Study of Levels inO18through the Radiative Capture of Alpha Particles byC14

Abstract

Two resonances in the reaction ${\mathrm{C}}^{14}(\alpha , \gamma ){\mathrm{O}}^{18}$ have been studied at laboratory alpha-particle energies of 1.142±0.010 and 1.790±0.010 Mev. These correspond to excited states in ${\mathrm{O}}^{18}$ at 7.127 and 7.630 Mev. At the upper resonance only two primary transitions are observed leading to the ground state of ${\mathrm{O}}^{18}$ and the first excited state at 1.98 Mev. Their angular distributions along with other evidence unambiguously establish spins and parities of 1 - for the 7.63-Mev state, 2+ for the 1.98-Mev state, and 0+ for the ground state. Values of $\gamma =\frac{{\Gamma }_{\alpha }\Gamma \gamma }{\Gamma }$ of 80 and 160 millielectron volts, respectively, are obtained for the 7.63- and 5.65-Mev $E1\mathrm{}$ primary transitions. At the lower resonance again only two primary transitions are observed leading to levels in ${\mathrm{O}}^{18}$ at 1.98 and 3.55 Mev. Greater than 96% of the decays of the 3.55-Mev level lead to the 1.98-Mev level. Analysis of the angular distributions of the four gamma rays observed in the direct spectrum at this resonance, with respect to the incident beam, unambiguously establish spin and parity of 4+ to both the capturing state at 7.13 Mev and the level at 3.55 Mev. Values of $\gamma$ of 15 and 12 milli-electron volts, respectively, are obtained for the 3.58-Mev $M1\mathrm{}$ and the 5.15-Mev $E2\mathrm{}$ primary transitions. The amount of $E2\mathrm{}$ mixing in the former transition is very small.