Excitation curves at 0° and 90° were studied for neutrons and $\gamma$ rays produced in bombardment of thin targets of ${\mathrm{Be}}^9$, ${\mathrm{B}}^{10}$, ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{13}$, and ${\mathrm{O}}^{18}$ by $\alpha$ particles with energies of from 1.8 to 5.3 Mev. Resonances were observed in the ${\mathrm{Be}}^9(\alpha , n){\mathrm{C}}^{12}$ reaction at bombarding energies of 1.9, 2.3, 2.6, 3.98, 4.4, and 5.0 Mev. The ${\mathrm{C}}^{13}(\alpha , n){\mathrm{O}}^{16}$ reaction showed resonances at 2.09, 2.25, 2.42, 2.605, 2.69, 2.775, 2.825, 3.09, 3.33, 3.42, 3.67, 3.73, 4.125, 4.42, 4.50, 4.63, 4.75, and 5.05 Mev. The ${\mathrm{B}}^{10}(\alpha , n){\mathrm{N}}^{13}$ excitation curve has resonances at 2.16, 2.25, 2.90, 4.53, 4.85, and 5.36 Mev, while the $\gamma$-ray yield from the ${\mathrm{B}}^{10}(\alpha , p\gamma ){\mathrm{C}}^{13}$ reaction showed all these as well as resonances at 3.6 and 3.95 Mev. The ${\mathrm{B}}^{11}(\alpha , n){\mathrm{C}}^{13}$ reaction has resonances at bombarding energies of 2.06, 2.60, 2.93, 2.97, 3.23, 3.54, 3.72, 3.92, 4.25, 4.34, and 5.00 Mev. The ${\mathrm{O}}^{18}(\alpha , n){\mathrm{Ne}}^{21}$ reaction was studied with a thicker target (90-130 kev). Resonances in the neutron yield were resolved at 2.21, 2.47, 2.57, 2.72, 2.94, 3.24, 3.63, 3.91, 4.12, 4.22, 4.33, 4.52, and 4.82 Mev. Cross sections and widths of the resonances in the various reactions were determined.

• Received 20 February 1956

DOI:https://doi.org/10.1103/PhysRev.102.1348