Angular-Correlation Studies for theC12(He3, αγ)C11,C12(He3, pγ)N14, andO18(p, αγ)N15Reactions

The particle-gamma angular correlation method of Litherland and Ferguson was used to gain information on the decay modes and spin assignments of the ${\mathrm{C}}^{11}$ 2.00-MeV level; the ${\mathrm{N}}^{14}$ 5.83- and 7.03-MeV levels; and the ${\mathrm{N}}^{15}$ 5.28-, 6.33-, 8.31-, and 8.57-MeV levels. The ${\mathrm{C}}^{12}({\mathrm{He}}^3, \alpha ){\mathrm{C}}^{11}$, ${\mathrm{C}}^{12}({\mathrm{He}}^3, p){\mathrm{N}}^{14}$, and ${\mathrm{O}}^{18}(p, \alpha ){\mathrm{N}}^{15}$ reactions were used to populate the levels. Protons and $\alpha$ particles were detected in an annular counter at 170° to the beam and gamma rays were detected at angles between 20 and 90° to the beam. The spin of the ${\mathrm{C}}^{11}$ 2.00-MeV level was found to be ½, $\frac{3}{2}$, or $\frac{5}{2}$ with the quadrupole-dipole mixing parameter of the 2.00 → 0 transition given by $x=+(0.27\mathrm{}\pm 0.07)$, or $\mathrm{}\left|x\right|>11\mathrm{}$ for $\frac{3}{2}$ and $x=-(0.18\mathrm{}\pm 0.07)$ for $\frac{5}{2}$. The angular distribution of the ${\mathrm{N}}^{14}$ 7.03 → 0 transition gave $0.15<~x<~1.15$ for this $J=2\mathrm{}$ to $J=1\mathrm{}$ transition. A 7.03 → 3.95 transition was observed with a branching ratio of 9±5%. The results for the ${\mathrm{N}}^{14}$ 5.83-MeV level were consistent with earlier work. The ${\mathrm{N}}^{15}$ 5.28-MeV level was assigned $J^{\pi }={\frac{5}{2}}^{\mathrm{}(+)\mathrm{}}$ with a value of - (0.15±0.06) or + (6.1±1.4) for the octupole-quadrupole mixing ratio of the 5.28 → 0 transition. The ${\mathrm{N}}^{15}$ 6.33-MeV level was assigned $J^{\pi }={\frac{3}{2}}^{\mathrm{}(-)\mathrm{}}$ with a value of + (${0.09}_{-0.03\mathrm{}}^{+0.06\mathrm{}}$) or + (${1.4}_{-0.4\mathrm{}}^{+0.1\mathrm{}}$) for the 6.33 → 0 mixing ratio. Most probable assignments of ${\mathrm{½}}^{+}$ and ${\frac{3}{2}}^{+}$ are made to the ${\mathrm{N}}^{15}$ 8.31- and 8.57-MeV levels on the basis of this and previous work. The results are compared to shell-model predictions.