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Experimental nuclear charge dispersion curves from interactions of 11--29 Gev protons with /sup 238/U have been used in the construction of three-dimensional charge dispersion curves. They show the yield variation with mass number A. Neutron-deficient products are distributed over the entire mass range with a peak at A near 87, while the yield of neutron-excessive products is distributed only in the relatively narrow mass region between A=70 and A=150 and has a maximum around A=115. An isobaric yield curve has been obtained by summing up each of the charge dispersion curves and shows a peak, rather than the flat top, in the mass region A=80 to 140 reported previously. The mass yield curves of neutron-excessive and neutron-deficient products are obtained by a decomposition of the charge dispersion curve with two Gaussians, and the mechanism of formation is suggested.

Excitation functions and mean recoil ranges have been measured for radioactive products resulting from the helium-ion bombardment of natural zirconium and targets which were isotopically enriched in ${\mathrm{Zr}}^{90}$. Helium-ion energies varied between 25 and 80 MeV. Products observed were ${\mathrm{Mo}}^{90}$, ${\mathrm{Nb}}^{90}$, ${\mathrm{Zr}}^{89}$, ${\mathrm{Zr}}^{88}$, ${\mathrm{Y}}^{88}$, ${\mathrm{Zr}}^{87}$, ${\mathrm{Y}}^{87}$, ${\mathrm{Zr}}^{86}$, and ${\mathrm{Y}}^{86}$. The excitation function was also measured for the production of ${\mathrm{Y}}^{87}$. The recoil ranges are compared with the range theory of Lindhard, Scharff, and Schiott to determine the energy ranges over which the production of the nuclide is consistent with major contributions from a compound-nucleus mechanism. Excitation functions for products with $A\ensuremath{\ge}87$ were compared with the statistical model to investigate the influence of shell structure on level densities. The level-density models used were those due to Newton and to Rosenzweig in addition to the standard Fermi-gas level density. Rosenzweig's model gave the best over-all agreement with the experimental results, with the standard Fermi-gas level density a close second. Several excitation functions were calculated using the $s$-wave approximation to estimate the effect of $\ensuremath{\gamma}$-ray de-excitation due to angular-momentum restrictions. Threshold position and excitation-function widths were found to agree quite satisfactorily with experimental values when this was done.