Absolute cross sections for the elastic scattering of alpha particles by ${\mathrm{O}}^{16}$ have been measured in a differentially pumped gas scattering chamber. The measurements were made for laboratory energies from 3.7 to 6.5 Mev, corresponding to 7.7- to 9.9-Mev excitation in ${\mathrm{Ne}}^{20}$, at center-of-mass angles of 168.9°, 149.4°, 140.8°, 125.3°, and 90.0°.

Narrow resonances were observed at bombarding energies of 5.002, 5.11, 5.190, 5.432, 5.532, and 6.030 Mev. The data were analyzed in terms of Wigner-Eisenbud dispersion theory to find the spins, parities, resonant energies, widths, reduced widths, and characteristic energies of the levels. The resonances observed correspond to states in ${\mathrm{Ne}}^{20}$ with the following excitation energies, spins, and parities: 8.755($1^{-}$), 8.84($5^{-}$), 8.905($1^{-}$), 9.099($4^{+}$), 9.179($3^{-}$), and 9.577 Mev ($2^{+}$). In order to obtain a good fit to the data, it was necessary to assume the existence of two broad overlapping resonances, one at ∼8.7-Mev excitation ($0^{+}$) and the other at ∼8.8 Mev ($2^{+}$). There is also some evidence for the presence of a broad $4^{+}$ level at an energy higher than 9.9-Mev excitation in ${\mathrm{Ne}}^{20}$.

• Received 19 October 1959

DOI:https://doi.org/10.1103/PhysRev.118.175