heterdgeneit prand wegseial)sarge. size.Atlleast two kinds of active particles, Sonia: a3rregélar particles, were discernible in these s ; cemales: ¢ ‘Heve4fractions consisted of only a few parftit ceo ‘pOMMeenS niay nothaveeen truly representative of their“particle--size classes. If an. dverage weighted according to sampte masses is taken, one obtaing,the, ints of Fig. 5 through which a line has been drawn. The figureis quite representative of the behavior of fractionating nuclides in both Small Boy and Sedan. The siéve data OR: theJohnie“Boy&pnples were too few to draw any conclusions relative to particle size.