Evidence is presented for the occurrence of superdeformation in $\mathrm{sd}$-shell nuclei. Neutron-proton coincidence spectra from the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ reaction at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=24\mathrm{}$ MeV were measured. The neutron evaporation spectrum at low energies directly reflects the large deformation of the emitting system, extending to states above the yrast line. The strong energy dependence of the effect implies that the compound nucleus undergoes a rapid change from nearly spherical to superdeformed shapes over a narrow range of excitation energy. The transition to a fissioning system should be observable.

• Received 19 February 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1178