Scattering of 18.7-Mev Alpha Particles from Al, Cu, and Ag

The scattering of 18.7-Mev alpha particles from Ag, Cu, and Al was studied from 10° to 170° with rms angular resolutions of 0.4° to 0.85°. The scattered alpha particles were separated from singly charged reaction products with the aid of a proportional counter, and their energies were measured with a CsI(Tl) scintillation spectrometer. The elastic scattering for Ag shows the "exponential" dropoff from the Coulomb cross section, without any pronounced structure at large angles. For Cu, definite changes in the slope of the dropoff are observed up to 120°, followed by a shallow minimum near 130° and a very deep, narrow minimum at 162° (c.m.). The interaction radii deduced from the strong-absorption model agree with those found at higher energies. From the diffraction-like pattern found for Al, an interaction radius of 6.4×${10}^{-13\mathrm{}}$ cm is derived, appreciably larger than the one obtained at 40 Mev (5.4×${10}^{-13\mathrm{}}$ cm). There are indications that a direct-process interpretation of the inelastic scattering from Al is possible.