Two-dimensional pulse-height analysis has been used to search for double gamma-ray emission in competition with the $E0\left(\pi \right)$ decay of the 6.05-MeV state in ${\mathrm{O}}^{16}$ and in competition with the $E2\mathrm{}$ gamma-ray decay of the 4.43-MeV state in ${\mathrm{C}}^{12}$. In each case two 5-in.×5-in. NaI crystals viewed the target located at the center of a double-conical lead-Hevimet absorber, and the outputs of these detectors were connected to a 64×64 two-dimensional pulse-height analyzer. Coincidence patterns were analyzed for the presence of a line of constant sum-energy with an intensity distribution peaked at the center in accordance with the theoretical $E^3{(E_0-E)}^3$ distribution. In neither case was any evidence obtained for such a pattern. Upper limits of $\frac{{\Gamma }_{E1E1\mathrm{}}}{{\Gamma }_{E0\left(\pi \right)}}\le 1.1\times {10}^{-4\mathrm{}}$ for the 6.05-MeV state of ${\mathrm{O}}^{16}$ and of $\frac{{\Gamma }_{E1E1\mathrm{}}}{{\Gamma }_{E2\mathrm{}}}\le 0.5\times {10}^{-4\mathrm{}}$ for the 4.43-MeV state ${\mathrm{C}}^{12}$ were derived.

• Received 13 March 1964

DOI:https://doi.org/10.1103/PhysRev.135.B294