The scattering of 18-Mev alpha particles by gaseous ${\mathrm{C}}_3$${\mathrm{H}}_8$, ${\mathrm{O}}_2$, and ${\mathrm{H}}_2$S targets was studied with a multiplate scattering chamber. The elastic angular distributions exhibit the diffraction-likfe pattern typical of light elements. Carbon and oxygen show a sharp rise above the Rutherford cross sections at the backward angles, with values $\frac{\sigma }{{\sigma }_R}$ of 660 for carbon and 350 for oxygen near 173°. A good fit to the angular distribution for inelastic scattering leading to the first excited state of ${\mathrm{C}}^{12}$ (4.43 Mev, $2^{+}$) is obtained using a ${\left[j_2\mathrm{}\right(\mathrm{qR}\left)\right]}^2$ dependence with $R=5.5\mathrm{}\times {10}^{-13\mathrm{}}$ cm. No direct-interaction analysis is possible for the alphaparticle groups corresponding to the 7.65-Mev and 9.61-Mev levels in ${\mathrm{C}}^{12}$ and to the excited states of ${\mathrm{O}}^{16}$ up to the 8.87-Mev level. All these distributions show strong forward peaking. In the case of inelastic scattering by ${\mathrm{S}}^{32}$ ($Q=-2.44\mathrm{}$ Mev), an interaction radius of 6.5×${10}^{-13\mathrm{}}$ cm can be deduced from the angular distribution, though the agreement with ${\left[j_2\mathrm{}\right(\mathrm{qR}\left)\right]}^2$ is rather poor. A summary of elastic scattering results for elements in the range from $Z=6\mathrm{}$ to $Z=47\mathrm{}$ is presented. Expressions for the second-order geometry and the multiple-scattering corrections are given.

• Received 15 July 1959

DOI:https://doi.org/10.1103/PhysRev.116.1184