The yield of elastically scattered protons from oxygen was measured with a magnetic analyzer which detected protons scattered through laboratory angles of 159° to 169°. Using protons accelerated by an electrostatic generator, the proton energy range from 0.6 to 4.5 Mev was covered in 4.4-kev or smaller steps. Two sharp resonances were observed, one at an incident proton energy of 2.66 Mev with a width of 19.9 kev, and the second at 3.47 Mev with an observed width less than 3.5 kev. Near 4.0 Mev a broad maximum in the cross section was obtained, and a broad resonance appears to give another maximum slightly above 4.5 Mev. The resonance at 2.66 Mev appeared as a nearly symmetrical dip in the scattering cross section.

The capture cross section of oxygen for protons was measured for incident proton energies from 1.4 to 4.1 Mev by counting the positrons from the decay of ${\mathrm{F}}^{17}$ built up under the bombardment of oxide targets. Up to a narrow resonance at 3.47 Mev, the capture cross section was observed to increase almost linearly with energy. Above 3.75 Mev, the cross section was found to increase more rapidly to a maximum near 3.99 Mev.

On the basis of the scattering and capture data, energy levels have been assigned to ${\mathrm{F}}^{17}$ at 3.11, 3.88, 4.36, and 4.73 Mev, although the positions of the latter two levels are not clearly defined by the data.

• Received 18 June 1951

DOI:https://doi.org/10.1103/PhysRev.84.12