Total cross sections of Be, ${\mathrm{B}}^{10}$, B, C, and O have been measured for neutrons of energies between 3.4 and 16 Mev. Neutrons of energy spreads between 15 and 40 kev were produced by bombarding tritium targets with protons or deuterium targets with deuterons, the charged particles being accelerated in a tandem electrostatic accelerator. Sharp peaks in the total cross sections of ${\mathrm{B}}^{11}$, C, and O yielded information about energy levels in ${\mathrm{B}}^{12}$, ${\mathrm{C}}^{13}$, and ${\mathrm{O}}^{17}$. None of the total cross sections of the five nuclei investigated showed sharp peaks above energies corresponding to an excitation energy of the order of 12 Mev of the respective compound nucleus. The transition from sharp structure to a slowly varying cross section occurs quite abruptly, except for the compound nucleus ${\mathrm{B}}^{11}$ which is excited to almost 12 Mev even for slow neutrons.

• Received 20 February 1961

DOI:https://doi.org/10.1103/PhysRev.123.209