The total gamma absorption cross section has been measured for ${\mathrm{Be}}^9$ from 20.04 to 21.24 MeV, ${\mathrm{O}}^{16}$ from 20.37 to 22.04 MeV, ${\mathrm{F}}^{19}$ from 19.97 to 20.46 MeV, and ${\mathrm{Al}}^{27}$ from 20.37 to 20.88 MeV using monochromatic gamma rays from the ${\mathrm{T}}^3(p, \gamma ){\mathrm{He}}^4$ reaction. The ${\mathrm{Be}}^9$ nuclear cross section showed structure at 20.47±0.04 MeV and 20.73±0.04 MeV with integrated cross sections of 0.45 and 0.90 MeV-mb, respectively. The ${\mathrm{O}}^{16}$ nuclear cross section contained a broad peak at 21.02±0.04 MeV with an integrated cross section of 10.4 MeV-mb. There is some indication that this peak is composed of two narrower peaks at about 20.86 and 21.05 MeV. There is also some indication of structure at 20.62 MeV. Above about 21.6 MeV, the ${\mathrm{O}}^{16}$ cross section is rising sharply, consistent with the giant resonance peak above 22 MeV. The ${\mathrm{F}}^{19}$ cross section has a peak at 20.09±0.05 MeV with an integrated cross section of 3.5 MeV-mb. The ${\mathrm{Al}}^{27}$ cross section showed no structure in the energy region investigated.

• Received 14 February 1964

DOI:https://doi.org/10.1103/PhysRev.135.B129