A correlation between the absence of nonstatistical sub-Coulomb resonant structure in many reactions previously studied and the density of levels in the associated compound (or precompound) nucleus is noted and discussed in terms of the intermediate structure model of nuclear reactions. Such a correlation would predict the absence of structure in the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ system, in disagreement with a previous measurement of excitation functions for the production of $\gamma$ radiation. Excitation functions for the reactions ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({}_{}{}^{14}{}_{}{}^{}\mathrm{N},p){}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({}_{}{}^{14}{}_{}{}^{}\mathrm{N},d){}_{}{}^{26}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({}_{}{}^{14}{}_{}{}^{}\mathrm{N},\alpha ){}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},\alpha ){}_{}{}^{17}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},p){}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ have been measured in the region of the Coulomb barrier in a search for resonance structure of the "quasimolecular" type observed in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ scattering. The present measurements of excitation functions for charged-particle production in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ + ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ do not exhibit any correlated resonances. The ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ system at the Coulomb-barrier energy produces ${}_{}{}^{21}{}_{}{}^{}\mathrm{Ne}$ in a region of excitation where the level density is relatively low and hence could be a reaction in which intermediate structure might be observed. The excitation functions measured for $\alpha$-particle production show fluctuations, but with no apparent correlations.

[NUCLEAR REACTIONS ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({}_{}{}^{14}{}_{}{}^{}\mathrm{N},\alpha )$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({}_{}{}^{14}{}_{}{}^{}\mathrm{N},p)$, ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({}_{}{}^{14}{}_{}{}^{}\mathrm{N},d)$, $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=7.0-10.0\mathrm{}$ MeV; measured ${\sigma }_{\alpha +p+d}\mathrm{}\left(E\right)\mathrm{}$, ${\sigma }_p\mathrm{}\left(E\right)\mathrm{}$, ${\sigma }_d\mathrm{}\left(E\right)\mathrm{}$; ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},\alpha )$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},p)$, $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=2.40-6.34\mathrm{}$ MeV; measured ${\sigma }_{\alpha +p}\mathrm{}\left(E\right)\mathrm{}$; searched for nonstatistical resonances in Coulomb barrier region; discussed systematics of "quasimolecular" resonances.]

• Received 11 February 1974

DOI:https://doi.org/10.1103/PhysRevC.9.1760