The properties of certain energy levels in ${\mathrm{O}}^{16}$, ${\mathrm{F}}^{19}$, and ${\mathrm{Ne}}^{20}$ have been studied by observations on the alpha particles and inelastic protons from the bombardment of fluorine by protons. A highresolution magnetic analysis of the alpha-particle groups to the $2^{+}$ and $1^{-}$ levels in ${\mathrm{O}}^{16}$ from the ${\mathrm{F}}^{19}(p, \alpha ){\mathrm{O}}^{16*}$ reaction failed to reveal any doublet structure in these known levels. The angular distributions of the alpha-particle groups to these levels did not indicate degeneracy with a $2^{-}$ level, nor did a search for new excited levels in ${\mathrm{O}}^{16}$ up to 8.7-Mev excitation reveal a $2^{-}$ level. These results are not in agreement with the alpha-particle model of the ${\mathrm{O}}^{16}$ nucleus which predicts a $2^{-}$ state close in energy to the $2^{+}$ state.

Angular distributions of the alpha particles were measured at proton bombarding energies of 873, 935, 1290, 1355, and 1381 kev. The distributions at 1355 kev indicated that the corresponding ${\mathrm{Ne}}^{20}$ resonance level at 14.16 Mev has spin 2 and odd parity. The spin and parity assignments previously found for the other levels were confirmed.

A study of the inelastic proton groups from the ${\mathrm{F}}^{19}(p, p^{\prime }){\mathrm{F}}^{19*}$ reaction gave 108.8±0.8 and 196.0±1.4 kev for the excitation energies of the two lowest excited levels of ${\mathrm{F}}^{19}$. The cross sections at the 1431-kev resonance for these groups in the center-of-mass system were 0.187±0.015 barn for the first group and 0.007 ±0.002 barn for the second group. At 1381 kev the cross section was 0.0427±0.0040 barn for protons to the second excited level.

Angular distributions of the proton groups were measured and, in conjunction with other studies made in this laboratory, resulted in spin and parity assignments of ${\mathrm{½}}^{-}$ and ${\frac{3}{2}}^{+}$ for the first and second excited states of ${\mathrm{F}}^{19}$, respectively.

• Received 16 August 1954

DOI:https://doi.org/10.1103/PhysRev.96.1250