Experimental Evidence forα-Particle Doorway States in theC12+C12Reaction

Quartet states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ are preferentially populated in the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},\alpha ){}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=5.7,6.0, \mathrm{and} 6.3$ MeV. This may be due to $\alpha$-particle doorway states having a large overlap with quartet states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$. The interpretation of the correlated resonances in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ system as intermediate structure resulting from $\alpha$-particle doorway states is supported by the results of the measurement reported.