sion neutrons has little effect on the shape of the distribution. Fine details in the behavior of V(A) may be obscured by the dispersion in mass. The result of v(A) for Pu 239 + wt n 9 is shown for comparison with the U 238 results. The fissioning nuclei are similar and the difference in the two curves is presumably mainly due to the difference in excitation energy. The difference in v(A) seems to be much larger for the heavy fragments than for the light fragments. Figure 3 shows V(A) plotted for groups of "reduced" total kinetic energies Eg defined by £% = EK(239/2) 2 /(239-A)A. V(A) is shown for groups of "reduced" total kinetic energy £% rather than the uncorrected kinetic energy Ej^ in order to eliminate to a first approximation the effect of the charge division (as correlated with the mass division) on the variation of the total kinetic energy. Britt, Wegner, and Gursky 10 have found that in medium-excitation fission the average Ej( (they use a parameter called "scission distance" which is inversely proportional to E^) is lower for events in the symmetric mass region than for events in the asymmetric region and have suggested that the symmetric fission events appearing in medium-excitation fission are due to a second "fission mode" not influenced by shell structure of the fragments and occurring with increasing yield as the excitation energy increases.The graph for high values of EK [ Fig. 3(a)] shows very strong variations in number of neu-We wish to present a model which gives a good description of the energy spectra of O 16 and neighboring nuclei. An outstanding property of O 16 is the coexistence of low-lying states with so widely divergent characteristics that they have hitherto been described by unrelated models, e.g., developments of the spherical shell model using the particle-hole picture for negative parities 1 and trons as a function of mass and very asymmetric mass distribution, whereas the sawtooth behavior becomes less pronounced as Ej£ decreases and the symmetric mass yield increases [Figs. 3(b) and 3(c)]. For very low Ej£ there is no minimum of V{A) at A = 130; this function increases smoothly in the symmetric mass region between A = 115 and A -140 as also observed by Schmitt and Konecny 3 in the symmetric mass region of Ra 226 .

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