The yield curve for the ${\mathrm{O}}^{16}(\gamma , n){\mathrm{O}}^{15}$ reaction has been examined in detail over most of the energy region between 15.6 Mev and 23.2 Mev. Fine structure in the form of sudden changes of slope, or "breaks" had been previously reported by the Saskatchewan group. The existence of these breaks was confirmed, and a number of new breaks have been found. The yield curve was analyzed for cross section in the vicinity of a break at 16.03 Mev, and it was found that the cross section has a resonance shape with a width of 18±5 kev. The yield curve breaks are interpreted as manifestations of narrow resonances in the cross section. Integrated cross sections, peak heights, and radiative widths were estimated for all the levels found. On the basis of the radiative widths, it is concluded that, below about 19 Mev the reaction proceeds by absorption of $E2\mathrm{}$ radiation, while between 22 and 23 Mev it proceeds principally by absorption of $E1\mathrm{}$ radiation. No conclusion could be drawn for the 20 to 21 Mev region. From a consideration of the total integrated cross section, and the cross section at 17.63 Mev it is concluded that the bulk of the gamma-ray absorption by ${\mathrm{O}}^{16}$ takes place into narrow levels.

• Received 1 August 1955

DOI:https://doi.org/10.1103/PhysRev.100.1377